Review for special issue: Corneal lamellar surgery: Present outcomes and future perspectives.

Since the establishment of the first eye bank in the 1940s, their role has evolved to face new challenges. With the recent development of lamellar keratoplasties, eye banks play an even bigger role in the selection and preparation of donor tissues. The increasing number of keratoplasty techniques and the high demand for "ready-to-use" tissues are challenging eye banks to improve and develop new preparation techniques. Besides necessary examinations, new approaches of tissue analysis in eye banks allow a better/optimized selection of corneal tissues. These new challenges in tissue preservation, preparation, and selection are propelling eye banks into a new era of modern eye banking.

Analysis of Graft Detachments and Re-Bubblings After 450 Descemet Membrane Endothelial Keratoplasty Procedures.

PURPOSE: To objectify the indication for re-bubbling by analyzing graft detachments (GDs) after Descemet membrane endothelial keratoplasty. METHODS: In this retrospective monocentric observational study, re-bubbling cases of 450 Descemet membrane endothelial keratoplasties and the percentage of the residual gas filling (RGF) in the anterior chamber on the first postoperative day were collected. The number/location/extent of GDs and the corneal thickness above GDs were analyzed using anterior segment optical coherence tomography. RESULTS: From a total of 450 grafts, 384 (85.3%) had at least a minimal degree GD. One hundred twenty-two of 450 grafts (27.1%) underwent at least 1 re-bubbling. The mean RGF was significantly lower in eyes with GD (67.7 ± 12.6%) than in eyes without GD (74.2 ± 11.3%). GDs occurred most frequently in the inferotemporal quadrant (46.0%). GDs were significantly more likely to require a re-bubbling when the central parts of the graft were affected (94.0% vs. 35.7%). The number of detachments per graft was directly proportional to the re-bubbling rate. The GDs which required a re-bubbling were on average 56 µm higher and 461 µm wider than the untreated ones. The cornea above the GDs that needed a re-bubbling was significantly thicker than above the untreated GDs (mean 988 ± 102 µm vs. 951 ± 99 µm). CONCLUSIONS: The RGF seems to be a major influencing factor for graft attachment. The most susceptible location of the GD is inferotemporal. The main factors that need to be investigated to decide if a re-bubbling is required are the number of detachments per graft, their dimensions, whether the central portions of the graft are involved, and the corneal thickness above GDs.

Oxidative stress in the eye and its role in the pathophysiology of ocular diseases.

Oxidative stress occurs through an imbalance between the generation of reactive oxygen species (ROS) and the antioxidant defense mechanisms of cells. The eye is particularly exposed to oxidative stress because of its permanent exposure to light and due to several structures having high metabolic activities. The anterior part of the eye is highly exposed to ultraviolet (UV) radiation and possesses a complex antioxidant defense system to protect the retina from UV radiation. The posterior part of the eye exhibits high metabolic rates and oxygen consumption leading subsequently to a high production rate of ROS. Furthermore, inflammation, aging, genetic factors, and environmental pollution, are all elements promoting ROS generation and impairing antioxidant defense mechanisms and thereby representing risk factors leading to oxidative stress. An abnormal redox status was shown to be involved in the pathophysiology of various ocular diseases in the anterior and posterior segment of the eye. In this review, we aim to summarize the mechanisms of oxidative stress in ocular diseases to provide an updated understanding on the pathogenesis of common diseases affecting the ocular surface, the lens, the retina, and the optic nerve. Moreover, we discuss potential therapeutic approaches aimed at reducing oxidative stress in this context.

P06-A143†An artificial-intelligence-based decision support tool for the detection of Cornea guttata on the donor corneas in the eye bank.

PURPOSE: Cornea guttata (CG) prevalence post keratoplasty varies from 15 to 18%, with 1 to 2% of the cases presenting with significant negative outcomes. The purpose of this research project is to create a program based on artificial intelligence (AI) that helps with the detection of CG in the donor corneas (DC) in the eye bank. METHODS: Preoperative corneal endothelial images (PCEI) of patients who underwent keratoplasty were collected and classified into 2 groups according to the postoperative CG grade. Group 1 included healthy corneas and those having mild postoperative CG, while group 2 included corneas with severe postoperative CG. Using previously tested semi-quantitative morphological criteria along with other characteristics such as donor age and lens status, the PCEI were analyzed and used to create and train an AI-based tool for the detection of CG. The underlying concept of the tool compares previous cases with comparable properties to the DC in test. The postoperative CG grades of previous cases similar to the DC in test determine the prediction for its CG grade. Finally, the features and CG grade of the analyzed DC are stored in the database for future use. RESULTS: In total, 6221 PCEI belonging to 1078 patients were used to create a transparent and explainable decision support tool for the detection of CG through a hybrid approach combining 2 components. (1) Graphical analytic tools, whereby the PCEI pass multiple OpenCV-based image processing steps including the Watershed transform algorithm. In this step, cell membranes are delineated, and abnormally large cells or cell depleted areas are marked in red. Several other cell representations such as 'honeycomb' representation are created for an enhanced visualization of the endothelial layer (EL). (2) Machine learning (ML) classifiers including Case-Based Reasoning were created to detect CG. Initial experiments showed a performance comparable to humans (4-fold evaluation yielded precision: weighted F1 score:0.93). CONCLUSION: We presented an AI-based program able to facilitate the detection of CG in the DC in the eye bank by comparing the PCEIs with relevant previous cases, using ML classifiers and offering an enhanced visualization of the EL. The evaluation and optimization of this program will follow as the next stage of our project.

Detecting the corneal neovascularisation area using artificial intelligence.

AIMS: To create and assess the performance of an artificial intelligence-based image analysis tool for the measurement and quantification of the corneal neovascularisation (CoNV) area. METHODS: Slit lamp images of patients with CoNV were exported from the electronic medical records and included in the study. An experienced ophthalmologist made manual annotations of the CoNV areas, which were then used to create, train and evaluate an automated image analysis tool that uses deep learning to segment and detect CoNV areas. A pretrained neural network (U-Net) was used and fine-tuned on the annotated images. Sixfold cross-validation was used to evaluate the performance of the algorithm on each subset of 20 images. The main metric for our evaluation was intersection over union (IoU). RESULTS: The slit lamp images of 120 eyes of 120 patients with CoNV were included in the analysis. Detections of the total corneal area achieved IoU between 90.0% and 95.5% in each fold and those of the non-vascularised area achieved IoU between 76.6% and 82.2%. The specificity for the detection was between 96.4% and 98.6% for the total corneal area and 96.6% and 98.0% for the non-vascularised area. CONCLUSION: The proposed algorithm showed a high accuracy compared with the measurement made by an ophthalmologist. The study suggests that an automated tool using artificial intelligence may be used for the calculation of the CoNV area from the slit-lamp images of patients with CoNV.

Non-invasive endothelial cell density measurement of in toto pre-stripped DMEK-roll - impact of pre- and intraoperative endothelial cell loss on postoperative midterm clinical outcome.

BACKGROUND/OBJECTIVES: To measure the endothelial cell density (ECD) of the in toto pre-stripped endothelial Descemet membrane lamellae (EDML) and to describe the impact of pre- and intraoperative endothelial cell loss (ECL) on postoperative midterm clinical outcome. SUBJECTS/METHODS: The ECD of 56 Corneoscleral Donor Discs (CDD) was first measured with an inverted specular microscope (t0pre). The measurement was then repeated non-invasively after the preparation of the EDML (t0post). DMEK was performed the next day using these grafts. Follow-up examinations took place 6 weeks, 6 months and 1 year postoperatively where the ECD was assessed. In addition, the impact of ECL 1 (during preparation) and ECL 2 (during surgery) on the ECD, visual acuity (VA) and pachymetry at 6 months and 1 year was investigated. RESULTS: The average ECD (in cells/mm²) at time points t0pre, t0post, 6 weeks, 6 months & 1 year was 2584 ± 200, 2355 ± 207, 1366 ± 345, 1091 ± 564 and 939 ± 352. The average logMAR VA and pachymetry (in µm) was 0.50 ± 0.27 and 597 ± 63, 0.23 ± 0.17 and 535 ± 54, 0.16 ± 0.12 and 535 ± 54, 0.06 ± 0.08 and 512 ± 37, respectively The ECL 1 (9% on average) had no significant impact on the main outcome measures after 6 months and 1 year (p > 0.11). The ECL 2 correlated significantly with the ECD and the pachymetry at 1 year postop (p < 0.02). CONCLUSION: Our results indicate that the non-invasive ECD measurement of the prestripped EDML roll before its transplantation is feasible. Despite significantly decreasing ECD up to 6 months postoperatively, visual acuity further improved and thickness further decreased up to 1 year postoperatively.

Prevalence and Impact of Cornea Guttata in the Graft After Penetrating Keratoplasty in Germany.

PURPOSE: The aim of this study was to analyze the prevalence and severity of corneal guttata (CG) in grafts after penetrating keratoplasty (PKP) and to determine its clinical significance. METHODS: This retrospective study included 1758 PKP performed in 1522 patients. In total, 6662 postoperative endothelial images revealed the prevalence and severity of CG (divided into categories G0 without CG and G1-G3 with increasing severity). Origin of the graft, postoperative corneal thickness, visual acuity, pleomorphism, polymegethism, and endothelial cell density (ECD) were analyzed. RESULTS: CG was detected in 14.9% of the grafts within 9 months after PKP, most of them were low-grade G1 (13.6%). Grafts from Homburg/Saar showed significantly less CG cases compared with other eye banks ( P = 0.034). The mean corrected distance visual acuity (logMAR) did not differ between G1 (0.45 ± 0.31) and G0 (0.46 ± 0.31). The mean ECD was lower in G1 compared with G0 ( P < 0.001). The mean corneal thickness was higher in G3 (597 ± 101 µm) compared with G0 (541 ± 65 µm) ( P < 0.001). Pleomorphism and polymegethism were correlated with CG ( P < 0.001). A progression of CG severity was detected in 13.5% of the cases during a follow-up time of 25.0 ± 19.9 months. CONCLUSIONS: Our study suggested that CG are transplanted in 14.9% of PKP, most of which are low-grade CG not affecting the visual acuity but already leading to an increase in corneal thickness, loss of ECD, and alteration of endothelial cell morphology. In 13.5% of the cases, a progression was demonstrated in the postoperative course.

Prevalence and severity of cornea guttata in the graft following Descemet Membrane Endothelial Keratoplasty (DMEK).

PURPOSE: The aim of this study was to determine the prevalence and severity of cornea guttata (CG) in grafts after Descemet membrane endothelial keratoplasty (DMEK) and to investigate its impact on various clinical parameters during follow-up. METHODS: This retrospective study included 664 operations (DMEK and triple-DMEK) on 466 patients. The prevalence and progression of CG after the operation were examined using endothelial specular microscopy images. The severity grade of CG was classified into four grades: G0 without CG, G1 - G3 with increasing severity of CG. Clinical parameters such as central corneal thickness (CCT), visual acuity (VA), endothelial cell density (ECD), pleomorphism and polymegalism were examined during a postoperative follow-up time of 19.6 ± 15.8 months. RESULTS: Cornea guttata (CG) appeared postoperatively in 124 (18.7%) eyes. 112 (16.9%) could be classified as G1, 9 (1.4%) as G2 and only 3 (0.5%) as G3. The examination of clinical parameters showed significant differences between healthy and low-grade CG (G0/G1) and high-grade CG (G2/G3). A significant deterioration was found in the corrected distance visual acuity (CDVA) (p = 0.02). CCT showed an increase between G0 (534 ± 58 µm) and G2 (549 ± 71 µm)/G3 (558 ± 56 µm) with a p-value of 0.02. Additionally, a significant increase in pleomorphism (p = 0.003) and polymegalism (p = 0.04) was detected. CONCLUSION: Cornea guttata (CG) prevalence after DMEK and triple-DMEK was found to be 18.7%, although most of these cases were classified as low-grade CG and showed no clinical significance. Around 1.9% were classified as high-grade CG and significantly affected several clinical parameters during the follow-up.

Semiquantitative Criteria in the Eye Bank That Correlate with Cornea Guttata in Donor Corneas.

BACKGROUND: Cornea guttata may not be recognized in the eye bank and recent studies have displayed that guttae are transplanted in about 15% of cases in varying severities. The purpose of this study was to establish semiquantitative criteria for the detection of cornea guttata in donor corneas in the eye bank. METHODS: In this retrospective cohort study, preoperative endothelial pictures of donor corneas were collected and classified according to the post-penetrating keratoplasty cornea guttata grade into three distinct groups: group 1 consists of healthy corneas with no guttae (guttata grade 0); group 2 constitutes corneas with mild asymptomatic cornea guttata (guttata grade +); and group 3 comprises corneas with advanced widespread cornea guttata (guttata grade ++/+++/++++). The preoperative pictures of each group were then individually analyzed using the following five semiquantitative criteria: The number and the area of the cell-depleted surfaces, the presence of less than 50% of the cells having a hexagonal or a circular shape, the presence of cell membrane defects and interruptions, the presence of blebs in the cell membrane, and the presence of groups of cells with a distinct whitish color. RESULTS: In total, 262 patients were included in this study, with a total number of 1582 preoperative donor corneal endothelial pictures. Out of those pictures, groups 1, 2, and 3 encompassed 995 (62.9%), 411 (26.0%), and 176 (11.1%) pictures, respectively. Three out of the five eye bank criteria were found to correlate with postoperative cornea guttata with a highly significant p value of < 0.001. These three criteria are the presence of less than 50% of the cells having a hexagonal or a circular shape, the presence of cell membrane defects and interruptions and, the presence of blebs. The presence of groups of cells with a distinct whitish color was only a weak predictive factor for cornea guttata (p = 0.069). There was no statistically significant correlation between the number and the area of cell-depleted surfaces and postoperative cornea guttata with a p = 0.181. CONCLUSION: Three semiquantitative criteria that can be detected in the eye bank using inverted light microscopy seem to correlate with postoperative cornea guttata: The presence of blebs, the presence of cell membrane defects and interruptions, as well as endothelial pictures with less than 50% of the cells having a hexagonal of circular shape. The presence of groups of cells with a distinct whitish color appears to be a weak predictor of cornea guttata.

[Excimer laser-assisted DALK: a case report from the Homburg Keratoconus Center (HKC)]. / Excimerlaser-gestützte DALK: Ein Fallbericht aus dem Homburger Keratokonus Center (HKC).

INDICATIONS: The aim of excimer laser-assisted deep anterior lamellar keratoplasty (excimer-DALK) is, as in mechanical DALK, the treatment of keratectasia (keratoconus and pellucid marginal degeneration), stromal scars or stromal corneal dystrophy. A prerequisite for surgery is the absence of (pre­) Descemet's scars and an intact endothelium. SURGICAL TECHNIQUE: After excimer laser-assisted trephination to 80% of the corneal thickness at the trephination site, intrastromal air injection (so-called big bubble) and lamellar corneal preparation, a lamellar anterior transplantation of the endothelium-free donor tissue is performed. The technique combines the advantages of DALK and excimer laser trephination. We describe the steps of an excimer-DALK from the Homburg Keratoconus Center (HKC). CONCLUSION: Excimer-DALK is a viable treatment option for patients with intact endothelium. In cases of intraoperative perforation, conversion to excimer-perforating keratoplasty (PKP) with all the advantages of excimer laser trephination remains feasible.

Reproducibility of Non-Invasive Endothelial Cell Loss Assessment of the Pre-Stripped DMEK Roll After Preparation and Storage.

PURPOSE: To present a novel, reproducible, and noninvasive method to quantify endothelial cell loss (ECL) of pre-stripped endothelial Descemet membrane lamellae (EDML) caused by its preparation and storage for 5 days. DESIGN: Prospective laboratory investigation. METHODS: Thirty EDML were stripped from corneoscleral discs and placed in a well plate containing organ culture medium 1 without dextran. An additional 5 corneoscleral discs were also placed in the same medium and served as a control group. Endothelial cell density (ECD) was measured without any additional manipulation by using spectral microscopy following an extensive protocol by which 3 clear images from the center and periphery were used for each measurement, and each measurement was repeated 5 times. ECD was measured before and directly after preparation and on days 1, 2, and 5 of storage. RESULTS: The average ECD of the 30 corneoscleral discs, which later underwent stripping, was 2,292 ± 308 cells/mm2 vs 2,129 ± 222 cells/mm2 for the 5 corneoscleral discs of the control group. The ECL of the control group was significantly lower than that of the EDML group (P < .0001), reaching ±2% versus 11 ± 5%, respectively, on day 0; 3% ± 4% versus 19 ± 10%, respectively, on day 1; 2% ± 2% versus 22% ± 11%, respectively on day 2; and 4% ± 3% versus 23% ± 9%, respectively, on day 5. Reproducibility of the results on all measurement days was good, with Cronbach alpha values ranging from 0.85 to 0.98. CONCLUSIONS: A highly reproducible, noninvasive method was presented for measuring the ECD of the EDML. Prestripped EDML lose a significant amount of cells, up to 11%, due to the preparation process and up to 23% after 5 days of storage. Therefore, shipping them after several days of storage to be used in a DMEK surgery cannot be recommended.