Evaluation of Corneal Epithelial Thickness Imaged by High Definition Optical Coherence Tomography in Healthy Eyes

Analysis of central corneal thickness in systemic lupus erythematosus

Introduction

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease with ocular involvement in up to 30% of cases. Due to its type I collagen composition, the cornea is particularly susceptible to thinning due to immune-complex deposition. A reduced central corneal thickness (CCT) is clinically relevant in glaucoma, where a thinner CCT increases glaucoma risk and in refractive surgery planning. Previous studies on CCT in SLE are limited due to methodological heterogeneity, technology use, inclusion criteria, and sample size, resulting in conflicting findings. This study aims to evaluate and compare the mean CCT values between patients with SLE and healthy controls.

Materials and methods

This cross-sectional study assessed mean CCT in 71 participants, 36 patients with SLE and 35 age- and sex-matched healthy controls, recruited from ophthalmology consultations. Participants with other risk factors for corneal thinning were excluded. A pilot study estimated a sample size of 34 participants per group. After confirming concordance using the Kappa index, one randomly selected eye per participant was included. CCT was measured using Zeiss HD Cirrus 5,000 optical coherence tomography. Correlation analysis was conducted using Spearman's Rho coefficient, while a Loess regression was performed to visualize both linear and non-linear trends. Multivariate linear regression assessed the relationship between CCT, SLE, and other variables.

Results

Patients in the SLE group exhibited significantly thicker CCT than controls (536.44 ± 39.91 μm vs. 517.57 ± 29.62 μm, p = 0.014). Intraocular pressure (IOP) was similar between groups (14.31 ± 3.12 mmHg vs. 14.54 ± 2.36 mmHg, p = 0.898). CCT positively correlated with the length of hydroxychloroquine (HCQ) use (R: 0.357; p = 0.041), showing a trend toward an increase with prolonged usage, peaking approximately 100 months. Multivariate regression confirmed the association between SLE and higher CCT, potentially due to HCQ use.

Discussion

We established an association between CCT and the presence of SLE, with SLE patients exhibiting significantly higher CCT values, potentially due to hydroxychloroquine use. These findings have important implications for IOP assessment, glaucoma risk evaluation, and refractive surgery planning in SLE patients and those undergoing treatment with HCQ. Further prospective studies are warranted to validate these observations and explore the underlying mechanisms.

Corneal Epithelial Thickness Mapping in Healthy Population Corneas Using MS-39 Anterior Segment Optical Coherence Tomography

Purpose

The corneal epithelium is the outermost layer of the cornea. It plays a vital role in both normal and pathological conditions of the eye surface and serves as a protective layer. This study aimed to evaluate corneal epithelial thickness (ET) and create a normative database of corneal ET for pediatric and adult age groups using MS-39 AS-OCT.

Patients and Methods

This is a cross-sectional multi-center study conducted among the Saudi population.

Results

A total of 268 eyes of 268 patients were analyzed (male 50.7% vs female 49.3%). 53.8% were pediatric age group. Higher mean values of central, paracentral, and peripheral were associated with the adult age group except for superior paracentral, temporal peripheral, and nasal peripheral. Male patients had higher mean values of central, paracentral, and peripheral in each quadrant, except for inferior peripheral. There was a significant correlation between inferior, superior, nasal, and temporal in both paracentral and peripheral. No significant correlations were observed between the spherical equivalent and epithelial thickness map.

Conclusion

The study found sex differences, with females generally having lower ET values than males, and older age having higher values than children.

The role of corneal epithelial thickness map in detecting early keratoconus

PURPOSE

To detect subtle changes in early keratoconus by evaluating corneal epithelial thickness differences among patients with binocular very asymmetric ectasia (VAE) and normal subjects.

METHODS

Corneal epithelial thickness was measured using the Fourier-domain AS-OCT system RTVue® 100 (Optovue, Fremont, CA, USA). 152 eyes from 76 patients were divided into three groups: Very asymmetry ectasia-ectasia (VAE-E, n = 38), Very asymmetry ectasia-normal topography (VAE-NT, n = 38), and Normal control (NC, n = 76). Discrimination capacity was assessed using areas under the curve (AUC) of receiver operator characteristic (ROC) curves.

RESULTS

In the keratoconus group, the epithelial Min (minimum), central, midperipheral I (inferior), midperipheral IT (inferior-temporal), peripheral IT, and midperipheral T (temporal) were thinner (all P < 0.05). The topography normal group had thinner midperipheral IN (inferior-nasal), peripheral IN, midperipheral T, and peripheral T, and larger Max-Min and Std. Dev (P < 0.05). For diagnosing typical keratoconus, Std. Dev (AUC = 0.982, sensitivity 97.4%, specificity 92.1%) had the highest diagnostic efficiency. Combining four variables (Minimum, Max-Min, Midperipheral IT, and Midperipheral I) performed well in distinguishing topography normal eyes (AUC = 0.896, sensitivity 76.3%, specificity 89.5%). Multivariable analysis using epithelial parameters combined with Pentacam random forest index (PRFI) yielded the best results (AUC = 0.951, sensitivity 90.6%, specificity 89.5%).

CONCLUSIONS

The corneal epithelial parameters play an important auxiliary role in the diagnosis of keratoconus and the screening of subclinical keratoconus. Combination of epithelial parameters and tomographic parameters can improve the sensitivity of early stage keratoconus detection.

Assessment of corneal epithelial thickness mapping by spectral-domain optical coherence tomography

Background

To assess corneal epithelial-thickness (ET) mapping resulting from spectral-domain-optical-coherence-tomography (SD-OCT) by analysing its repeatability and reproducibility and its utility for screening corneal-refractive-surgery (CRS) candidates.

Methods

ET was measured in 25-sectors by two-operators. Intra-subject-standard-deviation, coefficient-of-repeatability (CoR) and coefficient-of-variability (CoV) were calculated to evaluate repeatability. Reproducibility was evaluated using a Bland-Altman analysis. Scheimpflug-tomography, refraction, visual acuity, and patient history were used to make a decision on eligibility for CRS. After this decision, the surgeon was shown the patient's ET map and was asked to reconsider his analysis. The percentage of screenings that changed after evaluating the ET maps was determined.

Results

Forty-three eyes with normal corneas (CRS-group) and 21 eyes not suitable for CRS (non-CRS-group) were studied. For the CRS-group, CoR ranged from 2.03 (central) to 19.73 μm (outer-inferonasal), with the central-sector showing the highest repeatability (CoV: 1.53-1.80%). For the non-CRS-group, CoR ranged from 3.82 (central-middle-superonasal) to 13.42 μm (middle-inferotemporal), with the inner-superonasal-sector showing the highest repeatability (CoV: 2.86-4.46%). There was no statistically significant difference between operators (p > 0.01). In the CRS-group, the outcomes showed a narrow 95% limits-of-agreement (LoA) for the central-and inner-nasal-sectors (about 4 μm), and wider for the inner-superior, outer-superotemporal and outer-inferonasal (about 10-14 μm). In the non-CRS-group, they were for the outer superonasal (about 4 μm), and for the middle-inferotemporal and outer-temporal (about 10 μm), respectively. Candidacy for CRS changed in 7.82% of patients after evaluation of the ET maps, with all of them screened-out.

Conclusion

The SD-OCT provided repeatable and reproducible corneal ET measurements and may alter candidacy for CRS.

Clinical trial registration

German Clinical Trials Register: https://drks.de/search/en/trial/DRKS00032797, identifier: DRKS00032797.

Corneal Epithelial Thickness Mapping: A Major Review

The corneal epithelium (CE) is the outermost layer of the cornea with constant turnover, relative stability, remarkable plasticity, and compensatory properties to mask alterations in the underlying stroma. The advent of quantitative imaging modalities capable of producing epithelial thickness mapping (ETM) has made it possible to characterize better the different patterns of epithelial remodeling. In this comprehensive synthesis, we reviewed all available data on ETM with different methods, including very high-frequency ultrasound (VHF-US) and spectral-domain optical coherence tomography (SD-OCT) in normal individuals, corneal or systemic diseases, and corneal surgical scenarios. We excluded OCT studies that manually measured the corneal epithelial thickness (CET) (e.g., by digital calipers) or the CE (e.g., by confocal scanning or handheld pachymeters). A comparison of different CET measuring technologies and devices capable of producing thickness maps is provided. Normative data on CET and the possible effects of gender, aging, diurnal changes, refraction, and intraocular pressure are discussed. We also reviewed ETM data in several corneal disorders, including keratoconus, corneal dystrophies, recurrent epithelial erosion, herpes keratitis, keratoplasty, bullous keratopathy, carcinoma in situ, pterygium, and limbal stem cell deficiency. The available data on the potential role of ETM in indicating refractive surgeries, planning the procedure, and assessing postoperative changes are reviewed. Alterations in ETM in systemic and ocular conditions such as eyelid abnormalities and dry eye disease and the effects of contact lenses, topical medications, and cataract surgery on the ETM profile are discussed.

Impact of Corneal Toricity on the Distribution of Corneal Epithelial Thickness

PURPOSE

To investigate the impact of corneal toricity on the distribution characteristics of corneal epithelial thickness (CET).

METHODS

A total of 330 eyes in 330 healthy participants were included in this study. They were divided into two groups based on the median of the corneal toricity value: low-toricity group (corneal toricity < 1.50 diopters) and high-toricity group (corneal toricity ≥ 1.50 diopters). The CET within a 9-mm-diameter area of the central cornea was obtained using optical coherence tomography. The difference of CET value between flat and steep meridians (F-S CET) was defined to evaluate the CET distribution. The F-S CET between the two groups was compared, and the correlations between F-S CET and the corneal toricity were analyzed.

RESULTS

The CET was thinner in the superior-peripheral area than in other areas. A slight intergroup difference was noted in terms of the F-S CET at the paracentral (0.11 ± 0.93 vs 0.32 ± 0.92, P = .038), midperipheral (0.45 ± 0.78 vs 0.77 ± 0.89, P = .001), and peripheral (3.11 ± 2.18 vs 4.10 ± 2.38, P < .001) zone. In each zone, the difference in F-S CET between the two groups was less than 1 μm. As the area expanded, the F-S CET continued to increase (F = 850.303, P < .001). A weak correlation was observed between F-S CET and corneal toricity (r = 0.103 to 0.240); however, this correlation was not significant in the paracentral zone. Covariance analysis demonstrated that F-S CET was slightly correlated with age, refractive state, and intraocular pressure.

CONCLUSIONS

The corneal toricity did not significantly affect the distribution of the corneal epithelium in normal corneas. [J Refract Surg. 2023;39(7):482-490.].

Systematic detection of keratoconus in OCT: corneal and epithelial thickness maps

PURPOSE

To detect keratoconus (KC) only by analyzing the corneal and epithelial map parameters and patterns in optical coherence tomography (OCT).

SETTING

Tertiary care refractive surgery center.

DESIGN

Retrospective data collection.

METHODS

Corneal and epithelial thickness maps of normal, manifest, and subclinical keratoconic eyes (according to the Belin-Ambrosio display, Pentacam) were evaluated using spectral-domain OCT (Zeiss Cirrus 5000 HD). A new 2-step decision tree was developed based on previous studies with another OCT device. In the first step, if at least 1 of the 4 independent parameters (pachymetry minimum, pachymetry minimum-median, pachymetry superonasal-inferotemporal, and epithelial superonasal-inferotemporal) overruns the cutoff values, the eye was suspicious for KC. In the second step, if the epithelial map showed concentric thinning and the thinnest point of the cornea and epithelium is coincident, the eye was classified as keratoconic.

RESULTS

172 manifest keratoconic eyes (108 patients), 21 subclinical keratoconic eyes (20 patients), and 172 normal eyes (90 age-matched participants) were included in this study. Step 1 captured 100% of manifest and subclinical keratoconic eyes. Step 2 ruled out all suspicious but normal cases and, falsely, 2 subclinical keratoconic eyes. Our 2-step decision tree reached 100% specificity, 100% sensitivity in manifest KC, and 90.4% sensitivity in subclinical KC.

CONCLUSIONS

Pachymetric and epithelial map parameters and patterns in OCT can be used in the diagnosis of KC, including subclinical cases, yielding a high level of agreement with the commonly used diagnostic reference, the Belin-Ambrosio display. Further improvements by refining our algorithm and including an automated evaluation in the software are desirable.

Reliability of Corneal, Epithelial, and Stromal Thickness Mapping for a 9-mm Zone Using Spectral-Domain Optical Coherence Tomography

PURPOSE

To evaluate the reliability of spectral-domain optical coherence tomography (SD-OCT; RTVue XR; Optovue, Inc., Fremont, CA, USA) for thickness mapping of the entire cornea (CT), corneal epithelium (ET). and corneal stroma (ST) over a 9-mm zone in healthy eyes. We sought to develop reference values for different age groups and elucidate potential sex- and age-dependent characteristics of corneal sublayer pachymetry maps.

METHODS

Three consecutive SD-OCT scans were obtained in 166 healthy right eyes (mean age = 50 ± 20 years). The thickness maps contain 25 sectors over a 9-mm diameter zone. To test measurement reliability, intraclass correlation coefficients (ICC), coefficients of variation (CoV), and within-subject standard deviations (WSSD) were calculated.

RESULTS

CT, ET, and ST ICCs ranged from 0.961 to 0.998, 0.896 to 0.945, and 0.955 to 0.998, respectively. CoV values for CT, ET, and ST ranged between 0.3 and 1.5%, 1.6 and 4.2%, and 0.4 and 1.7%, respectively. WSSD ranged from 6 to 41, 4 to 8, and 7 to 46 µm, respectively. A negative correlation was found between age and ET (p < 0.05) but not between age and ST or CT. No gender-related differences in CT, ET, or ST were detected. CoV of CT, ET, and ST measurements showed a positive correlation with age in 28, 64, and 28% of the sectors, respectively.

CONCLUSION

SD-OCT is a rapid and noninvasive technique that provides excellent reliability for corneal sublayer thickness measurements over a 9-mm zone. The reliability of the ET measurement seems to be negatively affected by age. Peripheral CT and global ET thin with age.

Corneal Epithelial Thickness Profile in Healthy Portuguese Children by High-Definition Optical Coherence Tomography

Introduction and Objective

To evaluate corneal epithelial thickness (ET) and corneal thickness (CT) profiles in healthy eyes of Portuguese children and provide information to establish the first normative Caucasian database for these age group.

Methods

Sixty healthy eyes of 60 children aged between 8 and 18 were evaluated using the Cirrus high-definition optical coherence tomography device. The average ET and CT were assessed using Cirrus Review Software with predefined concentric corneal ring-shaped zones. Specific regions of ET (central, superior, inferior, temporal, nasal, superonasal, inferotemporal, superotemporal and inferonasal) were also assessed. The mean ET, the mean CT and the difference of ET in corresponding octants were compared by gender. Correlations between central epithelial thickness (CET), age and refractive error were evaluated.

Results and Discussion

The average ET was lower in the peripheric zones, whereas the average CT was higher. ET was thinner in the superior area than in the inferior (p<0.05). ET was thicker in boys than in girls (p<0.05), but CT did not differ. CET was not correlated with older age or refractive error.

Conclusion

Optical coherence tomography analysis of ET reveals that it is thinner in the periphery, where the CT is thicker. Unlike CT, ET seems to be influenced by gender. ET profile proved to be a useful tool in keratoconus diagnosis and subclinical keratoconus detection in adults. As epithelial changes occur early in the disease and keratoconus is more aggressive in pediatric population, a normative database of ET profile could contribute to enhance early recognition of the disease in this age group.

Multimodal Photoacoustic Imaging-Guided Regression of Corneal Neovascularization: A Non-Invasive and Safe Strategy

Corneal neovascularization (CNV) is one of the main factors that induce blindness worldwide. However, current medical treatments cannot achieve non-invasive and safe inhibition of CNV. A noninvasive photoacoustic imaging (PAI)-guided method is purposed for the regression of CNV. PAI can monitor the oxygen saturation of cornea blood vessels through the endogenous contrast of hemoglobin and trace administrated drugs by themselves as exogenous contrast agents. An indocyanine green (ICG)-based nanocomposite (R-s-ICG) is prepared for CNV treatment via eye drops and subconjunctival injections. It is demonstrated that R-s-ICG can enrich corneal tissues and pathological blood vessels rapidly with minor residua in normal eyeball tissues. Anti-CNV treatment-driven changes in the blood vessels are assessed by real-time multimodal PAI in vivo, and then a safe laser irradiation strategy through the canthus is developed for phototherapy and gene therapy synergistic treatment. The treatment leads to the efficient inhibition of CNV with faint damages to normal tissues.

Wide Stromal Mapping Using an Anterior Segment Optical Coherence Tomography

Purpose

To quantify and assess the reproducibility of the corneal stromal thickness profiles captured by the SD-OCT. Secondly, we correlated the zonal thicknesses to the age, gender and axial length.

Methods

We included 227 normal eyes of 227 patients with a maximum hypermetropia of +5 and myopia of –6 diopters (D). Subjects with an intraocular pressure exceeding 22 mm Hg, evidence of cataract formation, history of ophthalmic surgery or disease were excluded. Lastly, reproducibility was evaluated in a subset of 50 participants by means of an identical scan protocol repeated by 2 different OCT operators.

Results

Stromal values were consistently thicker in the peripheral cornea (p<0.001). Age was negatively correlated with approximately every sector of the stroma with notable exceptions of the center (r=0.117, p=0.088) and the superior inner (r=0.057, 0.409), middle (r=0.086, p=0.209) and outer locations (r=0.120, p=0.079). There was no statistical significance in most sectors when looking at the axial length, gender and K1/K2. This method was highly reproducible in terms of both the ICC and COV.

Conclusion

Corneal stromal mapping is highly reproducible and shows a negative correlation to age. Additionally, the periphery of the stroma is consistently thicker to the center. Other variables like gender and axial length show no relationship to the corneal stroma.