In-vivo Three-dimensional Characteristics of Bowman's Layer and Endothelium/Descemet's Complex Using Corneal Microlayer Tomography in Healthy Subjects

Purpose: To characterize the three-dimensional (3D) thickness profile and age-related changes of Bowman's layer (BL), and endothelium/Descemet's membrane (En/DM) complex among healthy individuals using Corneal Microlayer Tomography (CML-T), and to describe its repeatability and accuracy.Methods: Sixty-six eyes of 41 healthy volunteers; 27 eyes (< 40 years old), and 39 eyes (>40 years old) were imaged using HD-OCT. Automatic and manual segmentation of the corneal layers was performed, and 3D thickness maps were generated, using custom-built CML-T software. A regional analysis of mean thickness parameters between the 2 age groups was performed. A regression analysis was used to assess the correlation between age, and thickness maps. Intraclass Correlation Coefficients (ICC), Coefficients of Variation (COV), and Bland-Altman plots were used to assess the reliability of the repeated measurements in 198 locations.Results: CML-T successfully mapped the BL and En/DM in all included eyes. Thickness maps showed a significant increase in corneal thickness (CT), BL thickness (BMT), and En/DM complex thickness (DMT) toward the periphery with a mean difference 28 µm (p < .001), 1.1 µm (p < .001), and 1.4 µm (p < .001), respectively. There was a strong correlation between age and central DMT (r = 0.61; p < .001), while there was no correlation between age and both CT, and BMT. ICC values ranged from 0.9 (BMT) to 0.997 (DMT), and from 0.808 (BMT) to 0.979 (CT) for intraoperator repeatability of manual measurements, and the accuracy of auto matic measurements, respectively. COV values were lower than 7.5% in all cases.Conclusion: CML-T is a novel tool that can generate 3D-thickness maps of both BL and En/DM. CT, BMT, and DMT increase toward the periphery in healthy corneas. DMT increases with aging, while BMT does not. We also report excellent repeatability, accuracy and good agreement between automatic and manual measurements.

Diagnostic Performance of Three-Dimensional Endothelium/Descemet Membrane Complex Thickness Maps in Active Corneal Graft Rejection

PURPOSE

To evaluate the performance of 3-dimensional (3D) endothelium/Descemet membrane complex thickness (En/DMT) maps vs total corneal thickness (TCT) maps in the diagnosis of active corneal graft rejection.

DESIGN

Cross-sectional study.

METHODS

Eighty-one eyes (32 clear grafts and 17 with active rejection, along with 32 age-matched control eyes) were imaged using high-definition optical coherence tomography (HD-OCT), and a custom-built segmentation algorithm was used to generate 3D color-coded maps of TCT and En/DMT of the central 6-mm cornea. Regional En/DMT and TCT were analyzed and compared between the studied groups. Receiver operating characteristic curves were used to determine the accuracy of En/DMT and TCT maps in differentiating between studied groups. Main outcome measures were regional En/DMT and TCT.

RESULTS

Both regional TCT and En/DMT were significantly greater in actively rejecting grafts compared to both healthy corneas and clear grafts (P < .001). Using 3D thickness maps, central, paracentral, and peripheral En/DMT achieved 100% sensitivity and 100% specificity in diagnosing actively rejecting grafts (optimal cut-off value [OCV] of 19 μm, 24 μm, and 26 μm, respectively), vs only 82% sensitivity and 96% specificity for central TCT, OCV of 587 μm. Moreover, central, paracentral, and peripheral En/DMT correlated significantly with graft rejection severity (r = 0.972, r = 0.729, and r = 0.823, respectively; P < .001).

CONCLUSION

3D En/DMT maps can diagnose active corneal graft rejection with excellent accuracy, sensitivity, and specificity. Future longitudinal studies are required to evaluate the predictive and prognostic role of 3D En/DMT maps in corneal graft rejection.

Expansion of Peripheral Visual Field with Novel Virtual Reality Digital Spectacles

PURPOSE

To examine an image remapping method for peripheral visual field (VF) expansion with novel virtual reality digital spectacles (DSpecs) to improve visual awareness in glaucoma patients.

DESIGN

Prospective case series.

METHODS

Monocular peripheral VF defects were measured and defined with a head-mounted display diagnostic algorithm. The monocular VF was used to calculate remapping parameters with a customized algorithm to relocate and resize unseen peripheral targets within the remaining VF. The sequence of monocular VF was tested and customized image remapping was carried out in 23 patients with typical glaucomatous defects. Test images demonstrating roads and cars were used to determine increased awareness of peripheral hazards while wearing the DSpecs. Patients' scores in identifying and counting peripheral objects with the remapped images were the main outcome measurements.

RESULTS

The diagnostic monocular VF testing algorithm was comparable to standard automated perimetric determination of threshold sensitivity based on point-by-point assessment. Eighteen of 23 patients (78%) could identify safety hazards with the DSpecs that they could not previously. The ability to identify peripheral objects improved with the use of the DSpecs (P = 0.024, chi-square test). Quantification of the number of peripheral objects improved with the DSpecs (P = 0.0026, Wilcoxon rank sum test).

CONCLUSIONS

These novel spectacles may enhance peripheral objects awareness by enlarging the functional field of view in glaucoma patients.

Toward Improving the Mobility of Patients with Peripheral Visual Field Defects with Novel Digital Spectacles

PURPOSE

To assess the efficacy of novel Digital spectacles (DSpecs) to improve mobility of patients with peripheral visual field (VF) loss.

DESIGN

Prospective case series.

METHODS

Binocular VF defects were quantified with the DSpecs testing strategy. An algorithm was implemented that generated personalized visual augmentation profiles based on the measured VF. These profiles were achieved by relocating and resizing video signals to fit within the remaining VF in real time. Twenty patients with known binocular VF defects were tested using static test images, followed by dynamic walking simulations to determine if they could identify objects and avoid obstacles in an environment mimicking a real-life situation. The effect of the DSpecs were assessed for visual/hand coordination with object-grasping tests. Patients performed these tests with and without the DSpecs correction profile.

RESULTS

The diagnostic binocular VF testing with the DSpecs was comparable to the integrated monocular standard automated perimetry based on point-by-point assessment with a mismatch error of 7.0%. Eighteen of 20 patients (90%) could identify peripheral objects in test images with the DSpecs that they could not previously. Visual/hand coordination was successful for 17 patients (85%) from the first trial. The object-grasping performance improved to 100% by the third trial. Patient performance, judged by finding and identifying objects in the periphery in a simulated walking environment, was significantly better with the DSpecs (P = 0.02, Wilcoxon rank sum test).

CONCLUSIONS

DSpecs may improve mobility by facilitating the ability of patients to better identify moving peripheral hazardous objects.

Automatic Segmentation of Corneal Microlayers on Optical Coherence Tomography Images

Purpose

To propose automatic segmentation algorithm (AUS) for corneal microlayers on optical coherence tomography (OCT) images.

Methods

Eighty-two corneal OCT scans were obtained from 45 patients with normal and abnormal corneas. Three testing data sets totaling 75 OCT images were randomly selected. Initially, corneal epithelium and endothelium microlayers are estimated using a corneal mask and locally refined to obtain final segmentation. Flat-epithelium and flat-endothelium images are obtained and vertically projected to locate inner corneal microlayers. Inner microlayers are estimated by translating epithelium and endothelium microlayers to detected locations then refined to obtain final segmentation. Images were segmented by trained manual operators (TMOs) and by the algorithm to assess repeatability (i.e., intraoperator error), reproducibility (i.e., interoperator and segmentation errors), and running time. A random masked subjective test was conducted by corneal specialists to subjectively grade the segmentation algorithm.

Results

Compared with the TMOs, the AUS had significantly less mean intraoperator error (0.53 ± 1.80 vs. 2.32 ± 2.39 pixels; P < 0.0001), it had significantly different mean segmentation error (3.44 ± 3.46 vs. 2.93 ± 3.02 pixels; P < 0.0001), and it had significantly less running time per image (0.19 ± 0.07 vs. 193.95 ± 194.53 seconds; P < 0.0001). The AUS had insignificant subjective grading for microlayer-segmentation grading (4.94 ± 0.32 vs. 4.96 ± 0.24; P = 0.5081), but it had significant subjective grading for regional-segmentation grading (4.96 ± 0.26 vs. 4.79 ± 0.60; P = 0.025).

Conclusions

The AUS can reproduce the manual segmentation of corneal microlayers with comparable accuracy in almost real-time and with significantly better repeatability.

Translational Relevance

The AUS can be useful in clinical settings and can aid the diagnosis of corneal diseases by measuring thickness of segmented corneal microlayers.

Evaluation of endothelial/Descemet membrane complex of eye bank donor corneas using enhanced depth imaging optical coherence tomography

Objective: We present a novel method for screening eye bank donor corneas using high definition optical coherence tomography (HD-OCT). This technology allows for the quantification of endothelial/Descemet membrane (En/DM) complex thickness ex vivo.

Design: Prospective interventional study.

Participants: Fifty-two corneal grafts from 27 donors were included in this study. Twenty additional control eyes and 11 eyes with Fuchs’ endothelial corneal dystrophy were also evaluated for comparison.

Methods: A custom built, high speed HD-OCT device (Envisu R2210, Bioptigen, Buffalo Grove, IL, USA) was used to obtain images, and custom-made graph-based segmentation software was used to automatically deconstruct corneal images into micro-layers. HD-OCT imaging was used to scan through the sealed sterile case of donor corneas stored in McCarey-Kaufman medium to image their En/DM complex through the center of the cornea.

Results: This technology allowed for quantification of En/DM complex thickness in all donor corneas through the sealed sterile container used to transport graft tissue. Mean En/DM complex thickness of donor corneas was 17±4 μm. The difference between donor cornea En/DM thickness and that of control subjects (16±2 μm) was not statistically significant (p=0.3), suggesting that the transport container and media do not affect measurements. There was a significant difference between En/DM thickness of Fuchs’ endothelial corneal dystrophy eyes (25±5 μm) and both donor corneas (p<0.0001) and control subjects (p<0.0001).

Conclusions: We have described a new technique to measure En/DM complex thickness in eye bank donor corneas stored in a sealed sterile case. This may represent a novel adjunctive approach to screen corneal grafts for early endothelial disease.

Ocular Injury due to Potassium Permanganate Granules

Purpose

We report a rare case of ocular injury due to potassium permanganate (KMnO₄) granules in a child.

Methods

This is a retrospective case report.

Results

A 2-year-old boy was transferred to our emergency room with severe pain in his right eye, inflamed eyelids, and brownish stains on his fingers. Chemical injury was suspected. Copious eye irrigation was immediately performed. Diffuse brownish splotches were then observed at the inferior bulbar conjunctiva. Otherwise, systemic organs were intact. Complete eye exam under general anesthesia revealed a 5-mm epithelial defect at the central cornea, along with generalized conjunctival injection and limbal ischemia, inferiorly. Multiple semi-dissolved granules of KMnO₄ trapped in the inferior fornix were identified. The chemical particles were gradually washed out and removed; however, the brownish stains remained. The patient received preservative-free steroid, antibiotic eye drops, and lubricants as regular management for mild to moderate degree of ocular burn. Pseudomembrane developed early and transformed into symblepharon within a few days after the injury. Membrane adhesion was lysed, and more aggressive medications were then substituted. Commercial amniotic membrane (PROKERA®) was also applied to promote wound healing and to prevent recurrence of symblepharon. The ocular surface was eventually restored, and corneal transparency was preserved.

Conclusion

Ocular injury with the granular form of KMnO₄ is rare. Its toxicity is comparable to concentrated KMnO₄ solution. However, the dissolved particles that had been absorbed in the stained conjunctiva were continuously released and damaged the ocular surface more than we primarily anticipated. Awareness of this condition and prompt management yield a good treatment outcome.