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.

Assessing the efficacy of four methods established by four parameters in ICL size selection and relevant influencing factors: a prospective cohort study

PURPOSE

To compare the efficacy and relevant influencing factors of four ICL size selection methods established by four different parameters.

METHODS

This prospective study included 60 patients (120 eyes) who underwent bilateral ICL implantation. Patients were equally divided into four groups, and each group used the Parkhurst nomogram based on sulcus-to-sulcus (STS), the manufacturer's Online Calculation & Ordering System (OCOS) nomogram based on white-to-white (WTW), the KS formula based on angle-to-angle (ATA) and the NK formula based on anterior chamber width (ACW) to determine the ICL size. Recorded the vault one month after operation and compared the consistency between STS and WTW, ATA and ACW and their effects on the vault of different groups.

RESULTS

The Parkhurst nomogram, OCOS nomogram, KS formula and NK formula determined 86.7%, 70.0%, 83.3% and 66.7% of properly sized ICL, respectively. STS and ATA were correlated (P < 0.05). The mean difference between the STS and WTW, ATA and ACW was -0.37 ± 0.62 mm, -0.42 ± 0.53 mm and -0.44 ± 0.52 mm, respectively. The vault in the OCOS group was negatively correlated with △STS-WTW, and the vault in the NK group was negatively correlated with △STS-WTW, △STS-ATA and △STA-ACW. The vault in the Parkhurst group and KS group was not affected by anterior segment biometry variables.

CONCLUSION

ATA can be served as an alternative parameter to STS, and STS-based Parkhurst nomogram and ATA-based KS formula determined the most appropriate ICL size. When using OCOS nomogram and NK formula to select ICL size, postoperative abnormal vault was associated with a larger difference between STS and other anterior segment parameters.

Characterization of the external limbus on corneoscleral topography with ultrawide-field optical coherence tomography

PURPOSE

To present a new method for 3-dimensional external limbal demarcation on corneoscleral topography derived from optical coherence tomography (OCT). Limbal shape is investigated and compared to other landmarks.

METHODS

Images from the anterior segment were obtained with a ultrawide-field (20 mm) OCT. An automated algorithm was developed to demarcate the topographic limbus based on the transition from corneal to scleral curvature. The internal limbus was manually identified as the scleral spur on the OCT images. The external topographic limbus was fit with a circle on a plane. Ellipticity and ovality were defined by the lateral limbal deviation from the best-fit circle. Toricity was defined by the axial deviation from the best-fit plane. Repeatability was assessed by the within-subject standard deviation from two repeated measurements. For comparison, the white-to-white (WTW) diameter was obtained from Pentacam HR.

RESULTS

18 eyes from 11 subjects were analyzed. The topographic limbal diameter was 12.16 ± 0.68 mm (mean ± standard deviation) horizontally and 11.18 ± 0.65 mm vertically. The repeatability for the topographic limbal diameter was 0.054 mm. The internal and WTW horizontal limbal diameters were significantly smaller (linear mixed-effects model (GLMM), p <.017). The vertical internal limbal diameter was significantly larger (GLMM p <.05). The topographic limbus had significant ellipticity (0.25 ± 0.13 mm, wider horizontally, repeatability of 0.07 mm) and toricity (0.15 ± 0.08 mm, flatter horizontally, repeatability of 0.10 mm). Low coefficients of determination were found for the topographical limbus with the internal limbus (R2=0.021 and R2=0.039, for horizontal and vertical diameters respectively) and with the WTW (R2=0.146 for the horizontal diameter).

CONCLUSION

The proposed method to demarcate the 3D external topographical limbus is repeatable. The topographic limbal shape and size cannot be accurately derived from WTW nor internal limbus measures. This new technology may improve the process of scleral lens fitting.

Agreement of anterior segment measurements between LenStar LS 900 optical biometer and OPD Scan III wavefront aberrometer devices in eyes with cataract

PURPOSE

To compare the inter-device agreement of anterior eye segment measurements between LenStar LS 900 optical biometer and OPD Scan III wavefront aberrometer.

METHODS

This is a retrospective study involving 59 patients (78 eyes) with cataract. Their angle Alpha, angle Kappa, pupil size and white-to-white (WTW) distance were measured by LenStar LS 900 optical biometer and OPD Scan III wavefront aberrometer, respectively, and pairwise agreement comparisons were performed between them.

RESULTS

The most agreement of various parameters was occurred, with intraclass correlation coefficient (ICC) of WTW = 0.930; angle Alpha = 0.853; angle Kappa = 0.898; and pupil size = 0,976 in bright environment. Furthermore, in dark environment, the ICC of WTW, angle Alpha, angle Kappa, and pupil size were 0.927, 0.791, 0.915, and 0.990, respectively. Bland-Altman plot showed similar excellent agreement in the outcomes of the two devices for these measurements testing.

CONCLUSIONS

There was an excellent agreement between the LenStar LS 900 optical biometer and OPD Scan III wavefront aberrometer for WTW, angle Alpha, angle Kappa, and pupil size measurements. In clinical practice, these measurements obtained by LenStar LS 900 optical biometer and OPD Scan III wavefront aberrometer can be used interchangeably.

Lens-vault analysis and its correlation with other biometric parameters using swept-source OCT

PURPOSE

To measure lens vault (LV) and to assess its correlation with various ocular parameters in healthy eyes, using for all measurements the same high-resolution swept-source optical coherence tomographer (SS-OCT).

METHODS

We prospectively recruited 67 Caucasian healthy patients whose mean age was 41.9 ± 12.4 years; only their right eye was included in the study. Data were all recorded with the ANTERION SS-OCT and comprised, for each patient, 5 consecutive measurements of LV, anterior chamber depth (ACD), lens thickness (LT), axial length (AL), white-to-white (WTW) distance, central corneal thickness (CCT), anterior chamber volume (ACV) and spur-to-spur (STS) distance.

RESULTS

Mean LV was 0.26 ± 0.23 mm (ranging from -0.24 to 0.78 mm). Data analysis revealed a statistically significant negative correlation between LV and ACD (R=-0.80, p < 0.001), AL (R = -0.36, p = 0.002), and ACV (R = -0.68, p < 0.001), and a positive correlation between LV and LT (R = 0.67, p < 0.001), and age (R = 0.53, p < 0.001). In contrast, no statistically significant correlation was found between LV and WTW (R=-0.17, p = 0.15), CCT (R = 0.11, p = 0.36) or STS (R=-0.10, p = 0.41).

CONCLUSIONS

Taking into account our findings about intra-parameter correlation levels, we believe that LV should be measured and analyzed together with other ocular parameters in clinical routine practice both for diagnosis and for some refractive surgeries.

Effect of the Difference Between the White-to-White and Sulcus-to-Sulcus on Vault and the Related Factors After ICL Implantation

INTRODUCTION

To assess the differences between the horizontal white-to-white (WTW) and horizontal sulcus-to-sulcus (STS) diameter measurements, their related factors, and their effects on vault after implantable Collamer lens (ICL) implantation.

METHODS

This retrospective study included 429 eyes of 429 patients (145 men and 284 women with a mean age of 29.22 ± 8.06 years) who underwent ICL implantation. The choice of the ICL size depended on the WTW diameter and anterior chamber depth (ACD). The information of WTW diameter, STS diameters, ACD, and their relationships on vault were analyzed.

RESULTS

Horizontal STS and WTW diameters were correlated (r = 0.71, P < 0.001). The mean difference between the STS and WTW diameters was -0.02 ± 0.33 (-1.36 to 1.11) mm. The average vaults of the ^△STS-WTW < -0.1 group, - 0.1 ≤ ^△STS-WTW ≤ 0.1 group, and ^△STS-WTW > 0.1 group were 558.36 ± 163.58 (250-1100) μm, 513.10 ± 121.42 (190-850) μm, and 469.01 ± 133.23 (120-750) μm, respectively. There were significant differences between these groups (P < 0.05). ^△STS-WTW was correlated with the horizontal STS diameter (r = 0.30, P < 0.001), the WTW diameter (r = -0.17, P = 0.001), and the ACD (r = 0.17, P < 0.001). When the WTW diameter was further away from 11.08 to 12.51 mm or the ACD was further away from 2.81 to 3.74 mm, the difference between the STS and WTW diameters was larger and the correlation between the STS and WTW diameters was weaker.

CONCLUSIONS

The difference between the WTW and STS diameters was larger for cases with a WTW diameter or anterior chamber depth outside a certain range; this may be associated with an undesirable vault after ICL implantation. Special attention should be paid to these patients.

Agreement of white-to-white measurements with swept-source OCT, Scheimpflug and color LED devices

PURPOSE

To assess the interchangeability of different devices for measuring white-to-white (WTW) distance.

METHODS

WTW distance was measured in 53 eyes of 53 patients using Anterion swept-source optical coherence topographer (SS-OCT), IOLMaster 700 SS-OCT, Pentacam HR Scheimpflug and Cassini color LED. Statistical analysis was done by means of the Friedman test and the post hoc Tukey test. The Bland-Altman analysis was applied to carry out pairwise comparisons with the average difference, 95% confidence interval of the average difference and limits of agreement 95% (LoA).

RESULTS

WTW values obtained by the Anterion, IOLMaster 700, Pentacam HR and Cassini were: 11.84 ± 0.41 mm, 11.96 ± 0.41 mm, 11.68 ± 0.38 mm and 12.65 ± 0.52 mm, respectively. Statistically significant differences were found in all pairwise comparison (p < 0.001). The lowest mean difference was found between the Anterion and IOLMaster 700 (- 0.11 mm) and the highest between the Pentacam HR and Cassini (- 0.96 mm). The widest LoA ranges were those that compared any device with the Cassini. LoA ranges when the other three devices were compared among them were similar: Anterion versus IOLMaster 700, Anterion versus Pentacam HR and IOLMaster versus Pentacam HR (about 0.2 mm).

CONCLUSIONS

Our results show that there were statistically significant differences in WTW measurement among the four devices, but under a clinical point of view, we believe that Anterion and IOLMaster 700 may be considered interchangeable and so Anterion and Pentacam HR, however, IOLMaster 700 and Pentacam HR may not and neither is Cassini with any of the other three devices.

Angle-to-angle and spur-to-spur distance analysis with high-resolution optical coherence tomography

Background

To measure angle-to-angle (ATA) and spur-to-spur (STS) distances along six meridians using high-resolution swept-source optical coherence tomography (SS-OCT) and to compare those values with horizontal white-to-white (WTW) distance.

Methods

68 eyes from 68 patients were quantitatively assessed with the Anterion SS-OCT (Heidelberg Engineering, Heidelberg, Germany). ATA and STS distances were measured with the SS-OCT’s B-Scan in six cross-sectional images corresponding to the vertical (6–12 o’clock), 1–7 o’clock, 2–8 o’clock, horizontal (3–9 o’clock), 4–10 o’clock and 5–11 o’clock meridians. WTW was measured horizontally with the device’s infrared camera. A Pearson correlation analysis was carried out to compare ATA and STS distances with WTW.

Results

The largest values were found for the vertical meridian and the shortest for the 2–8 o’clock meridian, both for ATA and STS distances. No statistically significant differences were found between WTW, ATA and STS along the horizontal meridian (p > 0.1). However, ATA and STS showed statistically significant differences elsewhere, except for the horizontal and the 2–8 o’clock meridians (p > 0.05). Moreover, we found that ATA and STS varied significantly depending on the meridian being assessed, except for ATA at 4–10 versus 3–9 o’clock and for STS at 4–10 versus 3–9 o’clock and at 3–9 versus 2–8 o’clock (p > 0.1). R² values ranged from 0.49 to 0.75 for ATA and STS at the different meridians, showing the best correlation at 3–9 o’clock meridian (0.64 and 0.75, respectively) and the worst at 6–12 o’clock meridian (R² = 0.49 for both ATA and STS).

Conclusions

ATA and STS distances vary radially, thus showing that the anterior chamber is vertically oval. Therefore, it is advisable to measure these two distances along the meridian to be used.

Influence of pupil dilation on the Barrett universal II (new generation), Haigis (4th generation), and SRK/T (3rd generation) intraocular lens calculation formulas: a retrospective study

BACKGROUND

Despite the surge in the number of cataract surgeries, there is limited information available regarding the influence of pupil dilation on predicted postoperative refraction and its comparison with recommended various intraocular lens power calculated using the different parameters. We used three different IOL power calculation formulas: Barrett Universal II (Barrett) (5-variable formula), Haigis (3-variable formula), and SRK/T (2-variable formula), in order to investigate the potential effect of pupil dilation on the predicted postoperative refraction (PPR) and recommended intraocular lens (IOL) power calculation.

METHODS

This retrospective study included 150 eyes. All variables were measured and calculated using a ZEISS IOL Master 700. The following variables were measured before and after dilation: anterior chamber depth (ACD), lens thickness (LT), white-to-white (WTW). PPR and recommended IOL power were calculated by Barrett, Haigis, and SRK/T IOL calculation formulas. The change in each variable before and after dilation, and the correlations between all changes were analyzed using the Wilcoxon signed-rank test and the Spearman's rank-order correlation test, respectively.

RESULTS

The mean absolute change (MAC) in PPR before and after dilation was found to be highest in the Barrett formula. Significant differences were found between each MAC (P <  0.0001). Significant changes were observed before and after dilation in ACD and LT (P <  0.0001), but not in WTW. Using the Barrett and Haigis formulas, there was a significant positive correlation between the change in PPR and change in ACD (P <  0.0001), and a negative correlation between change in PPR and change in LT (P <  0.0001). The correlations were strongest with the Barret formula followed by the Haigis, particularly in terms of LT. Changes in PPR determined by the Barrett formula also demonstrated a significant positive correlation with changes in WTW (P = 0.022). The recommended IOL power determined using Barrett and Haigis changed before and after dilation in 23.3 and 19.3% cases respectively, while SRK/T showed no change.

CONCLUSIONS

In terms of PPR and recommended IOL power, pupil dilation influenced mostly the Barrett formula. Given the stronger correlation between the changes in PPR when using Barrett and the changes in ACD, LT, and WTW, changes in ACD, LT, and WTW significantly affect how dilation influences the Barrett formula. Determining how dilation influences each formula and other variables is key to improving the accuracy of IOL calculations.

Decentration of a toric intraocular lens implant in a patient with simple megalocornea

Purpose

To describe a patient who developed radial displacement of the capsular bag and toric intraocular lens implant within approximately 5 weeks after surgery.

Observations

A patient underwent uncomplicated cataract extraction and implantation of a toric IOL for 2.5 diopters (D) of preoperative corneal astigmatism. Uncorrected visual acuity (UCVA) on postoperative day 1 was 20/20. Blurriness developed 5 weeks after surgery when UCVA was 20/70 but corrected to 20/20 with 2 D of cylinder in a new axis. The IOL was in the proper axis, but it and the capsular bag were radially displaced. Dilated examination revealed posterior capsular opacification superotemporally, outside the visual axis. The patient's biometry revealed axial myopia and megalocornea (white-to-white measurement of 13.44 mm), suggesting a larger than average capsular bag. Surgery was performed at postoperative week 6 to expand the capsular bag using a capsular tension ring and to re-center the IOL keeping the same axis. The patient recovered UCVA of 20/25 after the IOL was recentered.

Conclusions and Importance

It is important to review biometry for large white-to-white measurements. Eyes with megalocornea may require capsular tension rings at time of toric IOL implantation so as to maintain IOL centration and good UCVA.

Intrasession repeatability of ocular anatomical measurements obtained with a multidiagnostic device in healthy eyes

Background

To evaluate the intrasession repeatability of anterior chamber depth (ACD), central (CCT) and peripheral corneal thickness (PCT), white-to-white diameter (WTW), and irido-corneal angle (IA) measurements obtained with a multidiagnostic device in healthy eyes.

Methods

A total of 107 eyes of 107 patients ranging in age from 23 to 65 years were examined with the VX120 system (Visionix-Luneau Technologies). Three consecutive measurements were obtained with this device to assess the intrasession repeatability of ACD, CCT, PCT at different nasal and temporal locations, WTW, and nasal and temporal IA. Data analysis included the calculation of within-subject standard deviation (S_w), intrasubject precision (1.96xS_w), coefficient of variation (CV) and intraclass correlation coefficient (ICC).

Results

The S_w and CV for ACD was 0.03 mm and 1.16%, respectively, with an ICC of 0.992. The S_w values for central and peripheral pachymetric measurements were below 9 μm, with CV of less than 1.6% and ICC of 0.976 or higher. For IA measurements, S_w values of 0.84 or lower were found, with a CV between 1 and 2%, and an ICC of more than 0.970. The S_w for WTW was 0.24 mm and the CV was 1.95%. No statistically significant correlations were found between any anatomical parameter evaluated and their S_w and CV values associated (−0.220 ≤ r ≤ 0.204, p ≥ 0.125).

Conclusions

The VX120 system is able to provide repeatable measurements of anatomical parameters in healthy eyes. Inter-observer repeatability should be evaluated in future studies.

Comparison of keratometry and white-to-white measurements obtained by Lenstar with those obtained by autokeratometry and corneal topography

PURPOSE

To compare anterior eye segment measurements obtained using low optical coherence reflectometry (LENSTAR LS900, Haag-Streit), autokeratometry (RC-5000, Tomey) and corneal topography (Topolyzer, Wavelight).

METHODS

In 46 healthy subjects, flat keratometry (Kf), steep keratometry (Ks), mean keratometry (Km) and white-to-white (WTW) distance were measured by Lenstar, Tomey RC-5000 and Topolyzer.

RESULTS

Kf and Km measurements of Lenstar were significantly steeper than Tomey RC-5000 (both p<0.001), but the 95% LoA of them were narrow (-0.22 to 0.46D, -0.16 to 0.36D, respectively). There were no significant differences between the Kf and Km measurements of Lenstar and Topolyzer, with a narrow 95% LoA. There were no significant differences between the Ks measurements of Lenstar and Tomey RC-5000, and Lenstar and Topolyzer. A good agreement was found between them with 95% LoA of -0.40 to 0.56D, and -0.56 to 0.64D, respectively. WTW measurements with Lenstar were greater than those with Tomey RC-5000 and Topolyzer (p=0.042, p<0.01, respectively). A good agreement existed between the WTW obtained by Lenstar and Topolyzer, Tomey RC-5000, with 95% LoA ranging from -0.13 to 0.74mm and -0.33 to 0.51mm.

CONCLUSIONS

Generally good agreement was found between the Lenstar and Tomey RC-5000, Topolyzer for K and WTW measurements. In clinical practice, K and WTW measurements obtained by Lenstar and Tomey RC-5000, Topolyzer can be used interchangeably.