Pachymetry Maps Research Articles

Identification of Keratoconus-Related Phenotypes in Three Ppip5k2 Mouse Models.

It is necessary to establish a mouse model of keratoconus (KC) for research and therapy. We aimed to determine corneal phenotypes in 3 Ppip5k2 mouse models. Central corneal thickness (CCT) was determined using spectral domain optical coherence tomography (SD-OCT) in Ppip5k2+/K^ (n = 41 eyes), Ppip5k2K^/K^ (n = 17 eyes) and 2 knock-in mice, Ppip5k2S419A/+ (n = 54 eyes) and Ppip5k2S419A/S419A (n = 18 eyes), and Ppip5k2D843S/+ (n = 42 eyes) and Ppip5k2D843S/D843S (n = 44 eyes) at 3 and 6 months. Pachymetry maps were generated using the Mouse Corneal Analysis Program (MCAP) to process OCT images. Slit lamp biomicroscopy was used to determine any corneal abnormalities, and, last, hematoxylin and eosin (H&E) staining using corneal sections from these animals was used to examine morphological changes. CCT significantly decreased from 3 to 6 months in the Ppip5k2+/K^ and Ppip5k2K^/K^ mice compared to their littermate controls. OCT-based pachymetry maps revealed abnormally localized thinning in all three models compared to their wild-type (WT) controls. Slit lamp examinations revealed corneal abnormalities in the form of bullous keratopathy, stromal edema, stromal scarring, deep corneal neovascularization, and opacities in the heterozygous/homozygous mice of the three models in comparison with their controls. Corneal histological abnormalities, such as epithelial thickening and stromal layer damage, were observed in the heterozygous/homozygous mice of the three models in comparison with the WT controls. We have identified phenotypic and histological changes in the corneas of three mouse lines that could be relevant in the development of animal models of KC.

Comparative Analysis of Tomographic Indicators Forecasting Decompensation in Fuchs Endothelial Corneal Dystrophy.

To compare the performance of 3 commercially available tomographers (the Pentacam Scheimpflug camera, the swept-source optical coherence tomography Casia, and the blue light slit-scanning tomographer Precisio) in the identification of patterns associated with Fuchs endothelial corneal dystrophy (FECD) decompensation. This was a clinic-based cross-sectional imaging study. Pachymetry maps and posterior surface elevation maps were acquired with the 3 devices from 61 eyes affected by FECD. The maps were graded according to the evidence of tomographic patterns predictive of FECD decompensation (loss of parallel isopachs, displacement of the thinnest point, and focal posterior depression) by 2 blind cornea specialists. The loss of parallel isopachs was significantly less frequently evident in Pentacam pachymetry maps [8%, 95% confidence interval (CI) (3%, 18%)] compared with both the Casia [31%, 95% CI (20%, 44%), P = 0.01] and Precisio devices [24%, 95% CI (15%, 37%), P = 0.05]. The displacement of the thinnest point was graded as most evident in a significantly higher proportion of Precisio pachymetry maps [43%, 95% CI (31%, 55%)] compared with both the Pentacam [13%, 95% CI (6%, 24%), P = 0.001] and Casia devices [21%, 95% CI (12%, 33%), P = 0.03]. There were no significant differences in the identification of focal posterior depression on posterior elevation maps across the 3 devices. Identification of patterns predictive of FECD prognosis on pachymetry and posterior elevation maps is possible with different devices. However, their evidence varies across tomographers, and the results from different devices are not interchangeable.

Diagnostic Importance of OCT Pachymetry in Keratoconus.

To demonstrate changes in distance and near fusional vergence measured with prism bars, while compensating for present heterophoria using current ametropia correction. In addition, to determine the differences in values of the AC/A ratio determined by the heterophoric (calculation) and gradient methods. The basic sample includes 19 subjects with a mean age of 21.5 ±3.0 years (min. 18, max. 27). We used the Von Graefe technique for examination of distance and near phoria, and prism bars for examination of fusion vergences measured in prism diopters. We divided the basic cohort into six research sets according to the size of distance and near heterophoria. This was a cohort of patients with distance (D OR) and near orthophoria (N OR), a cohort of patients with distance (D EX) and near exophoria (N EX) and a set of patients with distance (D ES) and near esophoria (N ES). In the case of both groups with exophoria (distance, near) we found a statistically significant result only for negative fusion vergence (NFV). There was a statistically significant increase in NFV in the sample with distance and near exophoria (D EX, p = 0.01 and B EX, p = 0.02, respectively). In our study, we also demonstrated a statistically significant difference (p < 0.001) in the values of the AC/A ratio measured by the gradient and heterophoric methods. The values determined by the gradient method are lower (3.0 ±1.1 pD/D versus 5.8 ±0.9 pD/D) than by the heterophoric method. By comparing fusion vergence values in patients with exophoria and orthophoria, we demonstrated that in the presence of distance or near exophoria there is an increase in ipsilateral fusion vergence. In the case of an increase in ipsilateral fusion vergence, the finding was statistically significant both distance and near (p = 0.01 and p = 0.02, respectively). By contrast, we were unable to prove this fact in the group of patients with esophoria. In our study, we also demonstrated a statistically significant difference (p < 0.001) in the values of the AC/A ratio measured by the gradient and heterophoric methods. The values determined by the gradient method are lower (3.0 ±1.1 pD/D versus 5.8 ±0.9 pD/D) than by the heterophoric method.

Scheimpflug Tomography as a Predictor of Corneal Edema After Phacoemulsification in Fuchs Endothelial Corneal Dystrophy.

To determine if Scheimpflug tomography pachymetry map and posterior elevation map patterns can predict the occurrence of corneal edema following uneventful phacoemulsification surgery in Fuchs endothelial corneal dystrophy (FECD). Observational prospective case-control study. Fifty FECD eyes (50 patients) with visually significant cataract: 25 with subclinical corneal edema (SCE) versus 25 without SCE. Preoperatively, FECD was clinically assessed, and only patients devoid of clinical corneal edema were enrolled. Utilizing the Mayo Clinic classification for subclinical corneal edema (SCE), eligible FECD eyes were stratified based on Scheimpflug imaging pachymetry map and posterior elevation map characteristics, including loss of regular isopachs, displacement of the cornea's thinnest point, and the presence of posterior surface depression, into two groups: Group A representing FECD with SCE, and Group B: FECD without SCE. One week postoperatively, clinical and tomographic evaluation was performed. Regression analysis was conducted to evaluate predictors of corneal edema after uneventful phacoemulsification surgery in both groups. All patients were successfully imaged before and 1 week after surgery. Visual acuity was significantly improved in both groups (P < 0.001). No postoperative clinical edema was observed in Group B, while 23 (92%) had mild edema and 2 (8%) had moderate edema in Group A. Both groups showed a significant increase in postoperative central corneal thickness (CCT) and thinnest corneal thickness (TCT) (both P < 0.001). Compared to Group B, Group A showed a significant central flattening of the anterior corneal surface (P = 0.007 and P = 0.04 for K1 and K2 respectively), and a significant increase in the postoperative posterior surface depression. Multivariate analysis showed that 94% of postoperative corneal edema could be predicted by the presence of preoperative posterior surface depression (P = 0.04, ARR = 5.8 (1.89-35.7)). Scheimpflug tomography pachymetry map and posterior elevation map patterns can predict corneal edema after uneventful phacoemulsification surgery in FECD with subclinical corneal edema.

Role of Fibroblast Growth Factor Receptor 2 (FGFR2) in Corneal Stromal Thinning.

To determine the role of fibroblast growth factor receptor 2 (FGFR2)-mediated signaling in keratocytes during corneal development, a keratocyte-specific FGFR2-knockout (named FGFR2cKO) mouse model was generated, and its phenotypic characteristics were determined. A FGFR2cKO mouse model was generated by the following method: FGFR2 flox mice were crossed with the inducible keratocyte specific-Cre mice (Kera-rtTA/tet-O-Cre). Both male and female FGFR2cKO- and control mice (1 to 3-months-old) were analyzed for changes in corneal topography and pachymetry maps using the optical coherence tomography (OCT) method. The comparative TUNEL assay and immunohistochemical analyses were performed using corneas of FGFR2cKO and control mice to determine apoptotic cells, and expression of collagen-1 and fibronectin. Transmission electron microscopic analysis was conducted to determine collagen structures and their diameters in corneas of FGFR2cKO and control mice. OCT-analyses of corneas of FGFR2cKO mice (n = 24) showed localized central thinning and an increased corneal steepness compared to control mice (n = 23). FGFR2cKO mice further showed a decreased expression in collagen-1, decreased collagen diameters, acute corneal hydrops, an increased fibronectin expression, and an increased number of TUNEL-positive cells suggesting altered collagen structures and keratocytes' apoptosis in the corneas of FGFR2cKO mice compared to control mice. The FGFR2cKO mice showed several corneal phenotypes (as described above in the results) that are also exhibited by the human keratoconus corneas. The results suggested that the FGFR2cKO mouse model serves to elucidate not only the yet unknown role of FGFR2-mediated signaling in corneal physiology but also serves as a model to determine molecular mechanism of human keratoconus development.

Corneal Stress Distribution Evolves from Thickness-Driven in Normal Corneas to Curvature-Driven with Progression in Keratoconus

To introduce the novel parameter of Corneal Contribution to Stress (CCS) and compare stress distribution patterns between keratoconus (KCN) and normal corneas. Prospective, observational, cross-sectional study. The study included 66 eyes of 40 subjects diagnosed with KCN and 155 left eyes from 155 normal control (NRL) subjects. Tomography was obtained to calculate the newly proposed CCS, defined according to the hoop stress formula without intraocular pressure, R/2t, where R is the radius of curvature and t is the thickness. CCS maps were calculated from pachymetry and tangential curvature maps. Custom software identified the 2-mm-diameter zones of greatest curvature (Cspot-max), thinnest pachymetry (Pach-min), greatest stress (CCSmax), and lowest stress (CCSmin). Stress difference (CCSdiff) was calculated as CCSmax - CCSmin. Distances between Cspot-max vs. Pach-min, vs. CCSmax, and vs. CCSmin, as well as between Pach-min vs. CCSmax and vs. CCSmin, were calculated. t tests were performed between cohorts, and paired t tests were performed within cohorts. Univariate linear regression analyses were performed between parameters and distances. The significance threshold was P < 0.05. Corneal stress parameters, corneal features of maximum curvature, minimum thickness, and distances between corneal stress parameters and corneal features. CCSmax was significantly closer to Pach-min (0.79 ± 0.92) and Cspot-max (2.04 ± 0.85) than CCSmin (3.17 ± 0.38, 2.73 ± 1.53, respectively) in NRL, P < 0.0001, whereas CCSmin was significantly closer to Cspot-max (1.35 ± 1.43) than CCSmax (2.52 ± 0.72) in KCN, P < 0.0001. Cspot-max (severity) was significantly related to CCSdiff in KCN (P < 0.0001; R2= 0.5882) with a weak relationship in NRL (P < 0.0080, R2= 0.0451). Cspot-max was significantly related to the distance from Pach-min to CCSmax (P < 0.0001; R2= 0.3737) without significance in NRL (P= 0.8011). Corneal stress is driven by thickness in NRL, with greatest stress at thinnest pachymetry and greatest curvature. However, maximum stress moves away from thinnest pachymetry with progression in KCN, and minimum stress is associated with maximum curvature. Severity in KCN is significantly related to greater difference between maximum and minimum stress, consistent with the biomechanical cycle of decompensation. Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Comparison between the CASIA SS-1000 and Pentacam in measuring corneal curvatures and corneal thickness maps

PurposeTo compare the intra-device repeatability and inter-device reproducibility between two anterior segment imaging instruments, the CASIA SS-1000 (Tomey Corp., Nagoya, Japan) and Pentacam (OCULUS, Arlington, WA) in measuring anterior segment parameters.MethodsSingle-center, prospective clinical trial. Participants ≥20 years of age were included. One eye was randomly selected, each imaged by three CASIA SS-1000 devices and three Pentacam devices by three different examiners. Each photographer operated a pair of devices, one CASIA SS-1000 and one Pentacam. The image order for each participant was determined by a random permutation table. Three images were taken from each device. A total of 18 images were taken for each eye. Ratios of the standard deviations, referenced as (CASIA/Pentacam), were calculated to compare the repeatability and reproducibility of the two imaging instruments.ResultsIn all, 66 participants with a mean age of 46.4 years (±21.7) were enrolled in the study. All repeatability ratios and intra-device variability were less than 1 (anterior corneal curvature: flat = 0.86, steep = 0.85; posterior corneal curvature: flat = 0.43, steep = 0.61; and map: thinnest = 0.22; central = 0.24, 2 mm = 0.26, 4 mm = 0.27, and 6 mm = 0.30). All reproducibility ratios, which measure the inter-device variability, were less than 1 (anterior corneal curvature: flat = 0.58, steep = 0.73; posterior corneal curvature: flat = 0.25, steep = 0.31; and pachymetry map: thinnest = 0.20; central = 0.20; 2 mm = 0.20; 4 mm = 0.19; and 6 mm = 0.22). A ratio of less than 1 indicates that the CASIA SS-1000 has more consistent measurements.ConclusionsThe CASIA SS-1000 was found to have better repeatability and reproducibility compared to the Pentacam for both corneal curvature and pachymetry maps. This greater consistency may require further study to determine whether the decreased variability can be translated into improved clinical results.

Role of epithelial mapping in the differentiation between early keratoconus and high regular astigmatism using spectral-domain optical coherence tomography

Pur6pose To detect epithelial thickness-based diagnostic variables to detect early keratoconus (KC) and differentiate cases of early KC from high regular astigmatism, especially if abnormal topographic changes are present. Patients and methods A total of 84 eyes with high regular astigmatism on Scheimpflug imaging were evaluated by anterior segment optical coherence tomography (AS-OCT). Imaging of the cornea as well as pachymetry and epithelial thickness mapping was done using AS-OCT via a special lens mounted to a tomographic device. The same was done using Scheimpflug imaging (CSO Sirius device). Thickness of the corneal epithelium was automatically mapped using a computer algorithm. Calculations of the following diagnostic factors were recorded: minimum, superior–inferior, minimum–maximum, root-mean-square variation, root-mean-square pattern deviation, and thickness of the zonal epithelium. Results This study analyzed 84 eyes divided into two groups: group A (n=56 eyes) had high regular astigmatism and group B (n=28 eyes) with early KC. The mean spherical refraction, cylindrical refraction, and central corneal thickness (Scheimpflug imaging) for group A were −1.16±1.02 D, −3.67±0.67, and 542.88±29.64 μm, respectively. In group A, the mean central corneal thickness and central epithelial thickness was 538.84±29.67 and 52.34±1.69 μm, respectively. The mean spherical refraction, cylindrical refraction, central corneal, and epithelial thickness mean for group B were −1.75±0.87, −4.02±0.69 D, 505.36±28.48, and 49.93±0.9 μm, respectively. A significant correlation between central epithelial thickness with anterior elevation was noted in group B (P=0.048). Conclusion AS-OCT epithelial mapping may prove to be a useful diagnostic tool for determining early development of KC.

Effect of conventional and orthokeratological hard contact lenses on anatomical and functional characteristics of the cornea

This study evaluated the potential effects of conventional hard contact lenses (HCL) and orthokeratological contact lenses (OKL) on anatomical and functional condition of the cornea in myopia correction. The study included 80 patients (159 eyes) with low, moderate and high myopia. Group 1 consisted of 40 patients (79 eyes) who used conventional HCL; group 2 included 40 patients (80 eyes) who used OKL. All patients underwent topographic keratometry, corneal pachymetry mapping (Pentacam, Oculus, Germany; Visante OCT, Carl Zeiss, Germany), high-order aberrometry (OPD Scan, Nidek, Japan), confocal microscopy (Confoscan 4, Nidek, Japan), evaluation of corneal biomechanical properties (ORA, Reichert Technologies, USA) and corneal light scattering (Pentacam, Oculus, Germany). Examinations were taken before the treatment started and after 8-12 months of contact lens wear. Group 1 showed corneal thickness increase in all zones (by 0.9-1.1%), no significant changes in corneal refraction, and increase in corneal hysteresis and corneal resistance factor. OKL wear led to a significant flattening of anterior surface of the cornea and steepening of its paracentral area, decrease in central corneal thickness (by 2.8%) and increase in mid-peripheral thickness (by 2.2%). No significant changes in posterior corneal surface were observed in the study patients. More significant increase in higher-order aberrations and the degree of light scattering was observed in group 2, while changes in subepithelial nerve plexus and stromal structure were more significant in group 1. Long-term OKL wear shows more significant morphological and functional corneal changes compared to RGP lens.

Determining the center of a keratoconus: Comparison of different tomographic parameters and impact of disease severity.

PurposeThere exists remarkable variation in definitions for the location of the center of a keratoconus. The objective of this study was to analyze deviations between locations obtained by different tomographic maps for that purpose. Furthermore, it was investigated whether these deviations are influenced by disease severity.MethodsIn 162 eyes with keratoconus, corneal tomographic maps derived by Scheimpflug technology were retrospectively analyzed to determine the cone location with 5 different methods: maximum axial curvature of the front surface (Kmax), maximum tangential curvature of the front surface (tKmax), minimum pachymetry (Pachymin), maximum elevation of the front surface (ELEF), and maximum elevation of the back surface (ELEB). Distances between the locations were calculated and tested for a correlation with keratoconus severity and distance between cone and corneal vertex.ResultsCone locations derived from the curvature maps (Kmax, tKmax) showed the lowest agreement with the locations determined by pachymetry or elevation maps. The largest distances were found between Kmax and Pachymin [Median and Interquartile range: 1.19 mm (0.87, 1.60)], Kmax and ELEB [1.12 mm (0.79, 1.41)], and Kmax and ELEF [0.97 mm (0.64, 1.27)]. Low distances (<0.5 mm) were calculated between ELEB and ELEF, and ELEB and Pachymin. All of the calculated distances between the locations showed a significant negative correlation with keratoconus severity and most of them increased significantly with a more peripheral position of the cone (p < 0.05).ConclusionsThere was low consistency between different methods for describing the location of a keratoconus. Curvature-based determinations of the cone center (Kmax, tKmax) showed the highest deviations and should not be used for that purpose. However, the discrepancies between different cone location methods diminished with increasing disease severity and more central position of the cone.

P-16 Predicting ablation spherical equivalent of prior LASIK treatment from corneal pachymetry map.

Pachymetry data were recovered retrospectively from patients who had previous LASIK for refractive purposes between 2019 and 2020. Patients with any corneal disorder were excluded. Ablation spherical equivalent was predicted from central to semi-peripheral corneal thickness (CPT) ratio, both for values provided by Pentacam, and values computed from extracted raw pachymetry data. Data were analysed for 140 eyes of 73 patients (42% female, mean age 40.9, SD 12.8). CPT-ratio cut-off for distinction between myopic and hyperopic LASIK was 0.86 for pentacam-provided values. Sensitivity and specificity were 0.7 and 0.95, respectively. Accuracy increased with computation of CPT ratio based on extracted raw data. Sensitivity and specificity were 0.87 and 0.99, respectively. There was a marked linear correlation between CPT-ratio and ablation spherical equivalent (R2=0.93). CPT ratio cut-offs can correctly classify hyperopic versus myopic spherical equivalent of previous LASIK ablation. This could prove useful for increased accuracy of intraocular lens (IOL) calculations for patients with no historical data of their prior LASIK surgery at the time of cataract surgery planning.

Predicting Corneal Improvement after Descemet Membrane Endothelial Keratoplasty for Fuchs Endothelial CornealDystrophy.

PurposeTo develop a model to predict corneal improvement after Descemet membrane endothelial keratoplasty (DMEK) for Fuchs endothelial corneal dystrophy (FECD) from Scheimpflug tomography.DesignCross-sectional study.ParticipantsForty-eight eyes (derivation group) and 45 eyes (validation group) with a range of severity of FECD undergoing DMEK.MethodsScheimpflug images were obtained before and after DMEK. Before DMEK, pachymetry map and posterior elevation map patterns were quantified by a special image analysis program measuring tomographic features of edema (loss of regular isopachs, displacement of the thinnest point of the cornea, posterior surface depression). Image-derived novel parameters were combined with instrument-derived parameters, and the relative influences of parameters associated with the change in central corneal thickness (CCT) after DMEK in the derivation group were determined by using a gradient boosting machine learning model. The parameters with highest relative influence were then fit in a linear regression model. The derived model was applied to the validation group. Correlations and agreement were assessed between predicted and observed changes in CCT.Main Outcome MeasuresPredictive power (R2) and mean difference between predicted and observed change in CCT.ResultsThe gradient boosting machine model identified 4 novel parameters of isopach circularity and eccentricity and 1 instrument-derived parameter (posterior surface radius); preoperative CCT was a poor predictor. In the derivation group, the model strongly predicted the change in CCT after DMEK (R2 = 0.80; 95% confidence interval [CI], 0.71–0.89) and the mean difference between predicted and observed change was, by definition, 0 μm. When the same 5 parameters were fit to the validation group, the model performed very highly (R2 = 0.89; 95% CI, 0.84–0.94). When the coefficient estimates from the derivation model were used to predict the change in CCT in the validation group, the predictive power was also high (R2 = 0.78; 95% CI, 0.68–0.88), and the mean difference was 4 μm (predicted minus observed).ConclusionsScheimpflug tomography maps of corneas with FECD can predict the improvement in CCT after DMEK, independent of preoperative corneal thickness measurement. The model could be applied in clinical practice or for clinical research of FECD.

Visual Function in Pseudophakic Eyes with Fuchs’ Endothelial Corneal Dystrophy

To assess vision in pseudophakic eyes with Fuchs' endothelial corneal dystrophy (FECD) before the onset of clinically detectable corneal edema. Cross-sectional study. Sixty-one otherwise healthy pseudophakic eyes of 38 subjects with FECD (without clinically detectable edema) and 17 otherwise healthy pseudophakic eyes of 9 subjects with normal corneas. Subjects underwent clinical examination to determine the morphologic distribution of guttae (severity grading). Standardized best-corrected high-contract and low-contrast (photopic and mesopic) visual acuity (HCVA, LCVA) and straylight were measured. Scheimpflug tomography posterior elevation and pachymetry maps were interpreted for 3 tomographic features of subclinical edema: loss of regular isopachs, displacement of the thinnest point of the cornea, and presence of posterior surface depression. In FECD without tomographic features of edema (ie, normal tomography patterns), HCVA, LCVA, and straylight did not differ from that of eyes with normal corneas (P ≥ .09); these eyes encompassed the full range of severity grading of guttae. In FECD with all 3 tomographic features of edema, the same parameters were worse compared with eyes with normal corneas (P ≤ .02). In FECD with 1 or 2 tomographic abnormalities, mesopic LCVA (P=.04) and straylight (P=.003) were worse compared with eyes with normal corneas. Impairment of vision was associated with the presence of tomographic edema in eyes with FECD. When tomography patterns were normal in FECD (ie, guttae were present without tomographic edema), visual acuity and straylight were normal, and therefore corneal surgical intervention would not typically be indicated to improve vision.

The Location Consistency Index Helps to Distinguish Eyes With Subclinical Keratoconus From Normal Eyes.

To develop a novel index that combines the locations and magnitudes of corneal alterations to improve discrimination of eyes with subclinical keratoconus from normal eyes. A Scheimpflug-based tomography system was used to image 252 eyes (normal: 78 eyes, subclinical keratoconus: 71 eyes, and keratoconus: 103 eyes) of 252 patients from two clinical centers. Coordinates and magnitudes of the maximum corneal protrusion alterations were extracted from curvature, elevation, and pachymetry maps. A location consistency index (LCI) was calculated from the Euclidean distances among these locations. A logistic regression model, named the location consistency enhanced score (LCES), which combined the LCI and the magnitudes of these maximum alterations, was trained and tested in two different datasets. The LCI in eyes with subclinical keratoconus was 7.8 ± 2.6 µm, which was significantly different from that in normal eyes (11.8 ± 3.9 µm) and eyes with keratoconus (5.8 ± 2.4 µm) (all P < .001). The LCI could differentiate eyes with subclinical keratoconus from normal eyes with a sensitivity of 67.6%, specificity of 83.3%, and area under the receiver operating characteristic curve (AUC) of 0.81. Combining the magnitudes of these maximum alterations with the LCI for the LCES yielded a sensitivity of 90.0% and a specificity of 74.4% for differentiating eyes with subclinical keratoconus from normal eyes (AUC: 0.91). The LCI can assist in differentiating eyes with subclinical keratoconus from normal eyes. The LCES is a potential new index to assist in a confirmatory test of eyes with subclinical keratoconus. [J Refract Surg. 2022;38(1):35-42.].

Pellucid marginal degeneration versus keratoconus: distinction with wide-field SD-OCT corneal sublayer pachymetry

PurposeTo evaluate the capability of wide-field spectral-domain optical coherence tomography (SD-OCT) corneal sublayer pachymetry to distinguish between keratoconus and pellucid marginal degeneration (PMD).MethodsThis prospective cross-sectional study included 69 eyes (59...

Diagnostic Accuracy of Anterior Segment Optical Coherence Tomography Pachymetry Mapping and Detection for Early Keratoconus using Corneal Topography as Gold Standard

Background: Optical coherence tomography (OCT) derived pachymetry mapping has potential in diagnosis of early and advancing keratoconus. The OCT corneal pachymetry map–based logistic regression formula and the keratoconus risk scoring system has been proven to provide very accurate results in keratoconus identification. In keratoconus screening these techniques might be helpful. Objectives: To ascertain the diagnostic accuracy of anterior segment optical coherence tomographic corneal pachymetry to diagnose the cases the cases of early keratoconus by using corneal topography as a high standard with which other techniques of these kinds are compared. Study Design: Cross-sectional (validation) study. Duration: One year from July 01, 2019 to June 30, 2020. Settings: Department of Ophthalmology, Allied Hospital/DHQ Hospital, Faisalabad Pakistan. Methodology: A total of 195 patients having asymmetrical astigmatism (&gt;1 diopter), 12-40 years of age of both genders were included. Patients with corneal ulcer and corneal opacity were excluded. After complete examination corneal topography and anterior segment optical coherence tomography was performed. Tomographic minimum central corneal thickness was recorded and assessed for cutoff value, if exceeding cutoff value patient was diagnosed with the early keratoconus. Results: In OCT pachymetry positive patients, 103 (True Positive) had early keratoconus and 05 (False Positive) had no early keratoconus on corneal topography. Among 87, OCT pachymetry negative patients, 04 (False Negative) had early keratoconus on corneal topography whereas 83 (True Negative) had no early keratoconus on corneal topography (p=0.0001). Overall sensitivity, specificity, positive predictive value, negative predictive value and diagnostic accuracy of anterior segment optical coherence tomographic corneal pachymetry to diagnose the cases of early keratoconus in the suspected individuals by using corneal topography as gold standard was 96.26%, 94.32%, 95.37%, 95.40% and 95.38% respectively. Conclusion: This study concluded that diagnostic accuracy of anterior segment optical coherence tomographic corneal pachymetry to find out the cases of early keratoconus is very high. Keywords: Optical coherence tomographic corneal pachymetry, Keratoconus, Sensitivity

Anterior segment-optical coherence tomography for evaluation of the epithelium thickness profile in keratoconic corneas and normal corneas

Purpose This study intends to compare the characteristic distributive epithelial pattern by Fourier-domain anterior segment-optical coherence tomography (AS-OCT) corneal mapping between keratoconic and normal eyes. Patients and methods This prospective case–control study included 51 participants who were divided into two groups: study group A (formed of 50 eyes of 26 keratoconic participants) and control group B (50 eyes of 25 healthy controls of matched age and sex with group A). Maps of corneal epithelial statistics within central 5 mm [S: 2–5 mm (superior), I: 2–5 mm (inferior), minimum, maximum, SD (topographic variability), minimum−maximum], and the total corneal pachymetry maps were assessed by the Fourier-domain AS-OCT system and imaged by Scheimpflug imaging corneal topography for both groups. Results For group A of keratoconic corneas, the attained results are as follows: the mean of epithelial thickness at the center was 50.1±7.98 µm, superior 56.01±6.98 µm, inferior 48.73±5.97 µm, minimum 39.95±9.11 µm, maximum 62.92±8.85 µm, minimum−maximum −22.01±10.91 µm, and topographic variability 6.9±4.2 µm. For group B of healthy control eyes, the mean of epithelial thickness at the center was 52.71±3.71 µm, superior 52.29±3.32 µm, inferior 53.42±3.11 µm, minimum 48.89±3.71 µm, maximum 55.92±3.47 µm, minimum−maximum −6.3±3.51 µm, and topographic variability 1.53±0.82 µm. All variables of epithelial thickness between the two groups are significant (P&lt;0.01). In comparing the epithelial map of keratoconus (KCN) with the control group, the epithelium was found to be thicker at the maximum (+7 µm) and superior location (+3.72 µm), but thinner at the minimum (−8.94 µm) and the inferior (−4.69 µm) with highly significant differences in both minimum−maximum (−15.71) and topographic variability (+5.37). Moreover, in KCN, the point of minimum epithelial thickness was in accordance with the minimum point of the total corneal thickness and the maximum point of back elevation. Conclusion The mapping for epithelial thickness utilizing AS-OCT could be a promising tool in KCN diagnosis.

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

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. 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. 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 6to 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. 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.

Prediction of keratoconus progression using deep learning of anterior segment optical coherence tomography maps.

BackgroundTo predict keratoconus progression using deep learning of the color-coded maps measured with a swept-source anterior segment optical coherence tomography (As-OCT) device.MethodsWe enrolled 218 keratoconic eyes with and without disease progression. Using deep learning of the 6 color-coded maps (anterior elevation, anterior curvature, posterior elevation, posterior curvature, total refractive power, and pachymetry map) obtained by the As-OCT (CASIA, Tomey), we assessed the accuracy, sensitivity, and specificity of prediction of keratoconus progression in such eyes.ResultsDeep learning of the 6 color-coded maps exhibited an accuracy of 0.794 in discriminating keratoconus with and without progression. For a single map analysis, posterior elevation map (0.798) showed the highest accuracy, followed by anterior curvature map (0.775), posterior corneal curvature map (0.757), anterior elevation map (0.752), total refractive power map (0.729), and pachymetry map (0.720), in distinguishing between progressive and non-progressive keratoconus. The use of the adjusted algorithm by age subgroups improved to an accuracy of 0.849.ConclusionsDeep learning of the As-OCT color-coded maps effectively discriminates progressive keratoconus from non-progressive keratoconus with an accuracy of approximately 85% using the adjusted age algorithm, indicating that it will become an aid for predicting the progression of the disease, which is clinically beneficial for decision-making of the surgical indication of corneal cross-linking (CXL).

Corneal pachymetry by AS-OCT after Descemet\u2019s membrane endothelial keratoplasty

Corneal thickness (pachymetry) maps can be used to monitor restoration of corneal endothelial function, for example after Descemet’s membrane endothelial keratoplasty (DMEK). Automated delineation of the corneal interfaces in anterior segment optical coherence tomography (AS-OCT) can be challenging for corneas that are irregularly shaped due to pathology, or as a consequence of surgery, leading to incorrect thickness measurements. In this research, deep learning is used to automatically delineate the corneal interfaces and measure corneal thickness with high accuracy in post-DMEK AS-OCT B-scans. Three different deep learning strategies were developed based on 960 B-scans from 50 patients. On an independent test set of 320 B-scans, corneal thickness could be measured with an error of 13.98 to 15.50 μm for the central 9 mm range, which is less than 3% of the average corneal thickness. The accurate thickness measurements were used to construct detailed pachymetry maps. Moreover, follow-up scans could be registered based on anatomical landmarks to obtain differential pachymetry maps. These maps may enable a more comprehensive understanding of the restoration of the endothelial function after DMEK, where thickness often varies throughout different regions of the cornea, and subsequently contribute to a standardized postoperative regime.