Correlation between epithelial thickness in normal corneas, untreated ectatic corneas, and ectatic corneas previously treated with CXL; is overall epithelial thickness a very early ectasia prognostic factor?

Topographic Keratoconus Incidence in Greece Diagnosed in Routine Consecutive Cataract Procedures: A Consecutive Case Series of 1250 Cases over 5 Years

Background: Scheimpflug tomography has for many years been an integral part of our pre-operative assessment in cataract extraction. We retrospectively reviewed the incidence of topographic keratoconus and keratoconus suspicion in our routine cataract surgery population over 5 years. Setting: The Laservision Clinical and Research Institute, Athens, Greece. Methods: In 1250 consecutive cataract surgery cases in otherwise naïve eyes, accounting for years 2017 to 2021, we retrospectively evaluated preoperative Pentacam HR imaging. The cases already classified as keratoconus were included in group A. The residual cases were assessed by five different experienced evaluators (two ophthalmic surgeons and three optometrists) for topographic and tomographic keratoconus suspicion based on irregular pachymetry distribution, astigmatism truncation, and/or astigmatic imaging irregularity and included in group B. Regular corneas, by this assessment, were included in group C; irregular corneas, as determined by the evaluators but unrelated to keratoconus, were included in group D. Results: Based on the above, 138 cases (11.08%) were classified by Pentacam tomography as keratoconus and by default were included in group A. Of the residual cases, 314 or 25.12% were classified as suspect keratoconus and included in group B; 725 cases (58%) were classified as normal and non-keratoconus and included in group C; and 73 cases or 5.84% were placed in group D as non-keratoconus but abnormal. There was no disagreement between the five evaluators over any of the cases in groups C and D, and little variance among them for cases included in group B (less than 5% by ANOVA). Conclusions: The incidence of keratoconus and corneas suspicious for keratoconus in Greece appears to be much higher than respective reports from other regions: one in ten Greeks appear to have topographic keratoconus, most not diagnosed even by the age of cataract surgery, and almost an additional one in four may have suspicious corneal imaging for keratoconus. These data strongly imply that routine screening for disease should be promoted among Greeks, especially during puberty, to halt possible progression; moreover, careful screening should be performed when laser vision correction is being considered.

Comparison of different corneal imaging modalities using artificial intelligence for diagnosis of keratoconus: a systematic review and meta-analysis

PURPOSE

This review was designed to compare different corneal imaging modalities using artificial intelligence (AI) for the diagnosis of keratoconus (KCN), subclinical KCN (SKCN), and forme fruste KCN (FFKCN).

METHODS

A comprehensive systematic search was conducted in scientific databases, including Web of Science, PubMed, Scopus, and Google Scholar based on the PRISMA statement. Two independent reviewers assessed all potential publications on AI and KCN up to March 2022. The Critical Appraisal Skills Program (CASP) 11-item checklist was used to evaluate the validity of the studies. Eligible articles were categorized into three groups (KCN, SKCN, and FFKCN) and included in the meta-analysis. The pooled estimate of accuracy (PEA) was calculated for all selected articles.

RESULTS

The initial search yielded 575 relevant publications, of which 36 met the CASP quality criteria and were included in the analysis. Qualitative assessment showed that Scheimpflug and Placido combined with biomechanical and wavefront evaluations improved KCN detection (PEA, 99.2, and 99.0, respectively). The Scheimpflug system (92.25 PEA, 95% CI, 94.76-97.51) and a combination of Scheimpflug and Placido (96.44 PEA, 95% CI, 93.13-98.19) had the highest diagnostic accuracy for the detection of SKCN and FFKCN, respectively. The meta-analysis outcomes showed no significant difference between the CASP score and accuracy of the publications (all P > 0.05).

CONCLUSIONS

Simultaneous Scheimpflug and Placido corneal imaging methods provide high diagnostic accuracy for early detection of keratoconus. The use of AI models improves the discrimination of keratoconic eyes from normal corneas.

Ray-Tracing Customization in Myopic and Myopic Astigmatism LASIK Treatments for Low and High Order Aberrations Treatment: 2-Year Visual Function and Psychometric Value Outcomes of a Consecutive Case Series

Purpose

The safety and long-term efficacy of automated ray-tracing customized myopic and myopic astigmatic femtosecond laser-assisted LASIK.

Methods

This consecutive case series retrospective analysis, of 20 subjects (40 eyes) treated with automated raytracing named Wavelight Plus, to include low and high order aberrations based on a three-dimensional custom virtual eye for each case-calculated from interferometry data-obtained from a single diagnostic device that also provides Hartman-Shack Wavefront and Scheimpflug tomography data. We evaluated before and after the customized LASIK procedure: visual acuity, refractive error, high order aberrations, contrast sensitivity, and psychometric post-operative visual function data.

Results

At 24 months, the comparison of the pre-operative to the post-operative refractive and visual function value changes in average were: subjective manifest refraction from -4.38 ± 2.54 diopters (D) (range -9.75 to -1.25 D) to +0.11 ± 0.19 D; subjective manifest refractive astigmatism from -0.76 ± 0.91 D (range -2.75 to 0 D) to -0.13 ± 0.16 D, corneal astigmatism from -1.16 ± 0.64 D (range -0.2 to -2.8) to -0.47 ± 0.11 D. 65% of the eyes studied demonstrated an increase of at least one line of vision, while from the same group 38% demonstrated 2 lines of increase. High order aberrations, contrast sensitivity as well as the subjective psychometric input based on the VFQ-25 questionnaire demonstrated actual improvement.

Conclusion

This longer-term follow-up, single-arm retrospective consecutive case series documents LASIK treatment customization that appears to be safe and effective in the correction of myopia and myopic astigmatism. Markedly improved objective and subjective visual function post-operatively, underlying the potential importance of simultaneously attempting to correct high order aberrations and improving the spatial alignment of total, measured human eye optics.

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.

Assessing progression limits in different grades of keratoconus from a novel perspective: precision of measurements of the corneal epithelium

BACKGROUND

To assess repeatability and reproducibility of corneal epithelium thickness (ET) measured by a spectral-domain optical coherence tomographer (SD-OCT)/Placido topographer (MS-39, CSO, Florence, Italy) in keratoconus (KC) population at different stages, as well as to determine the progression limits for evaluating KC progression.

METHODS

A total of 149 eyes were enrolled in this study, with 29 eyes in the forme fruste keratoconus (FFKC) group, 34 eyes in the mild KC group, 40 eyes in the moderate KC group, and 46 eyes in the severe KC group. Employing the within-subject standard deviation (Sw), test-retest variability (TRT), coefficient of variation (CoV), and intraclass correlation coefficient (ICC) to evaluate intraoperator repeatability and interoperator reproducibility.

RESULTS

The repeatability and reproducibility of MS-39 in patients with KC were acceptable, according to ICC values ranging from 0.732 to 0.954. However, patients with more severe KC and progressive peripheralization of the measurement points had higher TRTs but a thinning trend. The current study tended to set the cut-off values of mild KC, moderate KC, and severe KC to 4.9 µm, 5.2 µm, and 7.4 µm for thinnest epithelium thickness (TET). When differences between follow-ups are higher than those values, progression of the disease is possible. As for center epithelium thickness (CET), cut-off values for mild KC, moderate KC, and severe KC should be 2.8 µm, 4.4 µm, and 5.3 µm. This might be useful in the follow-up and diagnosis of keratoconus.

CONCLUSIONS

This study demonstrated that the precision of MS-39 was reduced in measuring more severe KC patients and more peripheral corneal points. In determining disease progression, values should be differentiated between disease-related real changes and measurement inaccuracies. Due to the large difference in ET measured by MS-39 between various stages of disease progression, it is necessary to accurately grade KC patients to avoid errors in KC clinical decision-making.

Keratoconus: exploring fundamentals and future perspectives - a comprehensive systematic review

Background

New developments in artificial intelligence, particularly with promising results in early detection and management of keratoconus, have favorably altered the natural history of the disease over the last few decades. Features of artificial intelligence in different machine such as anterior segment optical coherence tomography, and femtosecond laser technique have improved safety, precision, effectiveness, and predictability of treatment modalities of keratoconus (from contact lenses to keratoplasty techniques). These options ingrained in artificial intelligence are already underway and allow ophthalmologist to approach disease in the most non-invasive way.

Objectives

This study comprehensively describes all of the treatment modalities of keratoconus considering machine learning strategies.

Design

A multidimensional comprehensive systematic narrative review.

Data sources and methods

A comprehensive search was done in the five main electronic databases (PubMed, Scopus, Web of Science, Embase, and Cochrane), without language and time or type of study restrictions. Afterward, eligible articles were selected by screening the titles and abstracts based on main mesh keywords. For potentially eligible articles, the full text was also reviewed.

Results

Artificial intelligence demonstrates promise in keratoconus diagnosis and clinical management, spanning early detection (especially in subclinical cases), preoperative screening, postoperative ectasia prediction after keratorefractive surgery, and guiding surgical decisions. The majority of studies employed a solitary machine learning algorithm, whereas minor studies assessed multiple algorithms that evaluated the association of various keratoconus staging and management strategies. Last but not least, AI has proven effective in guiding the implantation of intracorneal ring segments in keratoconus corneas and predicting surgical outcomes.

Conclusion

The efficient and widespread clinical translation of machine learning models in keratoconus management is a crucial goal of potential future approaches to better visual performance in keratoconus patients.

Trial registration

The article has been registered through PROSPERO, an international database of prospectively registered systematic reviews, with the ID: CRD42022319338.

Discrimination between keratoconus, forme fruste keratoconus, and normal eyes using a novel OCT-based tomographer

PURPOSE

To combine objective machine-derived corneal parameters obtained with new swept-source optical coherence tomography (SS-OCT) tomographer (Anterion) to differentiate between normal (N), keratoconus (KC) and forme fruste KC (FFKC).

SETTING

Laser Center, Hôpital Fondation Adolphe de Rothschild, Paris, France.

DESIGN

Retrospective study.

METHODS

281 eyes of 281 patients were included and divided into 3 groups: N (n = 156), FFKC (n = 43), and KC (n = 82). Eyes were included in each group based on objective evaluation using Nidek Corneal Navigator, and subjective evaluation by authors. The SS-OCT system provided anterior and posterior corneal surface and pachymetry derived variables. The training set was composed of 143 eyes (95 N, 43 FFKC). Discriminant analysis was used to determine the group of an observation based on a set of variables. The obtained formula was tested in the validation set composed of 61 N and 82 KC.

RESULTS

Among curvature parameters, the FFKC had significantly higher irregularity index at 3 mm and 5 mm, higher inferior-superior index, higher SteepK-OppositeK index and inferiorly decentered posterior steepest keratometry. Among thickness parameters: central pachymetry, thinnest pachymetry, percentage of thickness increase from center to periphery, and inferior decentration of the thinnest point were statistically different between groups. Combination of multiple variables into a discriminant function (F1) included 5 parameters and reached an area under the receiver operating characteristic curve (AUROC) of 0.95 (sensitivity = 75%, specificity = 98.5%) for detection of FFKC. F1 differentiates N from KC with AUROC = 0.99 (sensitivity = 99%, specificity = 99%).

CONCLUSIONS

Combining anterior and posterior curvatures variables along with pachymetric data obtained from SS-OCT allowed automated detection of early KC and KC with very good accuracy (87% and 99.5% respectively).

Keratoconus Diagnosis: From Fundamentals to Artificial Intelligence: A Systematic Narrative Review

The remarkable recent advances in managing keratoconus, the most common corneal ectasia, encouraged researchers to conduct further studies on the disease. Despite the abundance of information about keratoconus, debates persist regarding the detection of mild cases. Early detection plays a crucial role in facilitating less invasive treatments. This review encompasses corneal data ranging from the basic sciences to the application of artificial intelligence in keratoconus patients. Diagnostic systems utilize automated decision trees, support vector machines, and various types of neural networks, incorporating input from various corneal imaging equipment. Although the integration of artificial intelligence techniques into corneal imaging devices may take time, their popularity in clinical practice is increasing. Most of the studies reviewed herein demonstrate a high discriminatory power between normal and keratoconus cases, with a relatively lower discriminatory power for subclinical keratoconus.

Epithelial Thickness Mapping in Keratoconic Corneas: Repeatability and Agreement Between CSO MS-39, Heidelberg Anterion, and Optovue Avanti OCT Devices

PURPOSE

To assess repeatability and agreement of corneal epithelial thickness mapping in eyes with keratoconus using three optical coherence tomography (OCT) devices featuring different technologies: spectral-domain (SD) OCT combined with Placido disk corneal topography (MS-39), swept-source OCT (Anterion), and SD-OCT (Avanti).

METHODS

Three consecutive measurements were acquired with the three devices in 60 eyes with keratoconus. The mean epithelial thickness was calculated in the central 2-mm zone and in 2- to 5-mm and 5- to 7-mm diameter rings. The repeatability was calculated using pooled within-subject standard deviation (Sw). The agreement was assessed by paired t tests and Bland-Altman plots.

RESULTS

The repeatability (Sw) of the epithelial thickness for the central 2-mm zone was 0.91, 0.71, and 0.93 μm for the MS-39, Anterion, and Avanti, respectively. All thicknesses with the MS-39 were greater than those of the Anterion and Avanti, with mean differences of 4.11 ± 1.34 μm (P < .001) and 0.52 ± 1.30 μm (P = .003), respectively. The 95% limits of agreement were 1.484 to 6.736 μm for the MS-39 and Anterion, -3.068 to 2.028 μm for the Avanti and MS-39, and 1.258 to 5.922 μm for for the Avanti and Anterion.

CONCLUSIONS

Epithelial thickness mapping results were most repeatable with the Anterion, followed by the MS-39 and Avanti. The MS-39 gave the thickest values, followed by the Avanti and Anterion. The differences were significant, making the devices not interchangeable for epithelial thickness mapping in eyes with keratoconus. [J Refract Surg. 2023;39(7):474-480.].

Comparison of ocular surface assessment outcomes between healthy controls and patients with obstructive sleep apnea-hypopnea syndrome: a meta-analysis of the literature

Objective: This meta-analysis aims to determine whether ocular surface alterations are associated with disease severity in patients with obstructive sleep apnea-hypopnea syndrome (OSAHS). Methods: The protocol for this systematic review and meta-analysis was registered in PROSPERO. We conducted the search in six electronic databases (China National Knowledge Infrastructure, EMBASE, Cochrane Library, Web of Science, Wanfang, and PubMed) from since the construction of the databases to 30 December 2022. The standard mean difference (SMD) and correlation coefficients are reported as measures of the effect size in the presence of retrieved data. In addition, the random effects model or fixed effects model was used in a combined analysis. Stata 11.0 and R 3.6.1 were used for statistical analyses of the data. Results: A total of 15 studies satisfied the inclusion criteria for this study. The prevalence of floppy eyelid syndrome (FES) and dry eye syndrome in patients with obstructive sleep apnea-hypopnea syndrome was 40 and 48%, respectively. In addition, the Schirmer 1 value and tear break-up time (TBUT) were remarkably reduced in patients with OSAHS when compared to that of the controls. The ocular surface disease index (OSDI) scores, Oxford corneal staining scores, and the rates of loss in the meibomian glands were elevated in patients with obstructive sleep apnea-hypopnea syndrome when compared to that of the controls, especially those with severe disease. Moreover, the Schirmer 1 value and tear break-up time exhibited a negative correlation with the apnea-hypopnea index (AHI), and the OSDI showed a positive association with the apnea-hypopnea index. Conclusion: Patients with OSAHS had a greater prevalence of FES than the healthy controls. They also showed lower Schirmer 1 value and tear break-up time but had a higher OSDI, Oxford corneal staining scores, and rates of loss in the meibomian glands than the healthy controls. Clinical Trial Registration: (https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=392527).

Comparison of corneal measurements in normal and keratoconus eyes using Anterior Segment Optical Coherence Tomography (AS-OCT) and Pentacam HR topographer

BACKGROUND

Keratoconus (KC) is easily recognized by its unique topographic pattern, but it can be difficult to distinguish subclinical form of the disease from the normal cornea. Optovue anterior segment optical coherence tomography (AS-OCT) helps diagnose KC.

AIM OF THE WORK

To assess and the level of agreement of Keratometry-readings (K), Central Corneal Thickness (CCT) and Thinnest Corneal Thickness (TCT) measurements obtained by Optovue AS-OCT and Wavelight Oculyzer Pentacam HR in two groups: KC eyes and normal eyes.

PATIENTS AND METHODS

This is a prospective clinical observational study. The study included 110 eyes divided into two groups. The study group included 62 eyes with topographic evidence of KC. The control group included 48 eyes of normal subjects with no topographic evidence of KC. All of the participants underwent full cycloplegic refraction, spectacle best-corrected distance visual acuity, comprehensive slit-lamp biomicroscopy and fundoscopy. All participants underwent corneal topography by Pentacam HR and AS-OCT.

RESULTS

There were highly significant differences between the studied groups as regarding BCVA, intraocular pressure and CCT measurements which were found to be lower among KC group compared to the control one. There were highly significant differences between the studied groups regarding TCT measurement detected by Pentacam HR and AS-OCT which was found to be lower among the keratoconus group compared to the control one (470.9, 455.7 versus 541.9 and 518.7 respectively).

CONCLUSION

Both Scheimpflug-based imaging and AS-OCT provide comparable readings with a good agreement regarding corneal pachymetry in keratoconus group with accurate identification of KC eyes and healthy ones. However, there was a significant difference in K readings between both devices in Keratoconus and control group.

Role of corneal epithelial thickness during myopic regression in femtosecond laser-assisted in situ keratomileusis and transepithelial photorefractive keratectomy

BACKGROUND

The study aimed to investigate the relationship between changes in corneal epithelial thickness and the outcome of myopic regression after femtosecond laser-assisted in situ keratomileusis (FS-LASIK) and transepithelial photorefractive keratectomy (TPRK).

METHODS

This study included 45 eyes of 25 patients undergoing FS-LASIK and 44 eyes of 24 patients undergoing TPRK. Myopic regression occurred in these patients postoperatively from 8 to 21 months. The corneal epithelial thickness was measured using a spectral-domain optical coherence tomography at the onset of regression, 3 months after treatment, and 3 months after drug withdrawal.

RESULTS

Compared with that of preoperation, corneal epithelial thickness increased when regression occurred in both groups (all P < 0.05). The thickness of central corneal epithelium in FS-LASIK and TPRK groups reached 65.02 ± 4.12 µm and 61.63 ± 2.91 µm, respectively. The corneal epithelial thickness decreased when myopic regression subsided after 3 months of steroid treatment compared to the onset (P < 0.05). With a decrease in corneal epithelial thickness, the curvature of the anterior corneal surface, central corneal thickness, and refractive power all decreased (all P < 0.05). The corneal epithelial thickness and refractive error remained relatively stable after 3 months of treatment withdrawal (P > 0.05).

CONCLUSION

The corneal epithelial thickness determined the outcome of myopic regression similarly in FS-LASIK and TPRK. When the corneal epithelium thickened, regression occurred. After steroid treatment, epithelial thickness decreased whereas regression subsided.

Corneal epithelium in keratoconus underexpresses active NRF2 and a subset of oxidative stress-related genes

Keratoconus (KC) is a multifactorial progressive ectatic disorder characterized by local thinning of the cornea, leading to decreased visual acuity due to irregular astigmatism and opacities. Despite the evolution of advanced imaging methods, the exact etiology of KC remains unknown. Our aim was to investigate the involvement of corneal epithelium in the pathophysiology of the disease. Corneal epithelial samples were collected from 23 controls and from 2 cohorts of patients with KC: 22 undergoing corneal crosslinking (early KC) and 6 patients before penetrating keratoplasty (advanced KC). The expression of genes involved in the epidermal terminal differentiation program and of the oxidative stress pathway was assessed by real time PCR analysis. Presence of some of the differentially expressed transcripts was confirmed at protein level using immunofluorescence on controls and advanced KC additional corneal samples. We found statistically significant under-expression in early KC samples of some genes known to be involved in the mechanical resistance of the epidermis (KRT16, KRT14, SPRR1A, SPRR2A, SPRR3, TGM1 and TGM5) and in oxidative stress pathways (NRF2, HMOX1 and HMOX2), as compared to controls. In advanced KC samples, expression of SPRR2A and HMOX1 was reduced. Decreased expression of keratin (KRT)16 and KRT14 proteins was observed. Moreover, differential localization was noted for involucrin, another protein involved in the epidermis mechanical properties. Finally, we observed an immunofluorescence staining for the active form of NRF2 in control epithelia that was reduced in KC epithelia. These results suggest a defect in the mechanical resistance and the oxidative stress defense possibly mediated via the NRF2 pathway in the corneal keratoconic epithelium.

Corneal Epithelium Asymmetry in Children With Atopy: The Effect of Hand Dominance

Purpose

To evaluate the effect of eye rubbing on the epithelial thickness profile in tomographically normal corneas by AS-OCT and to compare right and left eyes in right-handed children.

Methods

Thirty right-handed boys (mean age 11.2 years) with ocular allergy and history of eye rubbing were evaluated using Scheimpflug (Pentacam HR, Oculus Wetzlar, Germany) and anterior segment optical coherence tomography. Epithelial thickness (ET) and full corneal thickness (CT) parameters were compared between right and left eyes with a non-parametric Mann–Whitney test. A p-value lower than 0.05 was considered for statistical significance.

Results

No eyes had topometric nor tomographic criteria for keratoconus. The min-max ET was lower in right eyes (−2.8 µm vs −3.5; p = 0.02). The difference between inferior and superior (I-S) octants was lower in right eyes (1.1 µm vs 1.9 µm; p = 0.03) as a result of inferotemporal thinning. The highest ET difference was registered between nasal and temporal octants and was more pronounced in the right eyes (2 µm vs 3.1 µm; p < 0.001).

Conclusion

AS-OCT analyses reveal different epithelial thickness patterns between the eyes in young atopic patients, likely eye rubbers. Inferior and temporal epithelial thickness seem to be more affected by thinning in the eye on the side of the dominant hand.

Applications of epithelial thickness mapping in corneal refractive surgery

In this review, we discuss the applications of epithelial thickness mapping in corneal refractive surgery. The review describes that the epithelial thickness profile is nonuniform in the normal eye, being thinner superiorly than inferiorly and thinner temporally than nasally. It is postulated that this is due to the eyelid forces and blinking action on the superior cornea. Changes in the epithelial thickness profile have been found to be highly predictable, responding to compensate for changes in the stromal curvature gradient, using the eyelid as an outer template. This leads to characteristic changes in the epithelial thickness profile that can be used for early screening in keratoconus, postoperative monitoring for early signs of corneal ectasia, and for determining whether further steepening can be performed without the risk of apical syndrome following primary hyperopic treatment. Compensatory epithelial thickness changes are also a critical part of diagnosis in irregular astigmatism as these partially mask the stromal surface irregularities. The epithelial thickness map can then be used to plan a trans-epithelial photorefractive keratectomy treatment for cases of irregularly irregular astigmatism.

Epithelial thickness mapping for corneal refractive surgery

PURPOSE OF REVIEW

As more devices become available that offer corneal epithelial thickness mapping, this is becoming more widely used for numerous applications in corneal refractive surgery.

RECENT FINDINGS

The epithelial thickness profile is nonuniform in the normal eye, being thinner superiorly than inferiorly and thinner temporally than nasally. Changes in the epithelial thickness profile are highly predictable, responding to compensate for changes in the stromal curvature gradient, using the eyelid as an outer template. This leads to characteristic changes that can be used for early screening in keratoconus, postoperative monitoring for early signs of corneal ectasia, and for determining whether further steepening can be performed without the risk of apical syndrome following primary hyperopic treatment. Compensatory epithelial thickness changes are also a critical part of diagnosis in irregular astigmatism as these partially mask the stromal surface irregularities. The epithelial thickness map can then be used to plan a trans-epithelial PRK treatment for cases of irregularly irregular astigmatism. Other factors can also affect the epithelial thickness profile, including dry eye, anterior basement membrane dystrophy and eyelid ptosis.

SUMMARY

Epithelial thickness mapping is becoming a crucial tool for refractive surgery, in particular for keratoconus screening, ectasia monitoring, hyperopic treatment planning, and therapeutic diagnosis and treatment.

Differentiating Between Contact Lens Warpage and Keratoconus Using OCT Maps of Corneal Mean Curvature and Epithelial Thickness

PURPOSE

To formulate an Epithelial Modulation index to differentiate between eyes with contact lens warpage and keratoconus.

METHODS

Normal eyes and eyes with either contact lens warpage or keratoconus were scanned by a Fourier-domain optical coherence tomography (OCT) system. Maps of epithelial thickness and anterior surface mean curvature were generated and converted to deviation maps by subtracting the average maps from a healthy population. The Epithelial Modulation index was defined as the covariance between the two types of deviation maps. A logistic regression model was used to classify eyes as non-keratoconus (normal or warp-age) or keratoconus (manifest, subclinical, or forme fruste).

RESULTS

The average Epithelial Modulation index value for normal eyes was -0.6 ± 1.0 µm/m. Eyes with keratoconus were characterized by coincident high anterior surface mean curvature and low epithelial thickness, resulting in a high Epithelial Modulation index (manifest: 103.0 ± 82.9 µm/m, subclinical: 37.0 ± 23.0 µm/m, forme fruste: 7.3 ± 13.2 µm/m). The Epithelial Modulation index was closer to normal for eyes with warpage (-1.9 ± 4.0 µm/m). The classification accuracy of the Epithelial Modulation index during five-fold cross-validation of the logistic regression model was 100 ± 0% for normal eyes and 99.0 ± 2.0% for eyes with warpage. The accuracy was 100 ± 0%, 100 ± 0%, and 53.1 ± 1.5% for the manifest, subclinical, and forme fruste keratoconus groups, respectively.

CONCLUSIONS

The Epithelial Modulation index is useful in distinguishing eyes with secondary epithelial modulation (keratoconus) from those with primary epithelial deformation (contact lens-related warpage). [J Refract Surg. 2022;38(2):112-119.].

The detection of keratoconus using novel metrics derived by anterior segment optical coherence tomography

PURPOSE

To determine through a feasibility study whether anterior and posterior corneal arc length and cross-sectional area measured using anterior segment ocular coherence tomography (AS-OCT) can distinguish between healthy and keratoconic corneas.

METHODS

Patients diagnosed with keratoconus along with healthy controls underwent AS-OCT. ImageJ was used to determine the central 6 mm anterior and posterior corneal arc lengths and cross-sectional areas. Each length and area was then divided into 1-mm segment and relative differences compared.

RESULTS

Twenty-five eyes from 15 patients with keratoconus, along with 25 eyes from 14 healthy controls were enrolled. There was a statistically significant difference in anterior and posterior corneal arc lengths as well as corneal cross-sectional area (p = 0.006, p = 0.005, p = 0.01, respectively). When selecting for the less advanced keratoconus eye, it was noted that posterior corneal arc length was longer in the paracentral temporal segment (1003 vs. 1010 µm, p = 0.04) and that greater change in corneal cross-sectional areas occurred between adjacent segments in less advanced keratoconus eyes.

CONCLUSION

AS-OCT is capable of reliably measuring corneal arc lengths in patients with keratoconus and healthy patients. Both anterior and posterior corneal arc lengths along with central cross-sectional areas are statistically different between healthy and keratoconus eyes.

Anterior Segment Optical Coherence Tomography of Tear Film and Cornea in Systemic Lupus Erythematosus Patients

Purpose

To study tear film and corneal thickness measurements in systemic lupus erythematosus (SLE) patients compared to age-matched controls using anterior segment optical coherence tomography (AS-OCT).

Methods

This was a cross-sectional study. Study participants were divided into 3 groups: Group A: SLE patients with clinical dry eye, Group B: SLE patients without clinical dry eye and Group C: healthy controls. The lower tear meniscus parameters measured using AS-OCT were tear meniscus height (TMH), tear meniscus depth (TMD) and tear meniscus area (TMA). The central corneal and corneal epithelial thickness were automatically calculated.

Results

The study included 40 eyes in Group A, 60 in Group B, and 100 in Group C. Mean age was 26.9±6.6 years for Group A, 27.6±7.3 years for Group B and 35.7±9.2 years for Group C (p= 0.06). All subjects were females except for 1 male patient in Group A. Mean TMH, TMA and TMD in Group C were 487.7±185.6 µm, 0.068±0.040 mm², and 341.2±99.1 µm, respectively, which was significantly higher compared to Group A (225.5±27.9 µm, 0.018±0.004 mm² and 171.9±26.0 µm, respectively, all p < 0.001) and Group B (395.4±118.8 µm, p < 0.001; 0.05±0.04 mm², p=0.016 and 280.6±93.4 µm, p < 0.001, respectively). Group B eyes also had significantly higher parameters compared to Group A (all p < 0.001). Mean corneal and epithelial thickness in Group C were 501.6±37.5 µm and 53.3±4.5 µm, respectively, which was significantly higher compared to Group A (496.1±24.1 µm, p=0.044 and 49.5±3.5 µm, p < 0.001, respectively) and Group B (504.2±22.03 µm, p=0.046 and 47.5±5.6 µm, p < 0.001, respectively). Group B eyes also had a significantly higher corneal thickness (p=0.031) and epithelial thickness (p=0.011) compared to Group A.

Conclusion

We demonstrated significant reduction of tear meniscus dimensions, central corneal thickness and epithelial thickness in SLE patients compared to age-matched controls using AS-OCT.

Postoperative Corneal Epithelial Remodeling After Intracorneal Ring Segment Procedures for Keratoconus: An Optical Coherence Tomography Study

PURPOSE

To assess epithelial corneal remodeling by anterior segment optical coherence tomography (AS-OCT) after intracorneal ring segments (ICRS) implantation in keratoconic eyes.

METHODS

This prospective observational study included patients with keratoconus receiving ICRS of different arc lengths according to their tomographic pattern. AS-OCT and corneal topography (Scheimpflug camera) were performed before and 1, 3, and 6 months after surgery. Corneal pachymetry mapping was performed and total corneal and epithelial thicknesses (3-mm central and 16 points on 6-mm zone) were measured over the pupil center using AS-OCT. Topographic parameters were also assessed.

RESULTS

A total of 68 keratoconic eyes were analyzed (Amsler-Krumeich stages 1 to 4) in four groups of 17 eyes: 210° ICRS, 320° ICRS, double 160° ICRS, and single 160° ICRS. Corneal pachymetry mapping revealed that epithelial thickness increased significantly in the internal zones juxtaposed to the ICRS without smoothing during the postoperative period (P < .05). Mean maximum epithelial thickness increased from 67 ± 6 to 79 ± 7 µm for 210° ICRS, 66 ± 9 to 82 ± 4 µm for 320° ICRS, 63 ± 6 to 78 ± 7 µm for double 160° ICRS, and 62 ± 5 to 77 ± 5 µm for single 160° ICRS (P < .0001). Significant epithelial thickening at the apex of the cone was observed in all groups (P < .05).

CONCLUSIONS

Significant epithelial thickening occurs after ICRS implantation adjacent to the ICRS to compensate for the ridge created with a thickening of epithelium over the cone due to regularization of the stromal surface. [J Refract Surg. 2021;37(6):404-413.].

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.

Corneal epithelial thickness analysis of forme fruste keratoconus with optical coherence tomography

AIM

To explore the significance of corneal epithelial thickness analysis in diagnosing early keratoconus.

METHODS

There were 26 clinical keratoconus, 21 forme fruste keratoconus, 40 high corneal astigmatism (ΔK) and 40 low ΔK eyes involved in the study. Fourier-domain optical coherence tomography was used to measure the corneal epithelial thickness of four groups. The morphological features of topographic map and the thickness of corneal epithelial thinnest point were analyzed. The distribution curve of corneal epithelial thickness at 45°, 90°, and 135° axial directions that are through the pupil center was also analyzed. One-way ANOVA was performed to compare the data.

RESULTS

The topographic map of forme fruste keratoconus corneal epithelial thickness was uniformity shape; crater shape existed only in clinical keratoconus group; and central island shape mainly existed in high ΔK group. The thinnest point of corneal epithelial thickness of forme fruste keratoconus group was significantly lower than that of low ΔK group (P=0.022). The thickness of corneal epithelium in the forme fruste keratoconus at 90° was thinner than that in the low astigmatism group at -1, and -2 mm points (P _{-1 mm}=0.015, P _{-2 mm}=0.036).

CONCLUSION

The analysis of the thinnest point in forme fruste keratoconus corneal epithelium appears earlier than corneal epithelial remodeling. The topographic map of corneal epithelium in high ΔK eyes appears in central island shape, and can be used for the differential diagnosis of early keratoconus.

The Influence of Tomographic Corneal Characteristics on Epithelial Thickness Profile

Purpose

To understand the influence of tomographic corneal characteristics on the epithelium of normal eyes.

Methods

We scanned a total of 98 eyes of 98 individuals using anterior segment tomography and a spectral-domain optical coherence tomography (OCT) epithelial mapping tool. Only eyes with no previous pathology were included, with a refractive range of +5 diopters (D) to -6 D, intraocular pressure of < 22 mmHg, and no evidence of dry eye (Schirmer’s test 2 value > 5 mm). Corneal curvature metrics were statistically correlated with regional epithelial thickness parameters.

Results

The anterior and posterior corneal surface flat and steep axis, the maximum and minimum curvature, corneal topographic astigmatism, astigmatism polar values, and corneal volume had no statistically significant correlation (p>0.05) with the epithelial thickness. Similarly, anterior corneal surface asphericity had no significant correlation. Posterior surface asphericity had a statistically significant moderate correlation with the epithelium in all areas. Similar results were seen in the multivariate analysis.

Conclusions

None of the front or back surface parameters had any influence on the corneal epithelium except for the posterior surface asphericity. This statistically significant yet clinically insignificant correlation may be enhanced in diseased populations like keratoconus and could indicate epithelial remodeling with early posterior corneal changes.

Initial Outcomes with Customized Myopic LASIK, Guided by Automated Ray Tracing Optimization: A Novel Technique

Purpose

Safety and efficacy of a novel automated ray tracing optimization in customization of excimer ablation in myopic LASIK.

Methods

In a consecutive case series, 25 patients (50 eyes) undergoing femtosecond-laser-assisted myopic LASIK were evaluated. The novel, artificial-intelligence platform initially calculates the ablation profile based on a model eye for each case, based on interferometry axial length data. Low- and high-order aberration calculation is performed by raytracing based on wavefront and Scheimpflug tomography measurements, all from a single diagnostic device. Visual acuity, refractive error, keratometry, topography, high-order aberrations and contrast sensitivity were evaluated, over six months follow-up.

Results

Change from pre- to 6 months post-operative: mean refractive error improved from −5.06 ± 2.54 diopters (D) (range −8.0 to −0.50 D) to −0.11 ± 0.09 D (range −0.25 to + 0.25); refractive astigmatism from −1.07 ± 0.91 D (range −4.25 to 0 D) to −0.15 ± 0.04 D (range −0.25 to 0); and topographic astigmatism from −1.65 ± 0.85 D to −0.26 ± 0.11 D (range −0.60 to 0). About 65% of eyes gained one line of vision and 38% 2 lines. Pre- to post-operative high-order aberration average: RMSh changed from 0.25 um to 0.35 um. Contrast sensitivity improved post-operatively.

Conclusion

We report safe and effective preliminary outcomes with a novel excimer laser customization by ray tracing optimization, for myopic LASIK treatments, employing several independent up-till-now diagnostics and a customized eye model reference for each case. It bears the potential advantage through total eye aberration data and ray tracing refraction calculation to offer improved and more predictable visual outcomes.

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Scheimpflug vs Scanning-Slit Corneal Tomography: Comparison of Corneal and Anterior Chamber Tomography Indices for Repeatability and Agreement in Healthy Eyes

Purpose

To evaluate and compare the repeatability and agreement of Scheimpflug vs scanning-slit tomography of the cornea and the anterior chamber in terms of keratometric and tomographic indices in healthy eyes.

Methods

The 20 eyes of 10 healthy participants underwent 3 consecutive measurements using both Scheimpflug-tomography and scanning-slit tomography, diagnostic devices. Multiple corneal and anterior chamber tomographic parameters were recorded and evaluated to include corneal keratometry and its axis; corneal best-fit sphere (BFS), pachymetry mapping, angle kappa, anterior chamber depth (ACD), pupil diameter, and location. Repeatability for each device was assessed using the within each subject standard deviation of sequential exams, the coefficient variation (CV) and the intraclass correlation coefficient (ICC). Agreement between the two devices was assessed using Bland-Altman plots with 95% limits of agreement (LoA) and correlation coefficient (r).

Results

Both devices were found to have high repeatability (ICC>0.9) both in keratometric and other tomographic measurements. Scheimpflug tomography's repeatability though appeared superior in the average keratometry values, anterior and posterior BFS, thinnest corneal pachymetry value and location (p<0.05). Agreement: Statistically significant inter-device differences were noted in the mean values of K1, K2, BFS, ACD and thinnest corneal pachymetry (p<0.05). Despite the agreement differences noted, the two devices were well correlated (r>0.8) in respective measurements with Scheimpflug delivering consistently lower values than the scanning-slit tomography device.

Conclusion

Scheimpflug-tomography repeatability was found to be superior to that of scanning-slit tomography in this specific study, in most parameters evaluated. Inter-device agreement evaluation suggests that reading from the two devices may not be used interchangeably in absolute values, yet they are well correlated with Scheimpflug delivering consistently lower values in most.

Comparison of corneal epithelial thickness profile in dry eye patients, keratoconus suspect, and healthy eyes

PURPOSE

To compare the corneal epithelial thickness profile in patients with dry eyes and keratoconus suspect with normal healthy eyes.

METHODS

The study involved 120 eyes with an age range from 19 to 30 years. Forty eyes had normal corneal topography and no dry eyes. Forty eyes had dry eyes but had normal corneal topography. The last 40 eyes were keratoconus suspect and had no symptoms or signs of dry eyes.

RESULTS

Central epithelial thickness was not different statistically for all eyes. (p-value: 0.1). The superior epithelial thickness was 53.5 µm ±3.1 in the control group, 53.4 µm ±3.5 in the dry eye group, and 53.6 µm ±2.8 in the keratoconus suspect group. No statistically significant difference was found (p-value = 0.7). The inferior epithelial thickness was 55.7 µm ±3.5 in the control, 57.2 µm ±3.19 in the dry eyes, and 52.2 µm ±3.12 in the KC suspects. There was inferior thickening in the dry eyes and thinning in the KC suspects and this was statistically significant (p-value < 0.01). Minimum epithelial thickness was 52.8 µm ±2.91 in the control and 53.2 µm ±3.51 in the dry eyes and it was located superiorly for both groups. In the KC suspects, the minimum thickness was 52.3 µm ±3.19 and was located inferiorly.

CONCLUSION

In our study the epithelium appears to be thicker inferiorly in dry eyes and thinner in KC suspects. Displacement of thinnest location on epithelial map may be a helpful early sign of keratoconus. However, follow-up study is necessary to confirm the thinnest location displacement helped in this diagnosis.

Epithelial Remodeling Following Phacoemulsification in Diabetic Patients Using Anterior-Segment Optical Coherence Tomography: A Comparative Study

Purpose

To compare the effect of phacoemulsification on corneal epithelial thickness in diabetic and nondiabetic cataract patients.

Methods

Fifty eyes with cataracts were enrolled in a prospective comparative interventional study. They were divided into two groups: group A (diabetics) and group B (nondiabetics) and underwent uneventful phacoemulsification. Epithelial thickness was assessed in the central, paracentral, and peripheral cornea on the first day and at 1 week, 1 month, and 3 months postoperatively using spectral-domain ocular coherence tomography.

Results

A significant increase in the first-day postoperative central epithelial thickness was noticed in both groups (57.16±3.5 µm and 55.96±2.81 µm in groups A and B, respectively), with increased baseline epithelial thickness of 3.8±2.1 µm and 3.4±2.14 µm in groups A and B, respectively (P<0.001). A significant decrease in epithelial thickness was noticed in both groups after 1 week (−2.40±3.1 µm and −2.76±2.71 µm in group A and B, respectively). No further significant change was noticed in the nondiabetic group at 1 month; however, significant reductions in for central epithelial thickness were found in the diabetic group up to the first month (−0.80±1.9 µm, P=0.05). Central corneal thickness followed the same pattern of change as the epithelium. A nonsignificant delay in visual acuity improvement was noticed in diabetic patients.

Conclusion

Phacoemulsification induces a temporary increase in corneal and epithelial thickness that should resolve by the first week postoperatively. However, diabetic patients had slower epithelial recovery that took up to 1 month, which could be reflected in delayed visual recovery with no effect on the final visual outcome.

Measurement of refractive, wavefront, topographic, and keratometric changes attributable to epithelial removal in keratoconus

OBJECTIVE

The corneal epithelium is able to mask topographic and keratometric abnormalities of the underlying Bowman layer in keratoconus, but its contribution to refractive and wavefront parameters has not yet been studied. This study compared the refractive and aberrometric features of the corneal epithelium and Bowman layer in eyes with keratoconus before and after epithelial debridement.

METHODS

Corneal refractive and wavefront variables were measured in patients with keratoconus undergoing corneal crosslinking-immediately before and after epithelial debridement using a third-generation combined corneal topographer, autorefractor, and aberrometer.

RESULTS

After epithelial debridement, there were significant changes in spherical equivalent (-1.37 D; p < 0.01) and asphericity (-0.64; p = 0.03). The mean difference in the magnitude of epithelium-induced astigmatism in the 3rd and 5th central millimeter rings was 0.44 ± 3.20 D × 8 and 0.43 ± 2.75 D × 21 (positive cylinder), respectively. Corneal astigmatism axis shifted in the against-the-rule orientation after epithelial debridement. There were no significant changes in any corneal higher-order aberration parameter after epithelial debridement (p > 0.05).

CONCLUSIONS

In eyes with keratoconus, epithelial debridement increased the magnitude of anterior corneal prolateness and tended to increase astigmatism and shift its axis toward the against-the-rule orientation. This study supports the notion that the corneal epithelium smooths underlying Bowman layer irregularity in keratoconus.

Ultrahigh-resolution anterior segment optical coherence tomography for analysis of corneal microarchitecture during wound healing

PURPOSE

To employ ultrahigh-resolution (UHR) optical coherence tomography (OCT) for investigation of the early wound healing process in corneal epithelium.

METHODS

A custom-built UHR-OCT system assessed epithelial healing in human keratoconic cornea after epi-off crosslinking (CXL) procedure and a wound healing model in rabbits with iatrogenic corneal injury. 3D OCT data sets enhanced obtaining epithelial thickness maps and evaluation of reepithelization stage. Accompanying changes in deeper corneal microarchitecture were analysed.

RESULTS

The mean central corneal thickness in 40 eyes with keratoconus at baseline was 482.7 ± 38.2 μm, while mean central epithelial thickness (CET) was 43.8 ± 6.4 μm. At the final visit 20 ± 5 days post-CXL procedure, CET was 35.0 ± 5.8 μm, significantly thinner after reepithelization (p < 0.001). Surgical success was assessed at the final visit through the demarcation line (DL), identified at 43.7 ± 13.5% stromal depth. In rabbits, the mean CET in 20 eyes at baseline was 35.9 ± 2.6 μm. In rabbits that revealed complete wound closure (10/20 eyes) at the last study day at 72 hr, CET was significantly thinner compared to baseline (30.4 ± 2.8 μm versus 35.4 ± 2.9 μm, p = 0.005). An intra-stromal landmark indicating early keratocyte apoptosis was measured at 30.0 ± 5.1% stromal depth. Epithelial thickness maps showed the time-course of corneal healing.

CONCLUSION

Ultrahigh-resolution (UHR)-OCT provided precise assessment of epithelial wound and its healing by 3D-mapping. In addition, microarchitectural changes in the cornea in early phases of epithelial healing were revealed.

Distinguishing between contact lens warpage and ectasia: Usefulness of optical coherence tomography epithelial thickness mapping

PURPOSE

To distinguish between corneal ectasia and contact lens-related warpage by characteristic patterns on corneal topography and optical coherence tomography (OCT) epithelial thickness maps.

SETTING

Casey Eye Institute, Portland, Oregon, USA.

DESIGN

Prospective and retrospective case series.

METHODS

Axial and mean power maps were obtained on corneal topography systems. Epithelial thickness maps were generated using RTVue OCT. A sector divider was applied to all maps. The locations of the minimum epithelial thickness, maximum epithelial thickness, maximum axial power, and maximum mean power were determined based on sector averages. Agreement was defined as the extremums occurring in the same or adjacent sectors.

RESULTS

Twenty-one eyes with keratoconus, 6 eyes with forme fruste keratoconus (better eye of asymmetric keratoconus), and 15 eyes with contact lens-related warpage were identified. The keratoconus and forme fruste keratoconus eyes had coincident topographic steepening with epithelial thinning. The locations of minimum epithelial thickness and maximum axial power agreed in 90% of the keratoconic eyes, while the minimum epithelial thickness and maximum mean power agreed in 95% of them. Conversely, the warpage eyes had coincident topographic steepening with epithelial thickening and normal pachymetry maps. The locations of maximum epithelial thickness and maximum axial power agreed in 93% of the warpage eyes, while the maximum epithelial thickness and maximum mean power agreed in all warpage eyes.

CONCLUSION

Results show that epithelial thickness maps and corneal topographic maps are powerful synergistic tools in evaluating eyes with abnormal topography and can help differentiate between keratoconus and nonectatic conditions.

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

PURPOSE

To evaluate corneal epithelial thickness (CET) and corneal thickness (CT) in healthy eyes using spectral domain optical coherence tomography.

METHODS

Thirty-six healthy eyes were imaged using the Cirrus high-definition (HD)-optical coherence tomography device. The average CET and CT were assessed using Cirrus Review Software within predefined concentric corneal ring-shaped zones. Specific regions of CET (superior, inferior, temporal, nasal, superonasal, inferotemporal, superotemporal, and inferonasal) were also assessed. The difference between zones was compared between males and females.

RESULTS

The average CET was 48.3, 47.1, 46.1, and 45.8 μm in the 4 concentric zones (0-2, 2-5, 5-7, and 7-9 mm), respectively (P < 0.001). The average CT was 533.5, 550.8, and 579.4 μm in the 3 zones (0-2, 2-5, and 5-7 mm), respectively (P < 0.001). There was no statistically significant correlation between CET and CT in any of the measured zones. Males had thicker corneas than did females in each of the 3 CT zones (P < 0.05), but CET did not differ significantly. The CET superonasal-inferotemporal in 2.0 to 5.0 mm and CET superotemporal-inferonasal in 5.0- to 7.0-mm zones were significantly thinner in males than in females (-1.15 vs. 0.9 μm, -3.5 vs. -1.9 μm), respectively (P < 0.05).

CONCLUSIONS

Optical coherence tomography-based analysis of CET reveals that it is thinner in the periphery, whereas the total corneal thickness is greater. Although total CT seems to be influenced by sex, CET is not. Regional and sex-based variations in CT may need to be considered when assessing corneal and epithelial alterations in the setting of disease.

Corneal Epithelial Remodeling After Standard Epithelium-off Corneal Cross-linking in Keratoconic Eyes

PURPOSE

To evaluate remodeling of the corneal epithelium after epithelium-off corneal cross-linking (CXL).

METHODS

In this prospective single-center study, 93 eyes of 93 patients with progressive keratoconus underwent standard CXL. The maximum keratometry was assessed before and after CXL with Scheimpflug imaging, and the epithelial thickness profile across the central 5 mm of the cornea was assessed with spectral-domain optical coherence tomography anterior segment imaging.

RESULTS

The mean patient age was 27 ± 11 years; 76 patients (81%) were male and 17 (19%) were female. Between baseline and 6 months after CXL, the mean corneal maximum keratometry flattened from 58.90 to 57.80 diopters (P < .0001). The mean minimum epithelial thickness increased slightly (from 41 ± 6 to 42 ± 7 μm, P = .12), whereas the mean maximum epithelial thickness decreased slightly (from 65 ± 6 to 64 ± 7 μm, P = .067), reducing the net difference between the minimum and maximum epithelial thickness (from 24 ± 9 to 22 ± 9 μm, P = .0023). The difference between the minimum and maximum epithelial thickness was strongly positively correlated with the maximum keratometry reading at baseline (R² = 0.38) and at 6 months after CXL (R² = 0.59).

CONCLUSIONS

Epithelium-off CXL resulted in modest regularization of the epithelial thickness profile across the central 5 mm of the cornea at 6 months. This could slightly mask flattening of the underlying stroma. [J Refract Surg. 2018;34(6):408-412.].

Cornea and anterior eye assessment with slit lamp biomicroscopy, specular microscopy, confocal microscopy, and ultrasound biomicroscopy

Current corneal assessment technologies make the process of corneal evaluation extremely fast and simple, and several devices and technologies show signs that help in identification of different diseases thereby, helping in diagnosis, management, and follow-up of patients. The purpose of this review is to present and update readers on the evaluation of cornea and ocular surface. This first part reviews a description of slit lamp biomicroscopy (SLB), endothelial specular microscopy, confocal microscopy, and ultrasound biomicroscopy examination techniques and the second part describes the corneal topography and tomography, providing up-to-date information on the clinical recommendations of these techniques in eye care practice. Although the SLB is a traditional technique, it is of paramount importance in clinical diagnosis and compulsory when an eye test is conducted in primary or specialist eye care practice. Different techniques allow the early diagnosis of many diseases, especially when clinical signs have not yet become apparent and visible with SLB. These techniques also allow for patient follow-up in several clinical conditions or diseases, facilitating clinical decisions and improving knowledge regarding the corneal anatomy.

Distinguishing Keratoconic Eyes and Healthy Eyes Using Ultrahigh-Resolution Optical Coherence Tomography-Based Corneal Epithelium Thickness Mapping

PURPOSE

To find differences in epithelial thickness (ET) maps of eyes with keratoconus (KC) and healthy eyes.

DESIGN

Institutional cross-sectional study.

METHODS

In this study 40 keratoconic eyes and 76 healthy eyes were scanned using a custom-built ultrahigh-resolution optical coherence tomography system. Automated segmentation ET maps with 17 subsectors were calculated (central, temporal inferior, temporal superior, nasal inferior, and nasal superior area). The thinnest point of the epithelium (minET), the thickest point of the epithelium (maxET), and the thinnest point diagonally opposing the thickest point (ET_max/op) were additional parameters. Ratios were calculated as follows: minET/diagonally opposing point (R₁), maxET/diagonally opposing point (R₂), inferior temporal area/superior nasal area (R_TI/NS), and inferior/superior hemisphere (R_I/S). Furthermore, collected parameters were analyzed regarding their diagnostic accuracy (area under the curve; AUC).

RESULTS

Statistically significant differences were as follows: central ET, 46.25 ± 2.56/50.91 ± 1.66; minET, 38.50 ± 2.10/46.79 ± 1.27; ET_max/op, 47.14 ± 2.45/49.60 ± 1.57; temporal inferior area: 43.93 ± 2.95/51.04 ± 1.51 (all mean ± standard deviation, μm); R₁, 0.76 ± 0.09/0.93 ± 0.04; R₂, 1.08 ± 0.04/1.21 ± 0.16; R_TI/NS, 0.85 ± 0.08/1.02 ± 0.04; R_I/S: 0.92 ± 0.07/0.99 ± 0.02. AUC values were R₁: 0.979 (confidence interval [CI]: 0.957-1.000), R_TI/NS: 0.977 (CI: 0.951-1.000), and minET: 0.928 (CI: 0.880-0.977).

CONCLUSIONS

Epithelial thickness maps could clearly visualize different ET patterns. Parameters with the highest potential of diagnostic discrimination between eyes with KC and healthy eyes were, in descending order, R₁, R_TI/NS, and minET. Consequently, epithelial thickness irregularity and asymmetry seem to be the most promising diagnostic factor in terms of discriminating between keratoconic eyes and healthy eyes.

Temporal and Spatial Flap Variability in Laser In-Situ Keratomileusis by Optical Coherence Tomography

Purpose:

To study changes in flap thickness made with two different microkeratome heads across different corneal locations using anterior segment optical coherence tomography (OCT).

Methods:

In this prospective, non-randomized, consecutive case series, subjects who had their laser in-situ keratomileusis (LASIK) flaps made using 90 μm (MSU90) or 130 μm (MSU130) disposable M2 microkeratome heads were examined using OCT. The measurements were performed at three locations (central and 2.5 mm to either side) at 1 day, 1 week, and 1 month postoperatively.

Results:

The central flap thickness was 123 ± 15, 130 ± 14, and 127 ± 13 μm, respectively, at 1 day, 1 week, and 1 month postoperatively in the MSU90 group (41 eyes) and 142 ± 20, 147 ± 19, and 143 ± 15 μm, respectively, in the MSU130 group (47 eyes). At 1 month, peripheral flap thickness was 161 ± 17 and 159 ± 13 μm, respectively, at 2.5 mm to the right and left of corneal center in the MSU90 group. The corresponding figures were 170 ± 14 and 167 ± 13 μm, respectively, in the MSU130 group. There was a statistically significant difference between the two groups at all locations (P < 0.001). No statistically significant change in flap thickness was detected in either group at any assessment time. There was a partial positive correlation (after controlling for preoperative manifest refractive spherical equivalent) between central flap thickness and preoperative ultrasound central pachymetry (r = 0.739, P = 0.036) in the MSU90 group but not in the MSU130 group.

Conclusion:

Using OCT, changes in flap thickness were minimal in the first month after LASIK. Flap thickness correlated strongly with central corneal thickness if a 90 μm head was used.

Age- and sex-related differences in corneal epithelial thickness measured with spectral domain anterior segment optical coherence tomography among Egyptians

Is to measure the corneal epithelial thickness (CET) in a group of healthy Egyptian population and to investigate its variation with age and sex using spectral domain-anterior segment optical coherence tomography (SD-AS-OCT).This cross-sectional observational study includes 240 eyes of 120 healthy individuals (60 men, 60 women). Each gender was divided into 4 equal groups according to age as follows (18-29 years), (30-44 years), (45-59 years), and (60-80 years). The CET in 17 points over a corneal diameter of 6.0 mm was measured in each subject by SD-AS-OCT. The regional thickness changes were compared in different age groups of each gender separately and the correlations between the CET, age, and gender were analyzed.The CET of the central cornea (2 mm), the paracentral and the midperipheral zones (2-5 and 5-6 mm, respectively) of all males and females groups demonstrates highly significant changes with age (P < .001) with no significant difference between males and females. The measured parameters in the 2 age groups below 45 and above 45 years old revealed statistically significant difference with lower values in the elderly group (P < .001).The CET became thinner with age in the central, paracentral, and midperipheral zones in both genders and there is no difference between males and females. These findings could be valuable in refractive surgeries especially in age over 45.

Epithelial Thickness Profile Change After Combined Topography-Guided Transepithelial Photorefractive Keratectomy and Corneal Cross-linking in Treatment of Keratoconus

PURPOSE

To evaluate corneal epithelial remodeling after topography-guided transepithelial photorefractive keratectomy (PRK) combined with corneal collagen cross-linking (CXL) in the treatment of keratoconus.

METHODS

Retrospective analysis of the epithelial thickness distribution changes in 53 keratoconic eyes of 44 patients. Manifest refraction, maximum (Kmax) and minimum (Kmin) keratometry obtained by Placido topography, corneal irregularity index (IRI) measured by Scheimpflug topography, and the epithelial thickness profile over the central 5-mm zone obtained by anterior-segment spectral domain optical coherence tomography (SD-OCT) were evaluated preoperatively and at 1 to 3, 3 to 6, and more than 6 months postoperatively.

RESULTS

Preoperatively, the epithelial thickness at the thinnest area (MinArea) was 48.8 ± 4.4 µm, correlating negatively with Kmax (r = -0.310, P < .05) and IRI (r = -0.362, P < .05). At more than 6 months postoperatively, epithelial thickening of 5.5 ± 5.1 µm occurred at the thinnest area (MinArea). There was no significant change in the epithelial thickness in other areas, resulting in a decrease of difference in epithelial thickness between MinArea and the rest of the paracentral areas of 5.5 ± 4.3 µm. Corrected distance visual acuity, refractive astigmatism, Kmax, Kmin, and IRI all improved after the treatment (P < .05).

CONCLUSIONS

A significant epithelial thickness profile change occurred after the treatment due to an increase in thickness at the preoperatively thinnest area. Because the thickness in other areas remained largely unchanged, the treatment resulted in a more even epithelial thickness distribution. This may be attributed to regularized postoperative corneal stromal shape. [J Refract Surg. 2016;32(9):626-634.].

Differentiating Keratoconus and Corneal Warpage by Analyzing Focal Change Patterns in Corneal Topography, Pachymetry, and Epithelial Thickness Maps

Purpose

To differentiate between keratoconus and contact lens-related corneal warpage by combining focal change patterns in anterior corneal topography, pachymetry, and epithelial thickness maps.

Methods

Pachymetry and epithelial thickness maps of normal, keratoconus, and warpage, and forme fruste keratoconus (FFK) eyes were obtained from a Fourier-domain optical coherence tomography (OCT). Epithelial pattern standard deviation (PSD) was calculated and combined with two novel indices, the Warpage Index and the Anterior Ectasia Index, to differentiate between normal, keratoconus, and warpage eyes. The values of the three parameters were compared between groups.

Results

The study included 22 normal, 31 keratoconic, 11 warpage, and 8 FFK eyes. The epithelial PSD was normal (< 0.041) for 100% normal eyes and abnormal (> 0.041) for 100% of keratoconic eyes, 81.8% of warpage eyes, and 87.5% of FFK eyes. The Anterior Ectasia Index of normal eyes (1.66 ± 0.74) was significantly lower than that for the keratoconus eyes (17.5 ± 7.17), the warpage eyes (2.98 ± 1.69), and the FFK eyes (6.95 ± 5.86). The Warpage Index was positive in all warpage eyes and negative for all keratoconic and FFK eyes except three wearing rigid gas-permeable contact lens.

Conclusions

The epithelial PSD can distinguish normal from keratoconus or warpage, but does not distinguish between these two conditions. The Anterior Ectasia Index is abnormal in keratoconus but not warpage. The Warpage Index is positive for warpage and negative for keratoconus, except in cases where keratoconus and warpage coexist. Together, the three parameters are strong tripartite discriminators of normal, keratoconus, and warpage.

Detailed Distribution of Corneal Epithelial Thickness and Correlated Characteristics Measured with SD-OCT in Myopic Eyes

Purpose

To investigate the detailed distribution of corneal epithelial thickness in single sectors and its correlated characteristics in myopic eyes.

Methods

SD-OCT was used to measure the corneal epithelial thickness distribution profile. Differences of corneal epithelial thickness between different parameters and some correlations of characteristics were calculated.

Results

The thickest and thinnest part of epithelium were found at the nasal-inferior sector (P < 0.05) and at the superior side (P < 0.05). respectively. Subjects in the low and moderate myopia groups have thicker epithelial thickness than those in the high myopia group (P < 0.05). Epithelial thickness was 1.39 μm thicker in male subjects than in female subjects (P < 0.001). There was a slight negative correlation between corneal epithelial thickness and age (r = −0.13, P = 0.042). Weak positive correlations were found between corneal epithelial thickness and corneal thickness (r = 0.148, P = 0.031). No correlations were found between corneal epithelial thickness, astigmatism axis, corneal front curvature, and IOP.

Conclusions

The epithelial thickness is not evenly distributed across the cornea. The thickest location of the corneal epithelium is at the nasal-inferior sector. People with high myopia tend to have thinner corneal epithelium than low–moderate myopic patients. The corneal epithelial thickness is likely to be affected by some parameters, such as age, gender, and corneal thickness.

A protocol for topographic-guided corneal repair utilizing the US Food and Drug Administration-approved Wavelight Contoura

Purpose

To demonstrate how Wavelight Contoura can be used to repair corneas damaged by trauma and prior poor surgical outcomes.

Methods

Four representative eyes are presented that show different scenarios in which highly irregular corneas can be corrected with Wavelight Contoura using a protocol (named the San Diego Protocol) designed to use the information in Contoura processing. Both laser-assisted in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK) were used.

Results

Highly aberrant corneas with large amounts of warpage can be corrected safely with the Wavelight Contoura system. The San Diego Protocol requires individual analysis of each case with decisions based on the level of warpage and the level of epithelial hyperplastic compensation. The need for a second refractive power equalization procedure should be planned for.

Conclusion

Contoura measured refraction can be integrally used as part of the San Diego Protocol to safely repair highly warped corneas. The refractive outcomes show dramatic improvement in vision, best-corrected visual acuity (BCVA), refraction, and topographic uniformity.

Subclinical keratoconus detection by pattern analysis of corneal and epithelial thickness maps with optical coherence tomography

PURPOSE

To screen for subclinical keratoconus by analyzing corneal, epithelial, and stromal thickness map patterns with Fourier-domain optical coherence tomography (OCT).

SETTING

Four centers in the United States.

DESIGN

Cross-sectional observational study.

METHODS

Eyes of normal subjects, subclinical keratoconus eyes, and the topographically normal eye of a unilateral keratoconus patient were studied. Corneas were scanned using a 26,000 Hz Fourier-domain OCT system (RTVue). Normal subjects were divided into training and evaluation groups. Corneal, epithelial, and stromal thickness maps and derived diagnostic indices, including pattern standard deviation (PSD) variables and pachymetric map-based keratoconus risk scores, were calculated from the OCT data. Area under the receiver operating characteristic curve (AUC) analysis was used to evaluate the diagnostic accuracy of the indices.

RESULTS

The study comprised 150 eyes of 83 normal subjects, 50 subclinical keratoconus eyes of 32 patients, and 1 topographically normal eye of a unilateral keratoconus patient. Subclinical keratoconus was characterized by inferotemporal thinning of the cornea, epithelium, and stroma. The PSD values for corneal (P < .001), epithelial (P < .001), and stromal (P = .049) thickness maps were all significantly higher in subclinical keratoconic eyes than in the normal group. The diagnostic accuracy was significantly higher for PSD variables (pachymetric PSD, AUC = 0.941; epithelial PSD, AUC = 0.985; stromal PSD, AUC = 0.924) than for the pachymetric map-based keratoconus risk score (AUC = 0.735).

CONCLUSIONS

High-resolution Fourier-domain OCT could map corneal, epithelial, and stromal thicknesses. Corneal and sublayer thickness changes in subclinical keratoconus could be detected with high accuracy using PSD variables. These new diagnostic variables might be useful in the detection of early keratoconus.

FINANCIAL DISCLOSURES

Oregon Health and Science University (OHSU) and Drs. Li, Tan, and Huang have a significant financial interest in Optovue, Inc. These potential conflicts have been reviewed and managed by OHSU. Dr. Brass receives research grants from Optovue, Inc. Drs. Chamberlain and Weiss have no financial or proprietary interest in any material or method mentioned.

Corneal Epithelium Thickness Profile in 614 Normal Chinese Children Aged 7-15 Years Old

The purpose of the study is to describe the values and distribution of corneal epithelium thickness (CET) in normal Chinese school-aged children, and to explore associated factors with CET. CET maps were measured by Fourier-domain optical coherence tomography (FD-OCT) in normal Chinese children aged 7 to 15 years old from two randomly selected schools in Shanghai, China. Children with normal intraocular pressure were further examined for cycloplegic autorefraction, corneal curvature radius (CCR) and axial length. Central (2-mm diameter area), para-central (2- to 5-mm diameter area), and peripheral (5- to 6-mm diameter area) CET in the superior, superotemporal, temporal, inferotemporal, inferior, inferonasal, nasal, superonasal cornea; minimum, maximum, range, and standard deviation of CET within the 5-mm diameter area were recorded. The CET was thinner in the superior than in the inferior and was thinner in the temporal than in the nasal. The maximum CET was located in the inferior zone, and the minimum CET was in the superior zone. A thicker central CET was associated with male gender (p = 0.009) and older age (p = 0.037) but not with CCR (p = 0.061), axial length (p = 0.253), or refraction (p = 0.351) in the multiple regression analyses. CCR, age, and gender were correlated with para-central and peripheral CET.

In pursuit of objective dry eye screening clinical techniques

Dry eye is a multifactorial, progressive, and chronic disease of the tears and ocular surface. The disease is multi-factorial and has intermittent symptoms. Discomfort, visual disturbance, tear film instability with potential damage to the ocular surface, and increased tear film osmolarity are known associates.

Dry eye is a common clinical problem for eye-care providers worldwide and there is a large number of clinical investigative techniques for the evaluation of dry eye. Despite this, however, there is no globally accepted guideline for dry eye diagnosis and none of the available tests may hold the title of the ‘gold standard’. The majority of the techniques involved in the diagnosis of the disease, particularly for its early stages, has a large degree of subjectivity.

The purpose of this article is to review existing dry eye investigative techniques and to present a new objective dry eye screening technique based on optical coherence tomography.

Evaluation of Total Corneal Thickness and Corneal Layers With Spectral-Domain Optical Coherence Tomography

PURPOSE:

To evaluate total corneal thickness and corneal layers in healthy young adults using spectral-domain optical coherence tomography and to describe its repeatability and reproducibility.

METHODS:

Eighty-six eyes from 86 healthy volunteers were prospectively and consecutively enrolled. Manual measurements of central corneal thickness (CCT) and central thickness of epithelium, Bowman's layer, stroma, and the Descemet–endothelium complex were performed using Spectralis OCT (Heidelberg Engineering, Heidelberg, Germany). To assess the reliability of the repeated measurements, intraclass correlation coefficients and coefficients of variation were used.

RESULTS:

Mean CCT, epithelium, Bowman's layer, stroma, and Descemet–endothelium values were 555.50 ± 29.64, 54.60 ± 4.25, 16.70 ± 1.73, 467.51 ± 28.91, and 16.74 ± 1.66 µ m, respectively. The intraclass correlation coefficients ranged from 0.746 (Bowman's layer) to 0.999 (CCT and stroma) and from 0.483 (Bowman's layer) to 0.995 (CCT) and 0.998 (stroma) for intraobserver repeatability and interobserver reproducibility, respectively. The measurements showed coefficients of variation lower than 11% in all cases.

CONCLUSIONS:

This study establishes a normal database for corneal thickness and all its layers in healthy young adults with spectral-domain optical coherence tomography. This device exhibited a high degree of intraobserver repeatability and interobserver reproducibility for all regions except Bowman's layer.

[ J Refract Surg. 2016;32(1):27–32.]

Comparison of Corneal Epithelial Thickness Measurement Between Fourier-Domain OCT and Very High-Frequency Digital Ultrasound

PURPOSE

To compare measurements of corneal epithelial thickness using optical coherence tomography (OCT) and very high-frequency digital ultrasound (VHFDU).

METHODS

Retrospective analysis of 189 virgin corneas and 175 post-laser refractive surgery (LRS) corneas that had corneal epithelial thickness measurement with RTVue Fourier-domain OCT (Optovue, Inc., Fremont, CA) (tear film included) and Artemis VHFDU (ArcScan Inc., Morrison, CO) (tear film excluded). Averages were calculated for the central 2-mm diameter zone and for two further concentric annuli of 1.5- and 0.5-mm width, each divided into eight sectors. Agreement was analyzed by mean difference (OCT - VHFDU), 95% limits of agreement (LoA) (1.96 standard deviation of the difference), and Bland-Altman analysis.

RESULTS

In virgin epithelium, mean central thickness was 53.4 ± 3.20 µm (range: 46 to 62 µm) with OCT and 54.1 ± 2.96 µm (range: 48 to 61 µm) with VHFDU; OCT measured thinnest in 70% with a mean difference of -0.71 µm (95% LoA of ± 3.94 µm, P < .001). In post-LRS epithelium, mean central thickness was 57.9 ± 6.08 µm (range: 42 to 77 µm) with OCT and 60.5 ± 6.47 µm (range: 42 to 79 µm) with VHFDU; OCT measured thinnest in 88%, with a mean difference of -2.48 µm (95% LoA of ± 5.33 µm, P < .001). A larger difference between methods was more common with thicker epithelium.

CONCLUSIONS

Corneal epithelial thickness measurements using OCT were found to be slightly thinner than for VHFDU. In contrast to VHFDU, OCT measurement includes the tear film, so the true difference is probably approximately 4 µm more than reported. The difference was greatest inferiorly and higher for post-LRS eyes and in thicker epithelium.