Central versus peripheral thickness in the human cornea explained

PURPOSE

The human cornea is thicker in the periphery than the center and it has been suggested that this must be due to greater numbers of lamellae in the peripheral corneal stroma. The purpose of this study was to use high-resolution ultrastructural imaging to determine if the greater thickness of the peripheral cornea is due to the presence of more lamellae or if there is some other anatomical explanation.

METHODS

In this study, full thickness corneas from three human donors were processed for light microscopy (LM) and transmission electron microscopy (TEM). Images were taken in three distinct stromal regions (anterior, middle, and posterior) from the central and peripheral cornea. Stromal thickness was evaluated by LM while TEM was used to evaluate numbers and thicknesses of lamellae, mean collagen fibril diameter, and mean collagen fibril density.

RESULTS

Mean stromal thickness was significantly thinner in the central (415 ± 34 µm) compared to the peripheral (536 ± 29 µm) cornea (P = 0.009). Numbers of lamellae were not significantly different between central (246 ± 14) and peripheral (251 ± 14) cornea. Average lamellar thickness was not different across all regions of the cornea, except for the peripheral posterior where the lamellae were approximately 50 % thicker (P < 0.05). Collagen fibril diameters were larger in the peripheral cornea by approximately 30 % when compared to the central cornea, in all regions (P < 0.01).

CONCLUSIONS

This study shows that it is an increase peripheral posterior lamellar thickness, rather than an increase in the number of lamellae, that accounts for the increase in corneal stromal thickness in the periphery of the human cornea. While collagen fibril diameters are greater throughout the peripheral stroma, the lamellae in the mid and anterior peripheral stroma are not thicker than centrally.

Scleral lens induced short term corneal changes in eyes with Pellucid Marginal Degeneration

PURPOSE

To investigate the short-term effect of scleral lens (SL) on corneal curvature and corneal oedema in Pellucid Marginal Degeneration (PMD) eyes.

METHODS

Corneal anterior, posterior curvature and corneal thickness were measured in 14 eyes of 14 PMD participants with Schiempflug imaging at different corneal diameters and meridians at baseline and after 6 h of SL wear.

RESULTS

There was a significant flattening (up to 0.26 mm) of the anterior corneal curvature noted in the inferotemporal quadrant (from 210 to 255 degree at 2 mm, 8 mm and 10 mm corneal diameter), inferonasal quadrant (from 285 to 345 degree at 6 mm and 8 mm corneal diameter), and inferiorly at 2 mm and 10 mm corneal diameter (p < 0.05). Similarly, posterior corneal curvature showed statistically significant steepening mostly in inferotemporal quadrants (from 195 to 255 degree from 4 mm to 8 mm corneal diameter) and inferonasally at 2 mm and 4 mm corneal diameter (p < 0.05). A statistically significant increase in the corneal thickness noted in different corneal diameters with corneal oedema ranging from 2.10 % to 4.00 % after 6 h of SL wear. A gradual increase in corneal oedema was noted form centre to periphery. The baseline central fluid reservoir thickness (FRT) was 341.07 ± 139.8 which reduced to 276.71 ± 114.32 µm after 6 h of lens wear. No significant correlation was noted between corneal oedema with different parameters like initial and final FRT, change in anterior and posterior corneal curvature, and lens thickness (p > 0.05).

CONCLUSIONS

Short-term SL wear induced a clinically acceptable range of corneal oedema. A clinically significant flattening in anterior curvature and minimal steepening in posterior curvature were noted. Practitioners should be careful while measuring corneal parameters in PMD eyes wearing SL, as these alterations can provide false impression of disease progression.

Repeatability assessment of anterior segment measurements in myopic patients using an anterior segment OCT with placido corneal topography and agreement with a swept-source OCT

BACKGROUND

The precision of anterior segment biometric measurements in eyes has become increasingly important in refractive surgery. The purpose of this study is to assess the repeatability of the automatic measurements provided by a new spectral-domain optical coherence tomograph (SD-OCT)/Placido topographer (MS-39, CSO) and its agreement with a swept-source OCT (SS-OCT) biometer (CASIA SS-1000, Tomey) in patients with myopia.

METHODS

The right eye of 235 subjects was scanned 3 times with both devices. The evaluated parameters included central corneal radius of the steep meridian, central corneal radius of the flat meridian, mean central corneal radius, thinnest corneal thickness, central corneal thickness, anterior chamber depth, corneal volume and diameter. The intraobserver repeatability of the MS-39 measurements was calculated using intraclass correlation coefficient (ICC), within subject standard deviation, coefficient of repeatability, coefficient of variation and repeated-measures analysis of variance of the 3 repeated measurements. The agreement between the two devices was evaluated by 95% limits of agreement (LoA).

RESULTS

The majority of the parameters acquired from MS-39 showed high repeatability. The repeatability of corneal diameter was slightly lower than the other measurements, although the ICC remained high. Agreement with the CASIA SS-1000 was good, indicated by the Bland-Altman plots with narrow 95% LoA values for all parameters assessed.

CONCLUSIONS

The high repeatability of automatic measurements by the new device supports its clinical application in eyes with myopia, and the good agreement between the two devices indicates they could be used interchangeably for the parameters evaluated.

Distribution and determinants of corneal volume among healthy young Chinese adults: a cross-sectional study

BACKGROUND

Several studies have previously reported the normal values of corneal volume (CV) in various populations, whereas little is known about the CV distribution in healthy young Chinese adults. Our study aimed to investigate the distribution of CV and its relationships with other ocular biometric parameters among healthy young Chinese adults.

METHODS

A total of 1645 eyes from 1645 students at Dali University in Yunnan Province, China, were analyzed. Pentacam was used to measure CV. Central corneal thickness (CCT) and biomechanically corrected intraocular pressure (bIOP) were evaluated by Corvis-ST. Other biometrical parameters, including axial length (AL), keratometry, and white-to-white (WTW) distance, were measured using IOL Master.

RESULTS

The mean age of the study population was 19.01 ± 0.92 years, and 68.81% of them were women. The CV was normally distributed in the whole sample, with a mean value of 61.23 ± 3.22 mm3. CV and CCT were significantly smaller in the Yi ethnic group than in the Han ethnic group (p < 0.01). CCT (coefficient: 0.085; p < 0.001) and keratometry (coefficient: 0.422; p < 0.001) were positively correlated with CV, while AL (coefficient: -0.204; p < 0.001), WTW distance (coefficient: -0.236; p < 0.001) and bIOP (coefficient: -0.06; p < 0.001) were inversely associated with CV.

CONCLUSIONS

Our study provides an age-specific distribution of CV among healthy young Chinese adults. CCT, keratometry, AL, WTW distance and bIOP were important factors associated with CV.

Corneal layer thickness in keratoconus using optical coherence tomography

CLINICAL RELEVANCE

Accurate thickness measurement of corneal layers using anterior segment OCT can be used to improve visual outcomes. Understanding its applications is essential for optometric practices to enhance eye care procedures.

BACKGROUND

To evaluate the thicknesses of different corneal layers for identifying keratoconus (KCN) and subclinical keratoconus (SKCN) using spectral-domain optical coherence tomography (SD-OCT).

METHODS

This prospective study analyzed 60 eyes with KCN, 48 eyes with SKCN, and 53 normal eyes. The central corneal thickness (CCT) and thicknesses of the epithelium, Bowman, stroma, and Descemet-endothelium layers were measured using SD-OCT. One way analysis of variance and the area under the curve (AUC) were used to evaluate the parameters. The Delong method was used to compare AUCs.

RESULTS

In KCN, CCT and thicknesses of epithelium, Bowman, stroma, and Descemet-endothelium layers were 495.5 ± 41.7, 52.6 ± 6.4,11.5 ± 1.4, 415.5 ± 38.9, and 12.3 ± 1.7 µm, respectively. These thickness values were respectively 524.5 ± 33.3, 56.8 ± 6.8, 11.5 ± 1.6, 439.8 ± 30.6, and 12.4 ± 1.7 µm in SKCN and 563.8 ± 37.9, 57.7 ± 6.9, 12.2 ± 1.6, 469.5 ± 33.7, and 12.8 ± 2.1µm in normal group. Total cornea and stroma in KCN and SKCN, and epithelium in KCN were significantly thinner compared to the normal group (P < 0.001). The highest AUC values were observed for CCT in KCN (AUC 0.90) and SKCN (AUC 0.782). The diagnostic accuracy was significantly higher for stromal thickness in KCN (sensitivity 81.7%, specificity 73.6%, AUC 0.871) and SKCN (sensitivity 80.0%, specificity 56.6%, AUC 0.751) than other individual corneal layers (Delong, P < 0.001)                                    .

CONCLUSION

CCT can accurately distinguish keratoconus from normal eyes. However, central corneal stromal thinning was the most sensitive diagnostic index for early detection of SKCN. Developing standardized stromal maps may be helpful for detecting SKCN.

Comparison of central corneal thickness treated with small incision lenticule extraction, femtosecond laser-assisted in situ keratomileusis, or laser-assisted subepithelial keratomileusis for myopia

To compare the central corneal thickness (CCT) treated with small incision lenticule extraction (SMILE), femtosecond laser-assisted in situ keratomileusis (FS-LASIK), or laser-assisted subepithelial keratomileusis (LASEK) for myopia correction. This was a retrospective case series study. Patients who had completed 1-year follow-up after receiving SMILE, FS-LASIK, or LASEK at our hospital from January 2019 to July 2021 were included. Pentacam pachymetry was performed to measure the CCT. The predicted CCT reduction was obtained through laser platform. The measured CCT reduction was defined as the difference between the preoperative and postoperative CCT using Pentacam pachymetry. There were 100 eyes treated by SMILE, 100 eyes by FS-LASIK, and 100 eyes by LASEK. There was a significant difference in predicted CCT reduction among the three surgeries (P < 0.001), but no significant difference in measured CCT reduction postoperatively (PGroup = 0.373). At 1 year postoperatively, the CCT reduction was overestimated by 17.85 ± 5.36 µm in the SMILE group, underestimated by 4.31 ± 7.08 µm in the FS-LASIK group, and underestimated by 7.60 ± 8.28 µm in the LASEK group (PGroup < 0.001, PTime < 0.001). In the FS-LASIK group, the difference between predicted and measured CCT reduction was not related to the predicted CCT reduction (P = 0.095). The laser platform may overestimate the CCT reduction for SMILE and underestimate it for FS-LASIK and LASEK. FS-LASIK has a much higher level of accuracy in CCT reduction, which is not influenced by refractive correction.

Development of a novel protocol to evaluate contact-lens related ocular surface health on marmosets (Callithrix jacchus)

Contact lens wear affects the ocular surface and can cause contact lens-induced dry eye (CLIDE). The purpose of this study was bifold: (1) to develop a novel protocol to assess the ocular surface in a non-human primate (NHP) model, the common marmoset (Callithrix jacchus), and (2) to characterize central corneal thickness (CCT), tear osmolarity, blink rate and tear meniscus height (TMH) longitudinally, in untreated marmosets (controls) compared to animals treated with contact lenses (CL). Longitudinal changes in CCT (N = 10 control; N = 10 treated with contact lenses, CL-treated), osmolarity (N = 4 control; N = 6 CL-treated), blink rate (N = 8 control; N = 10 CL-treated) and TMH (N = 8 control; N = 6 CL-treated) were assessed using high frequency A-scan ultrasound, the I-PEN Vet Tear Osmolarity System, a video recording system (745 frames/minute) and Image J respectively, from 70 days to 224 days (5 months) at approx. 9am, and again after 9hrs of CL wear (methafilcon A, 55% water content; Capricornia, Australia) after every 4 weeks of contact lens wear for a total of 22 weeks of treatment. Repeated measures ANOVA was used to compare eyes over time and student t-test was used to compare treated to control eyes at each time point. At baseline, untreated marmosets had a CCT (mean ± SD) of 0.31 ± 0.01 mm, tear osmolarity (mean ± SD) 311.67 ± 11.48 mOsms/L, blink rate (mean ± SD) 1.83 ± 1.79 blinks per minute (bpm) and TMH (mean ± SD) 0.07 ± 0.02 arbitrary units (au), all of which remained stable over 5 months, except blink rate that increased to 5.32 ± 1.58 bpm (p < 0.01) after 5 months. In CL-treated marmosets, however, CCT progressively increased with CL wear (baseline: 0.30 ± 0.01 mm; 5 months: 0.31 ± 0.02 mm, p < 0.05), while osmolarity decreased after 2 and 3 months of CL wear (baseline: 316.11 ± 13.63; 2 months: 302.63 ± 11.27, p < 0.05; 3 months: 302.92 ± 14.58, p < 0.05). The decrease in osmolarity occurred in parallel to an increase in blink rate (baseline: 0.98 ± 1.18 bpm; 2 months: 3.46 ± 3.04 bpm, p < 0.05; 3 months: 3.73 ± 1.50 bpm, p < 0.001). TMH decreased during the third month of CL wear (baseline: 0.06 ± 0.00 au; 3 months: 0.05 ± 0.01 au, p < 0.05), and increased after 4 months (0.08 ± 0.01 au, p < 0.05). As TMH decreased, tear osmolarity increased in both control (R = -0.66, p < 0.05) and CL-treated marmosets (R = -0.64, p < 0.05). The results suggest that marmosets treated with CL for 5 months experienced an increase in blink rate, CCT and TMH, along with a decrease in osmolarity within the first few months of CL treatment that differed from the unaffected stable ocular surface findings observed untreated animals. We hypothesize that CL wear in marmosets might induce mild corneal edema, an increased blink rate and TMH, in turn delaying the development of hyperosmolarity. These findings confirm that the marmoset is a good novel animal model for ocular surface research for the assessment of novel contact lens materials aimed to alleviate CLIDE.

A lower birth weight percentile is associated with central corneal thickness thinning: Results from the Gutenberg Prematurity Eye Study (GPES)

PURPOSE

Prematurity, prenatal growth restriction, and retinopathy of prematurity (ROP) are associated with altered ocular geometry, such as a steeper corneal shape in childhood, but it is unclear whether perinatal history affects corneal thickness development, so this study investigated whether corneal thickness in adulthood is affected by perinatal history.

MARTERIALS AND METHODS

The Gutenberg Prematurity Eye Study (GPES) is a retrospective cohort study with a prospective ophthalmologic examination in Germany. The corneal thickness was measured by Scheimpflug imaging (Pentacam HR, Oculus Optikgeräte GmbH, Wetzlar, Germany), and the relationship between perinatal parameters respective birth weight percentile and corneal thickness at different locations was assessed using uni- and multivariable linear regression models. Covariates included age, sex, mean corneal radius, white-to-white distance, gestational age, birth weight percentile, ROP occurrence, and treatment. The main outcome measures were corneal thickness at the apex, the pupil center, and the corneal periphery.

RESULTS

The corneal thickness was measured in 390 participants (754 eyes, mean age 29.7+/-8.7 years, 224 females). In multivariable analyses, a lower birth weight percentile was associated with a lower corneal thickness at the apex (B = 0.20, p = 0.003) and the pupil (B = 0.19, p = 0.007). These effects diminished towards the corneal periphery and were not observed beyond the 4-mm diameter circle around the thinnest corneal position. Neither gestational age, ROP occurrence, or ROP treatment affected the corneal thickness.

CONCLUSION

A lower birth weight percentile in subjects born preterm as a proxy for restricted fetal growth is associated with corneal thickness thinning in adults aged 18 to 52 years, indicating that corneal thickness development, particularly in the corneal center, may originate in the fetal stage.

Case-control study of corneal topography and specular microscopy parameters in JIA patients with and without ocular involvement

PURPOSE

To assess corneal topography and specular microscopy values in juvenile idiopathic arthritis-related uveitis (JIA-U).

METHODS

This case-control study included 30 eyes from JIA-U patients, 20 eyes from JIA patients, and 50 eyes from age- and gender-matched healthy subjects. Patients with a history of ocular diseases or intraocular surgery were excluded. Corneal topography maps (Pentacam HR) and specular microscopy images (CellChek SL) were obtained. The measurements of the groups were compared.

RESULTS

Keratometric astigmatism was higher in the JIA-U group than in the control group (p = 0.040). Patients with astigmatism greater than 1.50D were more common in the JIA-U group than in the control group (p = 0.026). The JIA-U group had higher anterior and posterior elevation values than the control group (p = 0.006, p = 0.025). The density of endothelial cells, coefficient of variation, and hexagonality did not change across groups (p = 0.465, p = 0.096, p = 0.869). The total number of exacerbations and the duration of anterior chamber inflammation were both positively correlated with posterior elevation (r = 0.600, p 0.001; r = 0.583, p 0.001). The age of diagnosis was found to be negatively correlated with anterior elevation (r = -0.412, p = 0.021).

CONCLUSION

Corneal astigmatism, as well as anterior and posterior elevation values, were all higher in JIA-U patients. Endothelial cell density and morphology, on the other hand, did not differ significantly between groups. Chronic inflammation's impact on stromal remodelling could explain these corneal alterations. The positive correlation between posterior elevation and the number of flares and duration of inflammation represents the importance of early diagnosis and effective treatment.

Corneal thickness measurements with the RTVue, Casia-2, and Pentacam devices in patients with mild-to-moderate keratoconus: a comparative study

BACKGROUND

To compare the characteristics of corneal thickness measurements among the RTVue, Casia-2, and Pentacam in patients with mild-to-moderate keratoconus.

METHODS

We recruited 46 eyes of 46 patients diagnosed with mild-to-moderate keratoconus at our hospital between January and March 2022. The central corneal thickness (CCT) and thinnest corneal thickness (TCT) were measured using two optical coherence tomography (OCT) instruments (RTVue and Casia-2) and the more conventional Pentacam. Differences and correlations between the CCTs and TCTs, based on the device and influencing factors, were explored.

RESULTS

The CCTs were highly consistent among the groups (p = 0.434) and correlated with one another (p < 0.001). The TCTs measured by OCTs were thinner than those measured by the Pentacam (p < 0.001); however, all three devices were highly correlated (p < 0.001). The thinnest point location measurements with RTVue and Casia-2 differed significantly from the measurements with the Pentacam. Bland-Altman plots demonstrated a significant agreement between Pentacam and OCTs in TCT measurement (p < 0.001); the 95% limits of agreement were - 3.1 μm to + 33.1 μm for Pentacam and RTVue and - 8.6 μm to + 36.5 μm for Pentacam and Casia-2. RTVue and Casia-2 showed no difference in corneal thickness (p = 0.633) and thinnest point location measurement (p > 0.05). Multivariate analysis identified that the TCT measurement difference between the RTVue and Pentacam was related to the difference between the CCT and TCT (b = 0.490, 95% confidence interval [CI]: 0.033 to 0.948, p = 0.036), whereas the difference between the Casia-2 and Pentacam was related to the anterior radius for curvature (A) grade (b = 3.9, 95% CI: 1.753 to 6.074, p = 0.001), corneal pachymetry at the thinnest (C) grade (b = - 7.875, 95% CI: - 11.404 to - 4.346, p < 0.001), and the difference between the CCT and TCT (b = 0.425, 95% CI: 0.1 to 0.751, p = 0.012).

CONCLUSIONS

CCTs in patients with mild-to-moderate keratoconus were similar among all three devices, but the TCTs and the thinnest point locations were not. Furthermore, the TCT measurement differences between the OCT devices and the Pentacam were more pronounced in keratoconus cases with a steeper anterior surface, thicker TCTs, and a larger difference between the CCT and TCT.

TRIAL REGISTRATION

Number: 2021118-1. Retrospectively registered: September 01, 2021.

Real-time corneal thickness changes during phacoemulsification cataract surgery

PURPOSE

To observe the changes in corneal thickness during phacoemulsification cataract surgery and to analyze the influencing factors.

METHODS

One hundred two patients (102 eyes) with cataracts undergoing phacoemulsification cataract surgery at Shandong Eye Hospital between July and October 2021 were included. Intraoperative OCT was applied to capture real-time images preoperatively, before and after ultrasonic emulsification, at the end of irrigation aspiration and the end of surgery. Then, the corneal thickness at the above time points was measured using Photoshop software.

RESULTS

The corneal thickness of 102 cataract patients was 511.79 ± 31.46 μm before operation and 512.71 ± 31.51 μm at the beginning of phacoemulsification, which increased by 0.91 ± 1.48 μm (0.2%). At the end of ultrasonic emulsification, the corneal thickness was 521.58 ± 32.75 μm and 8.87 ± 8.71 μm (1.7%) thicker than that before the procedure. After irrigation aspiration, the corneal thickness reached 528.09 ± 33.87 μm, which increased by 6.52 ± 6.38 μm (1.3%) compared with that of the previous step. At the end of the operation, the corneal thickness was 539.19 ± 33.88 μm, 11.09 ± 10.92 μm, and 27.37 ± 13.64 μm thicker than that of the previous step and the preoperative thickness, respectively, with an overall increase of 5.3%. The differences were statistically significant at all time points (all P < 0.001). Correlation analysis showed that postoperative corneal thickness changes were correlated with age, cataract lens nuclear grade, actual phacoemulsification time (APT), effective phacoemulsification time (EPT), average phacoemulsification energy (APE), total surgery time (TST), cell density (CD), maximum cell area (MAX), and cell area standard deviation (SD) (all P < 0.05), while the changes in thickness were not correlated with gender, cell area coefficient of variation (CV), percentage of hexagonal cells (6A), average cell area (AVE), or minimum cell area (MIN) (all P > 0.05).

CONCLUSIONS

During phacoemulsification cataract surgery, corneal thickness gradually increases in real time with the increase of perfusion pressure and intraocular manipulation time. The real-time magnitude of intraoperative corneal thickness change is closely related to lens nucleus hardness, corneal endothelial cell density, ultrasound energy, and time for emulsification.

Comparison of Postoperative Safety, Efficacy, and Visual Quality after SMILE for Myopic Patients with Different Corneal Thicknesses

PURPOSE

To investigate the safety, efficacy, and visual quality of small incision lenticule extraction (SMILE) in different corneal thickness patients with myopia or myopic astigmatism.

METHODS

This prospective cohort study included 191 right eyes of 191 patients. Eyes were divided into three groups according to preoperative central corneal thickness (CCT) (Preoperative central corneal thickness (CCT) was the group indicator.) There were 31 eyes in the thin cornea group (CCT ≤500 um (μm), TC), 94 eyes in the moderate corneal thickness group (CCT ≥501 um (μm) and ≤550 um (μm), MD) and 66 eyes in the thick cornea group (CCT ≥550 um (μm), TK). Comparisons in uncorrected (UDVA) and best-corrected distance visual acuity (BDVA), manifest refractive spherical equivalent (SE), preoperative mesopic/photopic contrast sensitivity (CS), ocular higher-order aberrations (HOAs) at a 6mm analytical pupil diameter, and visual quality questionnaires were made (performed) among the three groups during the postoperative six months. Subgroup analyses were made based on preoperative SE.

RESULTS

The safety indices at six months were 1.15 ± 0.18, 1.14 ± 0.17, and 1.18 ± 0.17, respectively (p = 0.374), and the efficacy indices at six months were 1.07 ± 0.25, 1.12 ± 0.22, and 1.11 ± 0.21, respectively (p = 0.599). The postoperative SE was -0.07 ± 0.52D, -0.14 ± 0.38D, and -0.05 ± 0.46D after SMILE in the three groups, respectively (p = 0.376). No significant difference was found in mesopic/photopic CS, HOAs, and visual quality among different corneal thickness groups and SE groups. Postoperative SE and efficacy indices were the lowest in thin cornea eyes with ultra-high myopia (over -9.00 D).

CONCLUSIONS

SMILE provides comparable safety, efficacy, and visual quality results in different corneal thickness patients. Those with myopia higher than -9.00 D had less efficacy after surgery, especially in thin cornea patients.

Corneal Biometric Features and Their Association With Axial Length in High Myopia

PURPOSE

To characterize the morphologic features of corneal parameters and their correlation with axial length (AL) elongation in patients with high axial myopia.

DESIGN

Cross-sectional comparative study.

METHODS

A total of 299 eyes with high myopia (299 patients) and 266 eyes of age- and sex-matched control subjects (266 patients) were examined by anterior segment swept-source optical coherence tomography (SS-OCT) and an IOL Master. Central corneal thickness (CCT), thinnest corneal thickness (TCT), corneal volume (CV), and anterior corneal curvature (CC), posterior CC, and total CC were obtained, and their correlation with AL was investigated using multiple linear regression model.

RESULTS

The CCT, TCT, CV, and anterior, posterior, and total CC of patients with high myopia were smaller than those of the control subjects. The CCT, TCT, and CV had a continuous downward trend with AL. However, CC decreased rapidly with AL when AL was <26 mm and the slope decreased when AL was 26 to 28 mm. This linear association was absent when AL was >28 mm. Multiple linear regression showed that the CCT (β = -1.98, P = .007), TCT (β = -1.63, P = .019), and CV (β = -0.13, P = .001) were associated with AL. Anterior, posterior, and total CCs were negatively associated with AL when AL was <26 mm (all P < .001) and when AL was between 26 and 28 mm (all P < .05).

CONCLUSIONS

CC decreases may serve as a refractive compensation on myopia when AL is <28 mm. However, this effect does not exist when AL is >28 mm. Consideration should be given to the special distribution of cornea curvature for IOL calculations in subjects with high myopia.

Five-year follow-up of corneal morphology and corneal refractive power changes after uneventful DMEK

PURPOSE

To investigate changes of corneal thickness spatial profile (CTSP), corneal volume (CV) distribution, and total corneal refractive power (TCRP) over a course of 60 months after uneventful Descemet membrane endothelial keratoplasty (DMEK).

METHODS

In our prospective, comparative study, sixty DMEK cases without intraoperative and postoperative complications and with complete 60-month follow-up were included (group 1). CTSP at corneal apex (CCT) and at 2 mm, 4 mm, 6 mm, and 8 mm rings, CV in 3 mm, 5 mm, 7 mm, and 10 mm zones, and TCRF in 2 mm, 4 mm 6 mm, and 8 mm zones were evaluated preoperatively and at 3, 6, 12, 24, and 60 months postoperatively. The 60-month results were compared to an age-matched group of uncomplicated pseudophakic eyes (group 2; n = 20).

RESULTS

The CCT and CTSP at 2, 4, and 6 mm increased significantly at 60 months compared to 3-month outcomes (P < 0.001). Similarly, CV increased significantly in 3 mm, 5 mm, and 7 mm zones at 60 months compared to 3 months outcomes (P < 0.001). The TCRP showed in all zones a significant decrease at 3 months (P < 0.001) followed by a continuous and significant increase at 60 months (P < 0.001). The 60-month CCT and CTSP at 2 mm were similar to group 2 (P ≥ 0.094).

CONCLUSION

Sixty months after uneventful DMEK, CT within the central 2 mm zone and CV at 3 mm zone were similar to uncomplicated pseudophakic eyes. A continuous and statistically significant increase of TCRP was observed in all measured zones after the 3-month examination.

Predictive factors of the accelerated transepithelial corneal cross-linking outcomes in keratoconus

Background

This study aimed to evaluate the clinical outcomes and assess preoperative characteristics that may predict outcomes in keratoconus 1 year after accelerated transepithelial corneal cross-linking (ATE-CXL).

Methods

This prospective study included 93 eyes of 84 consecutive keratoconus patients with 1-year follow-up after ATE-CXL. Preoperative characteristics included corneal astigmatism, anterior chamber depth, anterior chamber volume, radius of curvature, posterior elevation, central corneal thickness (CCT), thinnest corneal thickness, steepest meridian keratometry, flattest meridian keratometry, and the maximum keratometry (Kmax). Data were obtained preoperatively and at 1, 3, 6, and 12 months postoperatively. The patient eyes were grouped into 3 subgroups according to CCT and Kmax values to observe the changes of keratoconus progression.

Results

All patients were successfully operated without complications at any follow-up time point. Mean changes of Kmax from baseline at 6 and 12 months were − 0.60 ± 2.21 D (P = 0.011) and − 0.36 ± 1.58 D (P = 0.030), respectively. Eyes with a thinner CCT and higher Kmax values exhibited a tendency for topographic flattening of ≥1.0 D (P = 0.003; P = 0.003). In the subgroup comparison, the Kmax values decreased significantly at 6 and 12 months after ATE-CXL in the group with CCT ≤ 450 μm (P = 0.018 and P = 0.045); the Kmax values of the group with Kmax > 65.0 D decreased significantly at 6 months postoperatively (P = 0.025).

Conclusion

ATE-CXL is a safe and effective treatment for keratoconus patients. Patients with thinner CCT and higher Kmax values are more likely to benefit from ATE-CXL.

Differences and Limits of Agreement among Pentacam, Corvis-ST, and IOL-Master 700 Optical Biometric Devices regarding Central Corneal Thickness Measurements

Purpose:

To investigate the differences and limits of agreement in measuring corneal thickness using Pentacam, Corvis, and intraocular lens (IOL)-Master 700 devices.

Methods:

This study was conducted on 37 right eyes of 21 males and 16 females (n = 37) with a mean age of 52.11 ± 6.30 years. The central corneal thickness was measured using three optical biometric devices, including Pentacam, Corvis, and IOL-Master 700. The inclusion criteria were normal eyes without any ophthalmological abnormalities, history of ocular pathology, or ocular surgery. The data obtained from these three devices were compared two by two. The correlation and agreement limits among them were analyzed using statistical techniques.

Results:

The mean standard deviation differences between Pentacam and Corvis, Pentacam and IOL-Master 700, as well as Corvis and IOL-Master 700 regarding the corneal thickness measurement, were 22.13 ± 8.05, 7.91 ± 8.02, and 14.21 ± 9.85 μm, respectively, which were statistically significant (P < 0.0001). Based on the investigation of the limits of agreement according to the Bland Altman method, the corresponding values between Pentacam and Corvis, Pentacam and IOL-Master 700, and Corvis and IOL-Master 700 were -16.2 to +15.4, -15.8 to +16.3, and -20.1 to +20.0 μm, respectively. Furthermore, the correlation coefficients of the measurements obtained by Pentacam and Corvis, Pentacam and IOL-Master 700, as well as Corvis and IOL-Master 700 were determined 0.957, 0.964, and 0.948, respectively (P < 0.0001).

Conclusion:

The results from this study indicate that the interchangeable use of these three devices is not appropriate due to statistically significant differences and broad limits of agreement among the three devices, especially between Corvis and IOL-Master 700.

Changes in Corneal Morphology with Age in Asian Population: A Multicenter Study of 30,618 Cases

Introduction

To evaluate normal reference ranges for corneal morphological parameters and investigate age-related changes in these parameters in Asian subjects with healthy eyes in order to provide reference data for preoperative evaluation of corneal refractive surgery and the early differential diagnosis of subclinical and asymptomatic keratoconus.

Methods

This cross-sectional, multicenter, observational study was conducted in five provinces of China, from January 2014 through October 2019. It is a retrospective analysis. Examiner-blinded clinical measurements were performed after stratification of the subjects into the following age groups: < 18, 18–30, 31–40, 41–50. We evaluated 30,618 healthy eyes of Chinese subjects who exhibited a normal corneal morphology, had no history of eye surgery or trauma, stopped wearing soft contact lenses for at least 2 weeks (rigid contact lenses for at least 4 weeks), and underwent topographic studies for both eyes on the same day.

Results

While the anterior and posterior corneal curvatures (K1 and K2) increased with age, corneal astigmatism of the anterior and posterior surfaces (ΔK) and central, minimum, and overall corneal thicknesses decreased with age. Age-related decrease of the overall corneal thickness was more obvious toward the periphery. The anterior and posterior corneal surface heights exhibited a decrease and an increase, respectively. Both index of height asymmetry (IHA) and index of vertical asymmetry (IVA) exhibited an increase with age.

Conclusions

The cornea exhibits overall thinning with age and gradually changes from a flat ellipse to an elongated ellipse in Asian individuals with healthy eyes. However, the anterior and posterior surfaces become smoother with age. Owing to the very large number of cases, these small differences are statistically significant. The results obtained are consistent with the hypothesis that a normal cornea seems to withstand quite well the effect of IOP, external pressures, and the natural cross-linking.

[Prospective Study on Corneal Safety Evaluation of Children/Adolescents with Low and Moderate Myopia after Long-Term Orthokeratology]

OBJECTIVE

To observe the possible changes in the integrity of the cornea and corneal endothelial cells of children/adolescents with low or moderate myopia after long-term wearing of orthokeratology (ortho-k) lenses, as well as the time when the relevant changes occur, so as to evaluate the safety of long-term wearing of ortho-k lens and to provide a reference for the safety evaluation of subjects wearing ortho-k lenses.

METHODS

Subjects were recruited in the Contact Lens Clinic, West China Hospital, Sichuan University for a three-year prospective study. Ortho-k of the same brand was matched for the subjects. The central corneal thickness (CCT), corneal endothelial cell density (ECD), and hexagonal cell ratio (HEX) were measured prior to the wearing of ortho-k lenses and after wearing ortho-k lenses for 1 month, 3 months, 6 months, and every 3 months until 36 months. The results of corneal fluorescence staining were recorded during each follow-up. When corneal staining was observed, the Efron grading standard was used for grading and corresponding treatment was given.

RESULTS

A total of 33 (66 eyes) myopic patients were included in the study. 15 cases (46.2%) reported having binocular foreign body sensations and tearing within the first week of wearing the lenses. After the subjects became adapted to wearing the lenses, the symptoms disappeared without intervention. During the follow-up period, 31 cases (93.94%) of binocular corneal staining were observed, of which, 24 cases (72.73%) were graded as G0, receiving no treatment, 5 cases (15.15%) were graded as GⅠ, and 2 cases (6.06%) were graded as GⅡ. Corresponding clinical treatment for corneal staining was given to the GⅠ and GⅡ subjects. This study found that the corneal ECD was inversely proportional to age ( r=－0.380, P=0.002). During the three-year follow-up period, the subjects' left eye ECD decreased from the baseline at 24 months and the right eye ECD decreased from the baseline at 27 months ( P<0.05). The CCT results in the subjects showed that CCT became thinner at 1 month after wearing the lens ( P<0.05), but the follow-up CCT showed a stable trend.

CONCLUSION

After three years of long-term follow-up, no serious corneal complications occurred in children/adolescents with moderate and low myopia after long-term wearing of ortho-k lens. The corneal ECD of both eyes started decreasing 24 months after wearing the ortho-k lenses and the CCT decreased 1 month after wearing the lenses.

Mendelian randomization analysis identified genes pleiotropically associated with central corneal thickness

OBJECTIVE

To prioritize genes that were pleiotropically or potentially causally associated with central corneal thickness (CCT).

METHODS

We applied the summary data-based Mendelian randomization (SMR) method integrating summarized data of genome-wide association study (GWAS) on CCT and expression quantitative trait loci (eQTL) data to identify genes that were pleiotropically associated with CCT. We performed separate SMR analysis using CAGE eQTL data and GTEx eQTL data. SMR analyses were done for participants of European and East Asian ancestries, separately.

RESULTS

We identified multiple genes showing pleiotropic association with CCT in the participants of European ancestry. CLIC3 (ILMN_1796423; PSMR = 4.15 × 10- 12), PTGDS (ILMN_1664464; PSMR = 6.88 × 10- 9) and C9orf142 (ILMN_1761138; PSMR = 8.09 × 10- 9) were the top three genes using the CAGE eQTL data, and RP11-458F8.4 (ENSG00000273142.1; PSMR = 5.89 × 10- 9), LCNL1 (ENSG00000214402.6; PSMR = 5.67 × 10- 8), and PTGDS (ENSG00000107317.7; PSMR = 1.92 × 10- 7) were the top three genes using the GTEx eQTL data. No genes showed significantly pleiotropic association with CCT in the participants of East Asian ancestry after correction for multiple testing.

CONCLUSION

We identified several genes pleiotropically associated with CCT, some of which represented novel genes influencing CCT. Our findings provided important leads to a better understanding of the genetic factors influencing CCT, and revealed potential therapeutic targets for the treatment of primary open-angle glaucoma and keratoconus.

Multimodal ocular evaluation in hemodialysis patients

PURPOSE

To evaluate choroidal thickness, intraocular pressure (IOP), axial length, central corneal thickness (CCT), lens thickness, anterior chamber depth, and ocular pulse amplitude (OPA) in hemodialysis patients.

MATERIALS AND METHODS

The patients with end-stage renal disease and undergoing hemodialysis were included in the study. Immediately before and 1 hour after hemodialysis, all patients underwent measurement of choroidal thickness with spectral domain optical coherence tomography (SD-OC, Cirrus HD-OCT; Carl Zeiss Meditec Inc., Dublin, CA), IOP and OPA with Pascal dynamic contour tonometry (Ziemer Ophthalmic Systems AG, Port, Switzerland), and anterior chamber depth, lens thickness, and axial length with optical biometry (LenStar LS900; Haag-Streit AG, Koeniz, Switzerland). Data from the patients' right eyes were included in the statistical analysis.

RESULTS

The patient group included 8 (36.4%) males and 14 (63.6%) females with a mean age of 56, 14 ± 9, 96 (40-70) years. The mean subfoveal choroidal thickness before and after hemodialysis was 255.21 ± 6.15 (245-263) µm and 234.95 ± 7.89 (220-247) µm, respectively (p < 0.001). Mean choroidal thickness at 1500 µm and 3000 µm nasal and temporal of the fovea also decreased significantly after hemodialysis (p < 0.001). Mean OPA values before and after hemodialysis were 2.14 ± 1.07 (0.6-4) mmHg and 1.6 ± 0.86 (0.5-3.2) mmHg, respectively (p < 0.001). There was a statistically significant correlation between OPA and choroidal thickness measurements (p < 0.001, R = 0.923). IOP increased from 15.11 ± 2.58 (11-20) to 15.99 ± 2.21 (13-20) mmHg, but the change did not reach statistical significance (p = 0.05). There was no statistically significant change in mean axial length, anterior chamber depth, lens thickness, or CCT after hemodialysis (p > 0.05 for all).

CONCLUSION

Although choroidal thickness and OPA may be decreased immediately after hemodialysis, there may be no significant changes in IOP or avascular ocular structures such as the lens and cornea.

[Pachymetry with a video slit lamp]

BACKGROUND AND OBJECTIVE

Presentation and application of a method for pachymetry with the slit lamp based on the concept of a defined optical section.

METHODS AND PATIENTS

The visible width of an optical section on slit lamp examination with a 45° angle between the slit beam and the central corneal surface was determined in 103 eyes (68 with glaucoma and 35 in patients with keratoconus). The measurements were compared to the pachymetric values previously determined elsewhere for these eyes in order to establish a proportionality factor for calculation of corneal thickness from slit lamp measurements.

RESULTS

From a linear regression between the external pachymetry and visible width of the optical section in the split lamp, 1.71 was determined to be the factor of proportionality. Applying this factor to single measurements, 82 out of 103 eyes had a maximum difference of 40 µm compared to the external pachymetric values.

CONCLUSION

Based on a defined optical section at the slit lamp, clinically relevant estimates can be made for central corneal thickness in diseases, such as glaucoma or keratoconus. The difference to the externally measured pachymetric values was within the range of diurnal changes in corneal thickness for 80% of the eyes. Similar to other pachymetric procedures, the reliability of determination of the corneal thickness with the slit lamp also increases when applied intraindividually or for the same eye in the course of time.

Relationship between corneal biomechanical parameters and corneal sublayer thickness measured by Corvis ST and UHR-OCT in keratoconus and normal eyes

BACKGROUND

To explore the relationship between corneal biomechanical parameters and corneal sublayer thickness using corneal visualization Scheimpflug technology (Corvis ST) and ultrahigh-resolution optical coherence tomography (UHR-OCT) in clinical and suspected keratoconus and normal eyes.

METHODS

Cross-sectional prospective study. A total of 94 eyes of 70 participants were recruited. Twenty five eyes of 19 keratoconus patients, 52 eyes of 34 patients showing high risk of developing keratoconus according to the Belin/Ambrosio Enhanced Ectasia Display, and each eye of 17 normal subjects were enrolled. All participants underwent Corvis ST, Pentacam, and UHR-OCT examinations at the same time. Stiffness parameter A1 (SP-A1), deformation amplitude ratio (DA ratio), and other biomechanical parameters were recorded using Corvis ST. The vertical and horizontal thickness profiles of central 3 mm corneal epithelium, Bowman's layer, and stroma as measured by the perpendicular distance between the neighboring interfaces were generated using UHR-OCT. The flat keratometry and steep keratometry were obtained using Pentacam. Analysis of correlation was applied to explore the association between variables.

RESULTS

Most of the biomechanical parameters and corneal sublayer thickness profiles showed statistical differences among three groups. A statistically significant linear relationship was noted between SP-A1 and DA ratio in all three groups. SP-A1 was found to be positively correlated with epithelial and Bowman's layer thickness in the keratoconus (KC) group, and with stromal thickness in all three groups. In the normal and suspected keratoconus (SKC) groups, only stromal thickness was included in the stepwise linear regression to predict SP-A1, whereas in the KC group, steep keratometry and Bowman's layer thickness were included.

CONCLUSIONS

Significant and different correlations were noted between corneal stiffness and corneal sublayer thickness in different groups, indicating that corneal sublayers may play different roles in maintaining corneal biomechanical stability between keratoconus and normal eyes.

Repeatability and agreement of corneal thickness measurements by three methods of pachymetry in small incision lenticule extraction eyes

Background: The accurate evaluation of corneal thickness (CT) post small incision lenticule extraction (SMILE) is clinically relevant to reduce the risk of complications. We aimed to analyze repeatability and agreement of central corneal thickness (CCT), thinnest corneal thickness (TCT), and mid-peripheral corneal thickness (MPCT) measurements using Scheimpflug imaging, anterior segment swept-source optical coherence tomography (AS-SS-OCT, CASIA 1000, Tomey), and ultrasound pachymetry (USP, SP-3000, Tomey) in eyes with previous SMILE. Methods: Ninety-one eyes of 91 patients were included. Within-subject standard deviation (Sw), test-retest repeatability (TRT), intraclass correlation coefficient (ICC), and coefficient of variation (CoV) were used to evaluate repeatability. Agreement was assessed by repeat-measurement analysis of variance and Bland-Altman analysis. Results: The above three instruments revealed that Sw was <5.91 µm, CoV was <1.08%, TRT was <16.38 µm, and ICC was >0.94. The 95% limits of agreement were relatively narrow and Bland-Altman plots were more concentrated at the CCT, at the TCT, and at the CT_2mm. However, it was shown to be wide at the CT_5mm. Conclusions: The three devices provide good repeatability of CT measurements in patients who undergone SMILE. Agreement between measurements at the CCT, TCT, and CT_2mm were high, but measurement agreements among CT_5mm revealed poor agreement.

Myopia Prevalence and Ocular Biometry Features in a General Japanese Population: The Nagahama Study

PURPOSE

To describe the distribution of ocular biometry and refraction in Japanese adults.

DESIGN

Cross-sectional analysis of a prospective cohort study.

PARTICIPANTS

A total of 9850 individuals participated in the first follow-up of the Nagahama Prospective Cohort for Comprehensive Human Bioscience (the Nagahama Study) conducted between 2013 and 2016. Participants were between 34 and 80 years of age.

METHODS

All participants underwent axial length (AL; in millimeters), anterior chamber depth (ACD; in millimeters), corneal diameter (white to white; in millimeters), and central corneal thickness (CCT; in micrometers) measurement (IOL Master; Carl Zeiss Meditec, Dublin, CA) and refraction (spherical equivalent [SE]; in diopters [D]) and corneal curvature (CC; in millimeters) measurement (ARK-530A; Nidek, Aichi, Japan). Distribution of these ocular biometric parameters and prevalence of myopia, high myopia, and extreme myopia were summarized.

MAIN OUTCOME MEASURES

Distribution of ocular biometry and refraction.

RESULTS

After standardization to the national population of 2015, estimates of mean AL and SE were 24.21 mm and -1.44 D, respectively. Estimates of mean CC, corneal diameter, CCT, and ACD were 7.69 mm, 12.01 mm, 543.96 μm, and 3.21 mm, respectively. After standardization of age and gender, the prevalence of myopia (SE, ≤-0.5 D) and high myopia (SE, ≤-6.0 D) were 49.97% and 7.89%, respectively. Approximately 70% of the younger participants (34-59 years of age) showed myopia, whereas high myopia was observed in approximately 10%. Although the number of individuals with myopia or high myopia was higher in the younger age groups, the prevalence of more extreme phenotypes remained stable across all ages, especially in women. Axial length of more than 30 mm was observed only in older women (n = 5 [0.05%]).

CONCLUSIONS

We showed detailed distributions of various ocular biometry and refraction parameters using a large general Japanese cohort. Prevalences of myopia and high myopia from 2013 through 2016 were higher than those in earlier studies, which reflects recent environmental change. However, constant prevalence of extreme myopia across all ages suggests high genetic predisposition of the extreme phenotype.

Reduction of corneal epithelial thickness during medical treatment for myopic regression following FS-LASIK

Background

To evaluate corneal epithelial thickness change during medical treatment for eyes with myopic regression after femtosecond laser-assisted in situ keratomileusis (FS-LASIK).

Methods

This study included 84 eyes of 54 subjects diagnosed with myopic regression after FS-LASIK and treated using topical steroid and anti-glaucoma drugs. Corneal epithelial thickness was measured using Fourier-domain optical coherence tomography before and after treatment. Subjects were divided into three groups based on their corneal epithelial thickness at the time of myopic regression and regression analyses were used to investigate the association between corneal epithelial thickness, visual acuity, and refraction. Logistic regression and receiver operating characteristic (ROC) curve analysis was performed to determine whether corneal epithelial thickness could predict the success of treatment, improvements of ≥ two lines in uncorrected distance visual acuity and ≥ 0.5 diopter in refraction or K.

Results

Corneal epithelial thickness decreased with greater change in the center as myopic regression subsided during medical treatment. Subgroup with the thickest epithelium (≥ 62 μm) showed a higher success rate and greater changes in refraction and vision. Reduced magnitude of corneal epithelial thickness showed significant correlations with changes of K and refractive error (all P < 0.001). Corneal epithelial thickness was a significant factor for the success of treatment and ROC curve showed that corneal epithelial thickness > 60.50 μm had 81.5% sensitivity and 84.2% specificity for the success of medical treatment.

Conclusion

Corneal epithelial thickness decreases proportionally with the magnitude of improvement of myopic regression during treatment with steroid and anti-glaucoma drugs in post-LASIK eyes with myopic regression.

Agreement of Central Corneal Thickness Measurements between Scheimpflug Photography and Optical Low-Coherence Reflectometry in Children

PURPOSE

Central corneal thickness (CCT) is a key indicator of the corneal health status and is therefore of clinical importance. The aim of the present study was to determine the agreement between Scheimpflug photography (SP) and optical low-coherence reflectometry (OLCR) systems in measuring the CCT in children.

METHODS

In this cross-sectional study, the samples were selected from Shahroud schoolchildren using cluster sampling. The samples then underwent optometric examinations, including the measurement of visual acuity and refraction. CCT measurements were done by the SP and OLCR systems between 8 am and 4 pm. To evaluate the agreement between these devices, 95% limits of agreement (LoA) and interclass correlation coefficient (ICC) were reported.

RESULTS

After applying the exclusion criteria, 4890 right eyes (53.2% male) were analyzed. The mean age of the students was 9.22 ± 1.72 years (range: 6-12 years). The mean CCT by the SP and OLCR systems was 555.30 ± 34.15 and 550.23 ± 35.11 µm, respectively. The 95% LoA between the two devices was -19.81 to 9.66 µm, and the ICC was 0.983. The CCT difference between the SP and OLCR systems was 5.61 µm in boys and 3.36 µm in girls. The CCT difference between the two devices was 6.41 µm in 6-year-old and 3.54 µm in 12-year-old children. The 95% LoA was -17.96 to 9.58 µm and -18.89 to 8.47 µm and the ICC was 0.987 and 0.984 in myopic and hyperopic subjects, respectively.

CONCLUSION

The results of this study showed a high agreement between OLCR and SP measurements of CCT in children.

Measurement of central corneal thickness using Orbscan 3, Pentacam HR and ultrasound pachymetry in normal eyes

PURPOSE

To assess the agreement between Orbscan 3, Pentacam HR and ultrasound pachymetry (Palm Scan AP 2000) in measuring central corneal thickness.

METHODS

Prospective observational cross-sectional study of ninety-two eyes of 48 patients with normal corneas was conducted. Central corneal thickness was measured via Pentacam HR, Orbscan 3 and ultrasound pachymetry. Bland-Altman analysis was used to demonstrate agreement between various methods.

RESULTS

Ninety-two eyes of 46 subjects were enrolled. The mean age was 29.67 years (18-59). The average measurements of central corneal thickness were 545.73 ± 29.35 μm, 549.34 ± 29.14 μm and 545.78 ± 31.48 μm for the Pentacam HR, Orbscan and ultrasound pachymetry, respectively. The three devices measurements are closely correlated, with Pearson correlation coefficient ranging from 0.868 to 0.929. The 95 % limits of agreement were 25.2 to - 18 μm between Orbscan and Pentacam central corneal thickness, 25.2 to - 25.7 μm between Pentacam and pachymetry central corneal thickness and 34.4 to - 27.2 μm between Orbscan and pachymetry central corneal thickness.

CONCLUSION

In spite of advancement of Orbscan 3, still there are wide agreement limits between CCT measurements obtained via Orbscan 3, Pentacam HR and ultrasound pachymetry; thus, interchangeable use in clinical practice is not recommended.

Anterior segment parameters in Behçet's patients with ocular involvement

PURPOSE

To evaluate anterior segment findings in Behçet's disease patients within the ocular involvement inactive period.

METHODS

One hundred twenty patients with Behçet uveitis in the inactive period (Behçet's disease group) and 121-age and sex matched healthy subjects (control group) were examined. Anterior segment parameters were assessed by Scheimpflug camera.

RESULTS

In Behçet's disease group, the mean age was 39.89 ± 10.16 years, and 55.8% of patients were male; in the control group, the mean age was 38.69 ± 14.08 years, and 56.2% of control subjects were male. Pachymetric measurements of corneal apex (523.84 ± 30.36 µ vs 540.73 ± 27.85 µ, p < 0.001) thinnest point (518.70 ± 30.75 µ vs 537 ± 28.66 µ, p < 0.001), mean corneal volume (57.90 ± 3.39 mm³ vs 59.57 ± 3.37 mm³, p < 0.001) were significantly lower and anterior elevation [5.0 (1.0-34.0) vs 2.0 (1.0-7.0) diopter(D), p < 0.001], posterior elevation [11.0 (1.0-66.0) vs 4.0 (0-22.0) D, p < 0.001)] and corneal astigmatism [1.1 (0-7.1) vs 0.7 (0.1-5.7) D, p = 0.005] were significantly higher in the Behçet's disease group than in control group. No significant difference was found in other anterior segment parameters between the Behçet's disease group and control group. Concurrent keratoconus was detected in two cases (1.7%). A statistically significant correlation was found between the corneal measurements and frequency of uveitis attacks.

CONCLUSION

The chronic inflammatory process associated with various proinflammatory cytokines, which play a role in the pathogenesis of keratoconus, may also contribute to a decrease in corneal thickness and corneal volume in Behçet's patients with ocular involvement.

Anterior segment optical coherence tomography scanning protocols and corneal thickness repeatability

PURPOSE

To examine the influence of anterior segment optical coherence tomography imaging protocols on the intraobserver and intrasession repeatability of epithelial, stromal, and total corneal thickness measurements.

METHODS

Repeated anterior segment optical coherence tomography (AS-OCT) images (Spectralis, Heidelberg) were obtained from 15 adults using single 8.3 mm wide horizontal line scans with an average of 2, 10, 20, 30, 50 and 100 B-scans. Volumetric scans consisting of nine 8.3 mm horizontal line scans encompassing a 1.3 mm vertical region were also captured (with 20 B-scans per line scan). Single point thickness measures (at the normal to the tangent of the anterior corneal surface) were compared with thickness measures averaged over the central 6 mm. The impact of B-scan averaging and intraobserver variability were examined for single line scans. For volumetric scans, the impact of the number of line scans upon intraobserver and intrasession variability were calculated.

RESULTS

Intraobserver repeatability did not vary significantly as a function of the number of averaged B-scans per line scan, but was lowest for 20-30 averaged B scans. For volumetric scans, increasing the number of line scans did increase scan duration (p < 0.001), with minimal impact upon the average scan quality index (p = 0.06). Averaging more than 3 line scans did not significantly improve intraobserver or intrasession repeatability for either single point or average thickness measurements.

CONCLUSION

AS-OCT volumetric scans with 3 lines each consisting of 20 B-scans with measurements averaged over a central 6 mm of the cornea provide highly repeatable measures of epithelial, stromal and total corneal thickness (95 % LoA ≤ ±3.2 μm for intraobserver repeatability and ≤ ±3.7 μm for intrasession repeatability). This scanning protocol can provide reliable information when monitoring subtle changes in corneal thickness.

Effect of short-term orthokeratology lens or ordinary frame glasses wear on corneal thickness, corneal endothelial cells and vision correction in adolescents with low to moderate myopia

Background

We aimed to investigate the effect of short-term orthokeratology lens or frame glasses wear on corneal thickness, corneal endothelial cells and vision correction in adolescents with low to moderate myopia.

Methods

Data of 100 adolescents with low to moderate myopia were retrospectively analyzed. The patients were assigned into two groups. The experimental group were treated with night-wear orthokeratology lens, and control group were treated with ordinary frame glasses. Follow up was carried out at the 3rd, 6th and 12th months of treatment. The naked-eye vision, diopter, corneal curvature, intraocular pressure, axial length, endothelial cell count and central corneal thickness were examined. Complications within 12 months were observed, and corneal fluorescein staining was graded.

Results

The naked-eye vision of the experimental group was significantly higher than that of the control group at the 3rd, 6th and 12th months, while the diopter of the experimental group was significantly lower than that of the control group at these time points. The corneal curvature of the experimental group was significantly decreased when comparing with that of the control group at the above 3 time points. The increase of axial length in the experimental group was significantly less than that in the control group at the 6th and 12th months.

Conclusions

Short-term orthokeratology lens wear can effectively improve the naked-eye vision in adolescents with low to moderate myopia without significant impact on the central corneal thickness and corneal endothelial cells. It is a relatively safe method to correct myopia.

Noninvasive evaluation of anterior segment and tear film parameters and morphology of meibomian glands in a pediatric population with hypogonadism

PURPOSE

To compare the meibomian gland (MG), non-invasive tear film break-up time (NITFBUT), anterior segment measurements between healthy children and children with hypogonadism.

METHODS

A total of 80 eyes of 40 children with hypogonadism and 86 eyes of 43 age- and sex-matched healthy subjects were included in the study. The mean keratometry (Km), maximum keratometry (Kmax), central (CCT), thinnest (TCT) and apical (ACT) corneal thicknesses, corneal volume (CV), anterior chamber depth (ACD), irido-corneal angle (ICA), first and average non-invasive NITFBUT, MG loss, morphology of MGs, and MG distortion grade, specular endothelial cell density (CD), coefficient of variation (CoV), and percentage of hexagonal cells (HG) were analysed.

RESULTS

The mean CCT and TCT values were approximately 20 μm lower on average in patients with hypogonadism (p < 0.05). MG loss was present 56.1% of the healthy children, the ratio increased to 81.3% in children with hypogonadism (p < 0.001). The morphology and distortion grade did not show any significant differences between groups (p > 0.05). The mean NITFBUT value were similar between groups (p > 0.05). The mean CD value did not show any significant difference between groups, however it decreased in the hormone replacement therapy (HRT) group (p = 0.005).

CONCLUSIONS

MG loss is a physiological process that is prominent in the condition of sex steroid deficiency, but does not cause tear film alterations in children. Future studies investigating sex and gender effect on the ocular surface system in an age-based fashion are required to clearly communicate influences in the arenas of ocular surface research.

Choroidal thickness in keratoconus

PURPOSE

Keratoconus is an ectatic eye disease characterized by progressive thinning and steepening of the cornea which leads to irregular astigmatism and visual function loss. Determination of choroidal thickness in keratoconus patients may help us to better understand and manage the keratoconus disease. Choroidal thickness may be a potential marker for disease activity in keratoconus patients. In this study, we aimed to determine choroidal thickness in keratoconus patients and compare the results with the age-matched control group.

METHODS

This is a prospective study with a control group. Keratometry and thinnest corneal thickness was measured and recorded in keratoconus patients. Choroidal thickness of all subjects was measured using an optical coherence tomography device (Spectralis OCT, version 6.0, Heidelberg Engineering, Germany) with an enhanced depth imaging mode without pupil dilation. Mean choroidal thickness of keratoconus patients was compared with healthy subjects.

RESULTS

One hundred and sixty eyes of 80 healthy subjects and 160 eyes of 80 keratoconus patients were included in the study. Mean thinnest corneal thickness of the keratoconus patients was 449.7 ± 3.2 microns. Mean corneal keratometry value and cylindrical refraction error in the keratoconus patients were 53.2 ± 0.2 and 3.3 ± 0.1 diopters, respectively. Mean choroidal thickness was 363.9 ± 59.8 and 328.4 ± 67.2 microns in keratoconus patients and healthy subjects, respectively. There was a very significant difference between keratoconus patients and healthy subjects in terms of choroidal thickness (P = 0.000). There was not a statistically significant correlation between choroidal thickness and thinnest corneal thickness in keratoconus patients (P = 0.814).

CONCLUSION

Choroidal thickness was found to be increased in keratoconus patients. Choroidal thickness could potentially become a new clinical marker for disease activity in keratoconus patients.

Comparison of central corneal thickness measurements using different imaging devices and ultrasound pachymetry

Purpose:

To compare central corneal thickness (CCT) measurements obtained by the AL-Scan, Lenstar LS900, Galilei, and ultrasound pachymetry (UP) in normal and cataractous eyes.

Methods:

Eighty eyes of healthy subjects were included in the study. Each subject was assessed by four different methods of measurements using the AL-Scan, Lenstar LS900, Galilei, and UP by a single examiner. To assess the intraobserver repeatability, three consecutive measurements were taken for the AL-Scan.

Results:

The mean CCT [± standard deviation (SD)] for the AL-Scan, Lenstar LS900, Galilei, and UP were 554.6 ± 30.9 μm, 542.9 ± 31.3 μm, 570.7 ± 30 μm, and 552.7 ± 32.8 μm, respectively. The differences between pairs of mean CCT for the methods are statistically significant for the pairs of Galilei–UP, AL-Scan–Galilei, and Lenstar LS900–Galilei. Bland–Altman plots showed that AL-Scan–UP have the closest agreement, followed by Lenstar–UP and AL-Scan–Lenstar. Galilei was found to have the poorest agreement with the other three methods. The intraobserver repeatability of the AL-Scan was very good with an intraclass correlation coefficient (ICC) of 0.980.

Conclusion:

We found that CCT measurements between the AL-Scan–UP, Lenstar LS900–UP, and AL-Scan–Lenstar LS900 showed very strong correlation and comparable agreement. AL-Scan–UP showed the closest agreement and these devices can be used interchangeably in clinical practice. Galilei significantly showed higher value of CCT compared to other methods. It was also observed that the Al-Scan had excellent intraobserver repeatability.

Reproducibility of the measurement of central corneal thickness in healthy subjects obtained with the optical low coherence reflectometry pachymeter and comparison with the ultrasonic pachymetry

Background

Corneal pachymetry is widely used for refractive surgery and follow up in keratoconus, accurate measurement is essential for a safe surgery.

Objective

To assess intraobserver reliability of central corneal thickness (CCT) measurements using optical low-coherence reflectometry (OLCR) technology and its agreement with ultrasonic pachymeter (US).

Method

Randomized and prospective comparative evaluation of diagnostic technology. One randomly healthy eye of subjects was scanned three times with both devices. Intraobserver within-subject standard deviation (Sw), coefficient of variation (CVw) and intraclass correlation coefficient (ICC) were obtained for reliability analysis; for study agreement, data were analyzed using the paired-sample t test and the Bland-Altman LoA method. The mean of three scans of each equipment was used to assess the LoA.

Results

The study enrolled 30 eyes of 30 subjects with average age of 28.70 ± 8.06 years. For repeatability, the Sw were 3.41 and 5.96 µ, the intraobserver CVw was 2 and 4% and ICC 0.991 and 0.988, for OLCR and US respectively. The mean CCT difference between OLCR and US was 8.90 ± 9.03 µ (95% confidence interval: 5.52-2.27 µ), and the LoA was 35.40 µ.

Conclusions

OLCR technology provided reliable intraobserver CCT measurements. Both pachymetry measurements may be used interchangeably with minimum calibration adjustment.

Osteogenesis imperfecta and the teeth, eyes, and ears-a study of non-skeletal phenotypes in adults

Osteogenesis imperfecta (OI) is a disease causing bone fragility; however, it potentially affects all organs with a high content of collagen, including ears, teeth, and eyes. The study is cross-sectional and compares non-skeletal characteristics in adults with OI that clinicians should be aware of when caring for patients with OI.

INTRODUCTION

Osteogenesis imperfecta (OI) is a hereditary connective tissue disorder. The skeletal fragility is pronounced; however, OI leads to a number of extra-skeletal symptoms related to the ubiquity of collagen type 1 throughout the human body. The vast majority of knowledge is derived from studies performed in the pediatric population. Thus, we aimed to investigate the nature and prevalence of ophthalmologic, odontologic, and otologic phenotypes in an adult population with OI.

METHODS

The study population comprises 85 Danish OI patients (age 44.9 ± 15.9 years). Fifty-eight patients had OI type I, 12 OI type III, and 15 OI type IV according to the classification by Sillence. Audiometric evaluations and dental examinations were performed in 62 and 73 patients, respectively. Ophthalmologic investigations were performed in 64 patients, including measurements of the central corneal thickness.

RESULTS

All patients, except two, had corneal thickness below the normal reference value. Patients with OI type I and patients with a quantitative collagen defect had thinner corneas compared to patients with OI type III and other patients with a qualitative collagen defect. One patient in this cohort was diagnosed with and treated for acute glaucoma. Dentinogenesis imperfecta was diagnosed in one fourth of the patients, based on clinical and radiographic findings. This condition was predominately seen in patients with moderate to severe OI. Hearing loss requiring treatment was found in 15 of 62 patients, of whom three were untreated. The most prevalent type of hearing loss (HL) was sensorineural hearing loss, whereas conductive HL was solely seen in patients with OI type III. The patients with the most severe degrees of HL were patients with mild forms of OI. Age was associated with increased HL.

CONCLUSION

Although significant health problems outside the skeleton are frequent in adult patients with OI, the patients are not consistently monitored and treated for their symptoms. Clinicians treating adult patients with OI should be aware of non-skeletal health issues and consider including regular interdisciplinary check-ups in the management plan for adult OI patients.

Intraocular pressure (IOP) measurements in keratoconic patients: Do variations in IOP respect variations in corneal thickness and corneal curvature?

PURPOSE

To explore the relationship between intraocular pressure (IOP) measurements and topographical variations in corneal curvature and corneal thickness in a cohort of keratoconic patients presenting to a newly-established regional Keratoconic diagnostic and monitoring clinic in Northern Ireland.

METHODS

IOP was recorded, using a hand held ICARE tonometer, at central, nasal and temporal locations on keratoconic corneae of 27 consecutive patients attending clinic. Pachymetry and sagittal keratometry were recorded in matched locations using the Pentacam Topographer. Eyes with history of corneal surgery or anterior surface pathology were excluded.

RESULTS

The median (interquartile range) central keratometry, pachymetry (CCT) and IOP measurements for 49 eyes were 44.1D (42.2D-48.1D); 495 μm (460 μm-526 μm); 10 mmHg (8 mmHg-13 mmHg) respectively. Temporal and nasal keratometry, pachymetry, and IOP values, recorded on midline, were temporal 41.9D (40.7D-42.8D); 621 μm (579 μm-650 μm); 14 mmHg (11 mmHg-16 mmHg); nasal 40.8D (39.5D-42.5D); 641 μm (599 μm-698 μm); 13 mmHg (12 mmHg-17 mmHg). A moderate correlation was shown between reduction in CCT and increase in mean central keratometry (Spearman's Coefficient (ρ) -0.72 P = 0.00). A moderate correlation was found between reduction in CCT and reduction in IOP, as recorded centrally (ρ = 0.37 P = 0.01). Mid-peripheral values demonstrated similar trends in the relationship between keratometry and IOP (nasal ρ = -0.47 P = 0.00; temporal ρ = -0.38 P = 0.00) and pachymetry and IOP (nasal ρ = 0.29 P = 0.05; temporal ρ = 0.33 p = 0.02).

CONCLUSION

In this pilot study, a positive correlation exists between pachymetry, keratometry and IOP. Topographically variations in intraocular pressure mimic changes in keratometry and pachymetry.

Corneal Involvement of Patients with Polymyositis and Dermatomyositis

Purpose: To evaluate corneal parameters in patients with polymyositis (PM) and dermatomyositis (DM) and compare them with those of healthy controls.Methods: A total of 43 PM and 32 DM patients and 93 controls were enrolled in this cross-sectional, observational, case-control study. Corneal parameters were evaluated by Pentacam. Objective clinical tests of dry eye disease (DED) were also performed.Results: All pachymetric measurements and corneal volumes (CVs) proved to be significantly lower both in PM and DM patients. The values of DM patients were closer to control values than those of the PM patients. For tear break-up time and Schirmer-I test values significant differences were observed between patients and controls, with values decreased both in PM and DM patients.Conclusions: PM patients rather than DM patients tend to develop thinner and low-volume corneas as compared to controls. Additionally, a high prevalence of DED among both PM and DM patients was also detected.

Comparison of ultrasonic pachymetry and Fourier-domain optical coherence tomography for measurement of corneal thickness in dogs with and without corneal disease

Several ultrasonic and Fourier-domain optical coherence tomography (FD-OCT) pachymeters are used to measure corneal thickness in canine patients and research subjects. This study assessed the reliability of and consistency between two ultrasonic pachymetry (USP) devices, Pachette 3 and Accupach VI, as well as automated and manual measurements obtained using FD-OCT in dogs with and without corneal disease. Corneal thickness measurements were compiled from 108 dogs and analyzed using mixed effects linear regression, with Bonferonni adjustments for post-hoc comparisons, to determine the effects of age, weight and disease state. Data are presented as predicted mean±standard error. Canine corneal disease can result in marked increases in thickness that frequently exceed the upper limits of measurement of some pachymetry devices developed for human use. In this study, the corneas of dogs with endothelial disease or injury frequently exceeded the upper limits of quantitation of 999 and 800μm for the Accupach VI and automated FD-OCT pachymeters, respectively. Using values <800μm, the Pachette 3 generated significantly greater values for central corneal thickness (CCT) than the Accupach VI, manual FD-OCT and automated FD-OCT at 625±7.0, 615±7.2, 613±7.2, and 606±7.4μm respectively (P<0.001). Of the two devices where measurements >1000μm were obtained, manual FD-OCT demonstrated less variability than the Pachette 3. Corneal thickness increased linearly with age and weight with an increase of 6.9±1.8μm/year and 1.6±0.8μm/kg body weight (P<0.005 and P=0.038, respectively).

Criticality of the measurement of corneal thickness in specular reflection by digital biomicroscope

PURPOSE

The aim was to evaluate the effects on corneal thickness (t) measurement, of asymmetry of the CCD position for a digital biomicroscope in specular reflection.

METHODS

t was deduced from the distance between reflexes from anterior and posterior corneal surfaces using a biomicroscope (Takagi SM70 N), with the illuminator either, (a) farther from sensor side (150 eyes) or, (b) closer to it (134 eyes). The distance between reflexes was also measured on a glass slide and a reference lens, with nominal thicknesses of 1580 and 520 μm, respectively. Corneal thickness (t_PACH) was also measured by pachymeter (Canon TX-20 P).

RESULTS

When biomicroscope asymmetry was ignored, t for the glass slide was (a) 1760 and (b) 1404 μm. Correcting for the asymmetry provided corresponding values of 1588 and 1591 μm. For the lens, t was (a) 696 and (b) 543 μm, or 642 and 497 μm, when using the approximation of parallel surfaces (APS). Correcting for the asymmetry gave 565 and 552 μm (578 and 564 μm, with APS). Mean corneal t was (a) 560 and (b) 467 μm, (564 and 468 μm, with APS). Correcting for asymmetry gave (a) 506 and (b) 529 μm (508 and 530 μm, with APS). Mean t_PACH was 552 μm.

CONCLUSION

Biomicroscope asymmetry critically affects corneal thickness measurement in specular reflection. Induced errors can be accounted for and corrected, however. While the correction to the curvature radius is clinically relevant, it plays a minor role compared to asymmetry.

Corneal remodeling and spatial profiles following small incision lenticule extraction

PURPOSE

To evaluate the three-dimensional corneal spatial profiles following small incision lenticule extraction (SMILE) based on corneal asphericity, thickness, and volume.

MATERIALS AND METHODS

Eighty-three eyes in 83 patients who underwent SMILE were examined before and 1 and 6 months after surgery. The asphericity of the anterior and posterior corneal surfaces was analyzed. Corneal volume (CV) was measured in corneal regions measuring 3.0 mm, 5.0 mm, and 7.0 mm in diameter. Mean corneal thickness (CT) values were acquired at the apex (0.0 mm) and in four concentric radial zones from the apex (with diameters of 2.0, 4.0, 6.0, and 8.0 mm).

RESULTS

The mean anterior Q value increased from - 0.32 preoperatively to 0.67 at 1 month and 0.62 at 6 months postoperatively. The mean posterior Q value decreased from - 0.30 preoperatively to - 0.26 at 1 month and to - 0.25 at 6 months postoperatively. The CV increased by 0.05 ± 0.06 mm³ (1.40%), 0.06 ± 0.11 mm³ (0.83%), and 0.09 ± 0.17 mm³ (0.73%) along the radial zones with respective diameters of 3.0 mm, 5.0 mm, and 7.0 mm. The CT increased by 6.02 ± 6.48 µm (1.36%) at the apex and then decreased with increasing distance from the center, i.e., to 5.52 ± 6.31 µm (1.20%) at 2.0 mm, 4.72 ± 6.55 µm (0.92%) at 4.0 mm, 4.47 ± 7.86 µm (0.75%) at 6.0 mm, and 4.86 ± 10.31 µm (0.70%) at 8.0 mm. No correlations were observed between changes in CV and CT and refractive fluctuation between 1 month and 6 months postoperatively.

CONCLUSIONS

The corneal profile displayed a less oblate shift on the anterior surface; however, the posterior surface showed a slight backward shift during the postoperative period. The CV and CT steadily increased after surgery and mainly within the operative zones. Refraction remained stable postoperatively and was not affected by the corneal remodeling.

Measurement of anterior segment parameters in Saudi adults with myopia

Purpose

To measure anterior segment parameters of the eye in myopic Saudi population using Pentacam.

Method

This is retrospective cross-sectional study. Subjects were divided into three groups: low, moderate and high myopia groups. Anterior segment parameters including: central corneal thickness (CCT), thinnest corneal thickness (TCT), apex corneal thickness (Apex CT), corneal volume (CV), anterior chamber depth (ACD), anterior chamber volume (ACV) and corneal astigmatism (CA) were measured by Pentacam.

Results

A total of 504 eyes of 252 Saudi subjects with myopia were included in this study. The mean age ± standard deviation (SD) of subjects was 28.73 ± 6.18 years. The mean CCT, TCT, Apex CT, CV, ACD, ACV and CA for all myopic subjects were 557.21 ± 29.36, 554.09 ± 29.28, 556.10 ± 37.06, 61.30 ± 3.23 μm, 3.31 ± 0.27 mm, 211.15 ± 34.22 mm³ and 0.89 ± 0.52 D, respectively. No significant differences (P > 0.05) were found between right and left eyes in all anterior segment parameters of all myopic eyes. However, a significant difference (P < 0.05) was found in ACD between low (3.27 ± 0.26 mm) and moderate (3.35 ± 0.30 mm) myopic groups. Within low myopia group, significant differences (P < 0.05) were found in ACD, ACV and CA between different genders. Anterior chamber depth and ACV values were lower in females while CA was lower in males. In addition, significant positive correlation was found between ACV and ACD in all myopic groups.

Conclusion

This study provided valuable measurements of the anterior segments parameters of the eye in myopic Saudi population. These parameters could be useful for ophthalmic practitioners in the clinic.

Posterior cornea and thickness changes after scleral lens wear in keratoconus patients

PURPOSE

To evaluate the changes in the corneal thickness, anterior chamber depth and posterior corneal curvature and aberrations after scleral lens wear in keratoconus patients with and without intrastromal corneal ring segments (ICRS).

METHODS

Twenty-six keratoconus subjects (36.95 ± 8.95 years) were evaluated after 8 h of scleral lens wear. The subjects were divided into two groups: those with ICRS (ICRS group) and without ICRS (KC group). The study variables evaluated before and immediately after scleral lens wear included corneal thickness evaluated in different quadrants, posterior corneal curvature at 2, 4, 6 and 8 mm of corneal diameter, posterior corneal aberrations for 4, 6 and 8 mm of pupil size and anterior chamber depth.

RESULTS

There was a statistically significant corneal thinning (p < 0.05) in the inferior region of the KC group and in the superior region of the ICRS group. No change (p > 0.05) in the anterior chamber depth was found. The KC group showed a steepening (p < 0.05) in the temporal quadrant and a flattening that mainly affected to the superior-nasal quadrant. The ICRS group showed a steepening (p < 0.05) that mainly affected to the superior-nasal quadrant. Regarding posterior corneal aberrations, only changes (p < 0.05) in Z4 for 8 mm and Z8 for 4 mm were found in the KC group.

CONCLUSIONS

Short-term scleral lens wear showed a thinning of the cornea and changes in the posterior corneal curvature affects different regions in keratoconus patients with and without ICRS.

Changes in corneal thickness and corneal endothelial cell density after phacoemulsification cataract surgery: a double-blind randomized trial

Background

Age-related cataract is a leading cause of visual impairment, considered a global health burden, it is responsible for over 47% of blindness worldwide. Surgical intervention is usually the treatment of choice and phacoemulsification cataract surgery with implantation of an intraocular lens is the most common procedure, which may have several complications.

Objectives

To determine the effects of phacoemulsification surgery on corneal endothelial cell density and corneal thickness in patients undergoing cataract surgery.

Methods

The present study was conducted on patients diagnosed with immature senile cataract requiring surgical intervention from November 2013 to 2014 in Khatam al Anbia Hospital (a tertiary ophthalmology center). Physical examination included best-corrected visual acuity using the Snellen chart, refraction, slit-lamp bio-microscopy for anterior chamber evaluation, keratometry, Goldman tonometry, gonioscopy, and dilated indirect ophthalmoscopy, pachymetry, specular microscopy and biometry. Surgery was performed by similar method and technique in all patients. The change in the corneal endothelial cell count or density and central corneal thickness (CCT) number were compared preoperatively and one day, one week, one month, and three months post–operatively.

Results

A total of 92 eyes of 85 patients (43 females and 42 males with mean age of 62.1±12.2 years) were studied. Patients’ visual acuity improved (log MAR: 1±0.5 preoperatively to 0.45±0.34 post-operatively) (p=0.001). There was 11.4% endothelial cell loss (ECL) and significant decrease in ECC (from 2,791.15±99.86 to 2,472.87±472.14) (p=0.04). The central corneal thickness increased significantly (from 530.47±2.60 to 540.91±36.07). Diabetic patients (12.9%) had a statistically significant higher ECL rate after phacoemulsification (14.6% versus 8.7% respectively, p=0.002).

Conclusion

Phacoemulsification resulted in significant corneal endothelial damage, which is particularly important in patients with a borderline reservoir of endothelial cell, such as diabetic patients, which highlights the necessity of refining the current surgical methods and instruments to minimize the endothelial damage.

Trial registration

The trial was registered in the Thai clinical trial registry (http://www.clinicaltrials.in.th) with the ID: TCTR20171122001.

Funding

The study was supported by a research grant of Mashhad University of Medical Sciences.

Reproducibility of the measurement of central corneal thickness in healthy subjects obtained with the optical low coherence reflectometry pachymeter and comparison with the ultrasonic pachymetry

Background

Corneal pachymetry is widely used for refractive surgery and follow up in keratoconus, accurate measurement is essential for a safe surgery.

Objective

To assess intraobserver reliability of central corneal thickness (CCT) measurements using optical low-coherence reflectometry (OLCR) technology and its agreement with ultrasonic pachymeter (US).

Method

Randomized and prospective comparative evaluation of diagnostic technology. One randomly healthy eye of subjects was scanned three times with both devices. Intraobserver within-subject standard deviation (Sw), coefficient of variation (CVw) and intraclass correlation coefficient (ICC) were obtained for reliability analysis; for study agreement, data were analyzed using the paired-sample t test and the Bland-Altman LoA method. The mean of three scans of each equipment was used to assess the LoA.

Results

The study enrolled 30 eyes of 30 subjects with average age of 28.70 ± 8.06 years. For repeatability, the Sw were 3.41 and 5.96 µ, the intraobserver CVw was 2 and 4% and ICC 0.991 and 0.988, for OLCR and US respectively. The mean CCT difference between OLCR and US was 8.90 ± 9.03 µ (95% confidence interval: 5.52-2.27 µ), and the LoA was 35.40 µ.

Conclusions

OLCR technology provided reliable intraobserver CCT measurements. Both pachymetry measurements may be used interchangeably with minimum calibration adjustment.

Trans-epithelial corneal collagen cross-linking with iontophoresis for progressive keratoconus

PURPOSE

To evaluate the efficacy of trans-epithelial corneal collagen cross-linking (CXL) with Iontophoresis among patients with progressive keratoconus.

METHODS

It is a prospective interventional study, which is based on 41 eyes of 23 patients, suffering from progressive keratoconus and treated with trans-epithelial corneal cross-linking, using iontophoresis with ETDA and trometamol-enriched riboflavin 5 phosphates 0.1% hypotonic solution (Ricrolin+, Soot Italia SpA, Italy).

RESULTS

The mean of uncorrected distance visual acuity and best corrected distant visual acuity was improved at 6 months with statistically significant differences from baseline (p < 0.05). There was no statistically significant difference in keratometric values, including K₁, K₂, K_m, topographic astigmatism, and central corneal thickness. Patients, who had completed 1 year (21 eyes of 12 patients) of the treatment, showed similar results.

CONCLUSION

The data indicated that corneal collagens cross-linking with iontophoresis using Ricroli+ may be an effective method in halting the progression of keratoconus without the side effects of epithelial removal, which may be encountered in the standard epi-off CXL procedure.

Efficacy and safety of transepithelial corneal collagen crosslinking surgery versus standard corneal collagen crosslinking surgery for keratoconus: a meta-analysis of randomized controlled trials

Background

The aim of this study was to evaluate the efficacy and safety of transepithelial corneal collagen crosslinking (transepithelial CXL) versus standard corneal collagen crosslinking (epithelium-off CXL) on keratoconus.

Methods

Eligible studies were identified by systematically searching PubMed, the Cochrane Library and Embase. Topographic parameters, corrected distant visual acuity (CDVA), uncorrected distant visual acuity (UDVA), and corneal thickness (CT) were assessed by the pooled weighted mean differences (WMDs) of the change from baseline to the end of follow up. Quality was assessed according to Cochrane handbook. And we used Review Manager to analysis the included trials.

Results

Three trials involving 244 eyes were evaluated, with 111 eyes in the standard CXL group and 133 eyes in the transepithelial CXL group. The pooled results showed that there were significant differences between the two groups in maximum keratometry (mean difference = 1.05D, 95% CI 0.19 to 1.92, P = 0.02)),and the standard CXL is more effective in decreasing the maximum keratometry at least 12 months after operation; the transepithelial CXL group gained more improvement in CDVA (mean difference = −0.07, 95% CI -0.12 to −0.02, P = 0.007);there were no significant differences in uncorrected distant visual acuity (UDVA) between the two groups (mean difference = −0.03, 95% CI -0.20 to 0.15, P = 0.75). A similar change was found in corneal thickness (mean difference = 4.35, 95% CI -0.43 to 9.13, P = 0.07)).

Conclusions

The standard CXL is more effective in decreasing the maximum keratometry than the transepithelial CXL; the transepithelial CXL provided favorable visual outcomes; they both exhibit similar safety.

Reproducibility of corneal, macular and retinal nerve fiber layer thickness measurements using the iVue-100 optical coherence tomography

Purpose

To determine the intra-session and inter-session reproducibility of corneal, macular and retinal nerve fiber layer thickness (RNFL) measurements with the iVue-100 optical coherence tomography in normal eyes.

Methods

These parameters were measured in the right eyes of 50 healthy participants with normal vision. Six scans each for corneal thickness, macular and optic nerve head were taken on one day (intra-session), followed by similar repeated measures on five separate days (inter-session). Reproducibility was computed using intra-class correlation coefficient (ICC), coefficient of variation (COV), and test-retest variability (TRV).

Results

For intra-session reproducibility, the ICC, COV and TRV values for mean corneal thickness were 0.924, 2.82%, and 3.06 µm respectively. For the mean macular thickness, they were 0.978, 4.64% and 4.51 µm respectively, while for mean RNFL thickness they were 0.946, 3.19%, and 5.66 µm respectively. Inter-session values for mean corneal thickness were 0.926, 2.65% and 3.48 µm, and 0.916, 2.24% and 2.03 µm for mean macular thickness. For mean RNFL thickness, they were 0.962, 2.21%, and 4.72 µm respectively.

Conclusion

There was good reproducibility of all measured parameters. However, mean RNFL thickness measurements were the most reproducible, suggesting that this may be the best parameter to use to determine measured changes over time.

Comparison of Central Corneal Thickness Measurements by Pentacam and Ultrasound Pachymetry in Normal Myopic Patients

Introduction

Precise measurement of corneal thickness is of crucial importance in corneal refractive procedures. The aim of this work is to compare the central corneal thickness measurements using Scheimpflug imaging (Pentacam) and contact US pachymetry in normal myopic patients.

Methods

This retrospective cohort study was conducted on in 144 eyes of 72 normal myopic patients during 6 months. The study location was the Research Institute of Ophthalmology (Giza, Egypt), and Magrabi Eye Hospital (Dubai, United Arab Emirates). Central corneal thickness was measured with the two devices. Data were analyzed by descriptive statistics, independent-samples t-test, paired-samples t-test, Mann-Whitney U test and Pearson-Product Moment Correlation Coefficient.

Results

The mean age was 25.3±5.6 years (range 18 to 38 years). The median age for our patients is 24 years. The average measurements of CCT were 526.8±35.3 and 529.1±37.9 for the Pentacam pachymetry and US pachymetry values, respectively. Mean difference between both measurements was 2.3±2.6μm which is statistically insignificant (p=0.08). Bland Altman Plot shows border line agreement of the two methods US pachymetry and Pentacam in detection of central corneal thickness.

Conclusion

The results of this study showed no significant differences in CCT readings between the measurements obtained by Pentacam and US pachymetry in normal myopic patients.

Corneal thickness differences between type 2 diabetes and non-diabetes subjects during preoperative laser surgery examination

AIMS

To evaluate the differences in corneal thickness between type 2 diabetes subjects with HbA1c under 7.0% and non-diabetes subjects during their preoperative laser surgery examinations.

METHODS

The mean of five consecutive corneal thickness measurements at the central and mid-peripheral cornea was obtained by means of noncontact scanning-slit corneal topography (Orbscan Topography System II; Orbscan, Inc., Salt Lake City, UT, USA) in 35 myopic non-insulin dependent type 2 diabetes subjects (17 males and 18 females) and 48 healthy myopic controls (23 males and 25 females).

RESULTS

The corneal thickness values at the central and mid-peripheral cornea were significantly higher in the diabetic group (p<.001). The diabetic subjects presented the highest thickness value in the superior cornea (n=22; 62.9%) followed by the nasal (n=9; 25.7%) and the temporal (n=4; 11.4%) cornea, but never in the inferior cornea. The control subjects presented the highest thickness value in the superior cornea (n=19; 39.6%) followed by the nasal (n=18; 37.5%), the inferior (n=6; 12.5%), and the temporal (n=3; 6.3%) cornea. The central corneal thickness (CCT) of the diabetes patients was not statistically correlated with their HbA1c (r²=.078; p=.104), body mass index (r²=.007; p=.633), and time from diagnosis of diabetes (r²=.025; p=.363), but it was correlated with their corneal endothelial cell density values (r²=.543; p<.001).

CONCLUSIONS

Diabetes subjects with HbA1c under 7.0% who are candidates for laser refractive surgery present thicker corneas than their age-matched control subjects. In these patients, there is a correlation between their CCT values and their corneal endothelial cell density values, so when higher CCT values were found, lower corneal endothelial cell density values were observed.

Corneal thickness measurements with Scheimpflug and slit scanning imaging techniques in keratoconus

PURPOSE

To determine the repeatability of corneal thickness measurements with Scheimpflug (Pentacam) and slit scanning (Orbscan) imaging techniques in different grades of keratoconus.

METHODS

This study was conducted as a cross-sectional research. Imaging with Orbscan and Pentacam was performed on patients with different grades of keratoconus. With each device, 3 measurements were taken at 10 min intervals. Repeatability indices in different grades of keratoconus were calculated for each device.

RESULTS

Seventy-four eyes of 42 keratoconus patients were enrolled. Repeatability index (RI) of central corneal thickness (CCT) measurements in keratoconus grade 1, 2, and 3, were 12.8, 9.9, and 24.2 with Pentacam, and 23.6, 26.3, and 59.3 with Orbscan, respectively. For the thinnest point, these figures were 9.6, 8.0, and 35.7 with Pentacam and 19.5, 16.6, and 26.8 with Orbscan, respectively. The 95% limit of agreement (LOA) between Pentacam and Orbscan in measuring CCT and thinnest point in grade 1 were -25.5-47.7 mic and -33.3-32.8 mic, respectively. These results for grade 2 were -9.8-50.6 mic and -26.2-43.7 mic, respectively. In grade 3, 95% LoA were -20-64.6 mic and -31.4-60.5 mic, respectively.

CONCLUSIONS

The results of this study showed that although repeated measurements of the CCT with Orbscan and Pentacam are strongly correlated, repeatability values of CCT measurements significantly decrease at more advanced grades of keratoconus. In all keratoconus grades, repeatability of CCT measurements was better with Pentacam than Orbscan. These findings indicate that corneal thickness readings have less validity in patients with advanced keratoconus.