Comparison of confocal biomicroscopy and noncontact specular microscopy for evaluation of the corneal endothelium

Review of the Literature: Surgery Indications for Fuchs' Endothelial Corneal Dystrophy

Objectives: To provide an overview of the preoperative indications for endothelial graft in patients with Fuchs endothelial corneal dystrophy (FECD). Methods: A comprehensive database search without date restrictions was performed in PubMed. Keywords included Descemet membrane endothelial keratoplasty (DMEK), Descemet stripping automated endothelial keratoplasty (DSAEK), corneal keratoplasty, preoperative visual acuity, preoperative central corneal thickness, and densitometry. Articles aiming to describe or evaluate preoperative indications for endothelial keratoplasty were considered eligible and were included in this review. Results: The indications for surgery in FECD are disparate between the different studies. The tendency is to operate on patients earlier to obtain a better postoperative visual acuity at 1 year. The surgical decision is based on a number of arguments (visual acuity, CCT, densitometry). A preoperative visual acuity worse than 20/40 is generally considered a surgical indication for DMEK, based on current literature. Conclusions: Surgical decisions for Fuchs' dystrophy should be individualized, guided by preoperative visual acuity, corneal OCT, and advanced imaging, with future risk scores potentially refining the timing of intervention to optimize outcomes.

Machine learning based endothelial cell image analysis of patients undergoing descemet membrane endothelial keratoplasty surgery

OBJECTIVES

In this study, we developed a machine learning approach for postoperative corneal endothelial cell images of patients who underwent Descemet's membrane keratoplasty (DMEK).

METHODS

An AlexNet model is proposed and validated throughout the study for endothelial cell segmentation and cell location determination. The 506 images of postoperative corneal endothelial cells were analyzed. Endothelial cell detection, segmentation, and determining of its polygonal structure were identified. The proposed model is based on the training of an R-CNN to locate endothelial cells. Next, by determining the ridges separating adjacent cells, the density and hexagonality rates of DMEK patients are calculated.

RESULTS

The proposed method reached accuracy and F1 score rates of 86.15 % and 0.857, respectively, which indicates that it can reliably replace the manual detection of cells in vivo confocal microscopy (IVCM). The AUC score of 0.764 from the proposed segmentation method suggests a satisfactory outcome.

CONCLUSIONS

A model focused on segmenting endothelial cells can be employed to assess the health of the endothelium in DMEK patients.

Fuchs' Endothelial Corneal Dystrophy evaluation using a high-resolution wavefront sensor

This study aims to evaluate the applicability of the high-resolution WaveFront Phase Imaging Sensor (WFPI) in eyes with Fuchs' Endothelial Corneal Dystrophy (FECD) through qualitative and quantitative analysis using a custom-designed Automatic Guttae Detection Method (AGDM). The ocular phase was measured using the t · eyede aberrometer and then was processed to obtain its High-Pass Filter Map (HPFM). The subjects were pathological and healthy patients from the Fundación Jiménez-Díaz Hospital (Madrid, Spain). The AGDM was developed and applied in pupils with 3 and 5 mm of diameter. A set of metrics were extracted and evaluated like the Root-Mean-Square error (RMS), Number of guttae, Guttae Area, and Area of Delaunay Triangulation (DT). Finally, a Support Vector Machine (SVM) model was trained to classify between pathological and healthy eyes. Quantitatively, the HPFM reveals a dark spots pattern according to the ophthalmologist's description of the slit-lamp examination of guttae distribution. There were significant statistical differences in all the metrics when FECD and Healthy groups were compared using the same pupil size; but comparing both pupil sizes for the same group there were significant differences in most of the variables. This sensor is a value tool to objectively diagnose and monitor this pathology through wavefront phase changes.

Applications of Imaging Technologies in Fuchs Endothelial Corneal Dystrophy: A Narrative Literature Review

Fuchs endothelial corneal dystrophy (FECD) is a complex genetic disorder characterized by the slow and progressive degeneration of corneal endothelial cells. Thus, it may result in corneal endothelial decompensation and irreversible corneal edema. Moreover, FECD is associated with alterations in all corneal layers, such as thickening of the Descemet membrane, stromal scarring, subepithelial fibrosis, and the formation of epithelial bullae. Hence, anterior segment imaging devices that enable precise measurement of functional and anatomical changes in the cornea are essential for the management of FECD. In this review, the authors will introduce studies on the application of various imaging modalities, such as anterior segment optical coherence tomography, Scheimpflug corneal tomography, specular microscopy, in vitro confocal microscopy, and retroillumination photography, in the diagnosis and monitoring of FECD and discuss the results of these studies. The application of novel technologies, including image processing technology and artificial intelligence, that are expected to further enhance the accuracy, precision, and speed of the imaging technologies will also be discussed.

Diabetic Retinopathy: Soluble and Imaging Ocular Biomarkers

Diabetic retinopathy (DR), the most common microvascular complication of diabetes mellitus, represents the leading cause of acquired blindness in the working-age population. Due to the potential absence of symptoms in the early stages of the disease, the identification of clinical biomarkers can have a crucial role in the early diagnosis of DR as well as for the detection of prognostic factors. In particular, imaging techniques are fundamental tools for screening, diagnosis, classification, monitoring, treatment planning and prognostic assessment in DR. In this context, the identification of ocular and systemic biomarkers is crucial to facilitate the risk stratification of diabetic patients; moreover, reliable biomarkers could provide prognostic information on disease progression as well as assist in predicting a patient's response to therapy. In this context, this review aimed to provide an updated and comprehensive overview of the soluble and anatomical biomarkers associated with DR.

A Fully Automated Segmentation and Morphometric Parameter Estimation System for Assessing Corneal Endothelial Cell Images

PURPOSE

To develop a fully automated segmentation and morphometric parameter estimation system for assessing corneal endothelial cells from in vivo confocal microscopy images.

DESIGN

Artificial intelligence (neural network) study.

METHODS

First, a fully automated deep learning system for assessing corneal endothelial cells was developed using the development set (from 99 subjects). Second, 184 images (from 97 subjects) were used to construct the testing set to evaluate the clinical validity and usefulness of the automated segmentation and morphometric system. Third, the automatically calculated endothelial cell density (ECD) values, Topcon's cell density, and manually calculated ECD were compared.

RESULTS

After slit lamp examination, 88 healthy subjects, 2 Fuchs endothelial dystrophy patients, and 7 corneal endotheliitis patients were identified among the 97 subjects in the testing set. The automatedly estimated morphometric parameters for the testing set were an average number of 234 cells, an ECD of 2592 cells/mm², a coefficient of variation in the cell area of 32.14%, and a percentage of hexagonal cells of 54.16%. Pearson's correlation coefficient between the automated ECD and Topcon's cell density and between the manually calculated ECD and Topcon's cell density was 0.932 (P < .01) and 0.818 (P < .01), respectively. The Bland-Altman plot of Topcon's cell density and the automated ECD yielded 95% limits of agreement between 271.94 and -572.46 (concordance correlation coefficient = 0.9).

CONCLUSIONS

A fully automated method for segmenting corneal endothelial cells and estimating morphometric parameters using in vivo confocal microscopy images is more efficient and accurate for assessing the normal corneal endothelium.

Long-term Outcomes of Descemet Stripping Endothelial Keratoplasty: Ten-Year Graft Survival and Endothelial Cell Loss

PURPOSE

To determine 10-year outcomes for graft and endothelial cell survival after Descemet stripping endothelial keratoplasty (DSEK), including risk factors for graft failure.

DESIGN

Retrospective clinical cohort study.

METHODS

Three hundred fifty-six consecutive DSEK grafts performed by 10 surgeons using a standardized protocol were analyzed. Primary outcomes were cumulative graft survival and percentage endothelial cell loss (ECL) from 6 months to 10 years; secondary outcomes included risk factors for graft failure, postoperative complications, visual outcomes, and central corneal thickness.

RESULTS

Indications include Fuchs endothelial dystrophy (n = 209), bullous keratopathy (n = 88), and previous graft failure (n = 39). One hundred and four eyes (29%) had preoperative glaucoma. Cumulative graft survival rates of all eyes at 1, 3, 5, and 10 years were 97%, 90%, 85%, and 79%, respectively. Ten-year graft survival for Fuchs endothelial dystrophy was 92%. Mean ± SD percentage ECL of all grafts was 46.6% ± 17.3% at year 1, 54.9% ± 18.7% at year 3, 59.6% ± 17.4% at year 5, and 73.1% ± 9.7% at year 10. Cox regression identified preoperative glaucoma (hazard ratio [HR]: 8.41; 95% CI, 1.30-54.5; P = .026), including previous glaucoma surgery (HR: 3.63; 95% CI: 1.03-12.74; P = .04) and regrafts (HR: 5.29; 95% CI: 2.02-13.89; P = .001) as significant risk factors for graft failure.

CONCLUSIONS

At 10 years, DSEK survival rate was 79% for all eyes, including complex grafts, and ECL was 73%. For Fuchs endothelial dystrophy, 10-year graft survival rate was 92%. Despite a mean 10-year endothelial cell count of only 692 cells/mm², graft survival remained high with good vision. DSEK continues to be a viable treatment option, especially in complex eyes with comorbidity.

An automatic approach for cell detection and segmentation of corneal endothelium in specular microscope

PURPOSE

Specular microscopy is an indispensable tool for clinicians seeking to monitor the corneal endothelium. Automated methods of determining endothelial cell density (ECD) are limited in their ability to analyze images of poor quality. We describe and assess an image processing algorithm to analyze corneal endothelial images.

METHODS

A set of corneal endothelial images acquired with a Konan CellChek specular microscope was analyzed using three methods: flex-center, Konan Auto Tracer, and the proposed method. In this technique, the algorithm determines the region of interest, filters the image to differentiate cell boundaries from their interiors, and utilizes stochastic watershed segmentation to draw cell boundaries and assess ECD based on the masked region. We compared ECD measured by the algorithm with manual and automated results from the specular microscope.

RESULTS

We analyzed a total of 303 images manually, using the Auto Tracer, and with the proposed image processing method. Relative to manual analysis across all images, the mean error was 0.04% in the proposed method (p = 0.23 for difference) whereas Auto Tracer demonstrated a bias towards overestimation, with a mean error of 5.7% (p = 2.06× 10^-8). The relative mean absolute errors were 6.9% and 7.9%, respectively, for the proposed and Auto Tracer. The average time for analysis of each image using the proposed method was 2.5 s.

CONCLUSION

We demonstrate a computationally efficient algorithm to analyze corneal endothelial cell density that can be implemented on devices for clinical and research use.

Fuchs endothelial corneal dystrophy: The vicious cycle of Fuchs pathogenesis

Fuchs endothelial corneal dystrophy (FECD) is the most common primary corneal endothelial dystrophy and the leading indication for corneal transplantation worldwide. FECD is characterized by the progressive decline of corneal endothelial cells (CECs) and the formation of extracellular matrix (ECM) excrescences in Descemet's membrane (DM), called guttae, that lead to corneal edema and loss of vision. FECD typically manifests in the fifth decades of life and has a greater incidence in women. FECD is a complex and heterogeneous genetic disease where interaction between genetic and environmental factors results in cellular apoptosis and aberrant ECM deposition. In this review, we will discuss a complex interplay of genetic, epigenetic, and exogenous factors in inciting oxidative stress, auto(mito)phagy, unfolded protein response, and mitochondrial dysfunction during CEC degeneration. Specifically, we explore the factors that influence cellular fate to undergo apoptosis, senescence, and endothelial-to-mesenchymal transition. These findings will highlight the importance of abnormal CEC-DM interactions in triggering the vicious cycle of FECD pathogenesis. We will also review clinical characteristics, diagnostic tools, and current medical and surgical management options for FECD patients. These new paradigms in FECD pathogenesis present an opportunity to develop novel therapeutics for the treatment of FECD.

Corneal endothelial cell loss following cataract surgery in patients with pseudoexfoliation syndrome: a 2-year prospective comparative study

PURPOSE

To compare the corneal endothelial cell density (ECD) before and after cataract surgery in patients with and without pseudoexfoliation syndrome (PEX).

METHODS

In this prospective study, we compared the ECD in 62 PEX patients with 62 patients without PEX (controls). The mean age was 78.3 ± 6.2 years and 77.2 ± 5.9 years, respectively. Patients were examined before and at 6 months, 1 year and 2 years after cataract surgery. The corneal endothelium was examined with confocal microscopy, and the ECD was counted both automatically and semi-manually. Nine patients in the PEX group (15%) and 11 patients in the control group (18%) were lost to follow-up in the 2-year period. Within the PEX and the control groups, we also compared the ECD between patients with and without glaucoma.

RESULTS

Before surgery, the ECD (semi-manual counting) was 2258 ± 342 cells/mm² in the PEX group and 2322 ± 321 cells/mm² in the control group (p = 0.29). There were no significant differences in postoperative ECD between these groups at any visit. After 2 years, the ECD had changed by -679 ± 337 cells/mm² and -704 ± 484 cells/mm² , respectively (p = 0.78). The preoperative ECD was lower in eyes with glaucoma compared to eyes without glaucoma, both within the PEX group (p = 0.05) and the control group (p = 0.03). After surgery, there were no differences between eyes with or without glaucoma.

CONCLUSION

The ECD was not significantly different in PEX eyes compared with control eyes, neither before nor after cataract surgery. However, there seemed to be a lower ECD in eyes with glaucoma before surgery.

Imaging the Corneal Endothelium in Fuchs Corneal Endothelial Dystrophy

Fuchs endothelial corneal dystrophy (FECD) is characterized by the progressive degeneration of the corneal endothelium (CE). The purpose of this article is to review the diagnostic tools available to image and assess the CE in FECD. Slit-lamp biomicroscopy with specular reflection and retroillumination are important techniques to assess the CE. Objective diagnostic tests, such as retroillumination photographic analysis, specular microscopy, in vivo confocal microscopy (IVCM), and anterior segment optical coherence tomography, are valuable tools to evaluate the CE in FECD. Specular microscopy can be performed rapidly without touching the eye but requires a clear cornea with a smooth CE. In contrast, IVCM can image all layers of the cornea, even in advanced FECD. However, IVCM is contact-based and more technically challenging. It is important to select the appropriate objective diagnostic test to image and assess the CE in managing patients with FECD.

Regional variability in corneal endothelial cell density between guttae and non-guttae areas in Fuchs endothelial corneal dystrophy

OBJECTIVE

To assess the regional variability of corneal endothelial cell density (ECD) between guttae and non-guttae areas in subjects with Fuchs endothelial corneal dystrophy (FECD) using non-contact specular microscopy and confocal microscopy.

DESIGN

Retrospective chart review from 2009 to 2014 at the Massachusetts Eye and Ear Infirmary.

PARTICIPANTS

One hundred fifteen eyes of 73 subjects with FECD.

METHODS

Subjects with FECD underwent same-day specular and confocal microscopy in the same eye. Clinical stage of disease was documented on the day of image acquisition. Regional variability of ECD associated with guttae and non-guttae areas was assessed. Manual endothelial cell counts were performed.

RESULTS

Thirty-two percent of subjects had high quality endothelial images by both specular and confocal microscopy. Of these subjects, 83% were classified clinically as early-stage FECD. There was a significant association between stage of disease and the ability to obtain high quality specular images (χ²; p = 0.0012). There was no difference in mean ECD derived from specular (1363 ± 594 cells/mm²) or confocal (1391 ± 493 cells/mm²; p = 0.75) images. There was a statistically significant decrease of 31.8 ± 21.7% in mean ECD in areas surrounding guttae (1296 ± 560 cells/mm²) compared to non-guttae areas (1926 ± 674 cells/mm²; p < 0.0001) as determined by confocal microscopy.

CONCLUSION

These findings support confocal microscopy as an alternative to specular microscopy for evaluating the corneal endothelium of patients with FECD, especially those with advanced disease. Confocal microscopy also revealed regional differences in ECD in guttae and non-guttae areas in patients with FECD.

Fully convolutional architecture vs sliding-window CNN for corneal endothelium cell segmentation

Background

Corneal endothelium (CE) images provide valuable clinical information regarding the health state of the cornea. Computation of the clinical morphometric parameters requires the segmentation of endothelial cell images. Current techniques to image the endothelium in vivo deliver low quality images, which makes automatic segmentation a complicated task. Here, we present two convolutional neural networks (CNN) to segment CE images: a global fully convolutional approach based on U-net, and a local sliding-window network (SW-net). We propose to use probabilistic labels instead of binary, we evaluate a preprocessing method to enhance the contrast of images, and we introduce a postprocessing method based on Fourier analysis and watershed to convert the CNN output images into the final cell segmentation. Both methods are applied to 50 images acquired with an SP-1P Topcon specular microscope. Estimates are compared against a manual delineation made by a trained observer.

Results

U-net (AUC=0.9938) yields slightly sharper, clearer images than SW-net (AUC=0.9921). After postprocessing, U-net obtains a DICE=0.981 and a MHD=0.22 (modified Hausdorff distance), whereas SW-net yields a DICE=0.978 and a MHD=0.30. U-net generates a wrong cell segmentation in only 0.48% of the cells, versus 0.92% for the SW-net. U-net achieves statistically significant better precision and accuracy than both, Topcon and SW-net, for the estimates of three clinical parameters: cell density (ECD), polymegethism (CV), and pleomorphism (HEX). The mean relative error in U-net for the parameters is 0.4% in ECD, 2.8% in CV, and 1.3% in HEX. The computation time to segment an image and estimate the parameters is barely a few seconds.

Conclusions

Both methods presented here provide a statistically significant improvement over the state of the art. U-net has reached the smallest error rate. We suggest a segmentation refinement based on our previous work to further improve the performance.

In Vivo Confocal Microscopy Shows Alterations in Nerve Density and Dendritiform Cell Density in Fuchs' Endothelial Corneal Dystrophy

PURPOSE

To evaluate corneal nerve and immune cell alterations in Fuchs' endothelial corneal dystrophy (FECD) and pseudophakic bullous keratopathy (PBK) by laser in vivo confocal microscopy (IVCM) as correlated to corneal sensation and endothelial cell loss.

DESIGN

Prospective, cross-sectional, controlled study.

METHODS

Thirty-three eyes with FECD were compared to 13 eyes with PBK and 17 normal age-matched control eyes at a tertiary referral center. FECD was classified into early (without edema) and late stage (with edema). Corneal IVCM and esthesiometry were performed. Corneal nerve and immune dendritiform cell (DC) alterations were evaluated and correlated to clinical parameters.

RESULTS

FECD and PBK eyes showed significantly (P = .001) diminished total nerve length (11.5 ± 1.3 and 2.9 ± 0.7 mm/mm²) and number (8.8 ± 1.1 and 2.2 ± 0.4 n/frame), compared to controls (23.3 ± 8.1 mm/mm² and 25.9 ± 1.3 n/frame). Decreased nerves corresponded to diminished sensation in FECD (4.9 ± 0.2 cm; R = 0.32; P = .045), compared to controls (5.9 ± 0.04 cm). Early- and late-stage FECD showed significantly reduced total nerve length (13.1 ± 1.4 and 9.9 ± 1.2 mm/mm², respectively) and number (8.2 ± 2.5 and 6.5 ± 2.1 n/frame), compared to controls (P < .001). DC density was significantly increased in FECD (57.8 ± 10.4 cells/mm²; P = .01), but not in PBK (47.7 ± 11.6 cells/mm²; P = .60) compared to controls (22.5 ± 4.5 cells/mm²). A subset of early FECD patients (7/22) demonstrated very high DC density (>100/mm²).

CONCLUSION

IVCM demonstrates profound diminishment of subbasal corneal nerves in early- and late-stage FECD and in PBK, correlating to decreased sensation. Increased DC density in early FECD demonstrates potential subclinical inflammation. The data suggest that reduction in subbasal nerves and increased immune activation may play a role in the pathophysiology of FECD.

Comparison of Noncontact Specular and Confocal Microscopy for Evaluation of Corneal Endothelium

PURPOSE

To compare endothelial cell analysis obtained by noncontact specular and confocal microscopy, using the Konan NSP-9900 and Nidek ConfoScan4 systems, respectively.

METHODS

Three groups including 70 healthy eyes, 49 eyes with Fuchs endothelial corneal dystrophy (FECD), and 78 eyes with glaucoma were examined with both the Konan NSP-9900 specular microscope and the Nidek ConfocScan4 confocal microscope. Certified graders at the Doheny Image Reading Center compared corneal endothelial images from both instruments side by side to assess image quality. Endothelial cell density (ECD) measurements were calculated and compared using three different modalities: (1) each instrument's fully automated analysis; (2) each instrument's semiautomatic analysis with grader input; and (3) manual grading methods by certified grader.

RESULTS

All normal eyes yielded gradable endothelial images, and most but not all glaucomatous eyes yielded images with high enough image quality to allow grading. In addition, in corneas with severe FECD, poor image quality precluded ECD grading by specular microscopy in 20 eyes (40.8%) but in only 4 (8.2%) confocal images from the same eyes. For the gradable images, the ECD values obtained using the manual grading method from either device were comparable with no statistically significant difference (P>0.05) between specular and confocal devices. Machine-generated ECD values were significantly different from manual results, measuring greater in all cases with specular microscopy. Machine-generated ECD values from confocal microscopy also differed significantly from manual determinations, but not in a consistent direction. Semiautomatic methods for both instruments obtained clinically acceptable ECD values.

CONCLUSIONS

Automatic machine-generated ECD measurements differed significantly from manual assessments of corneal endothelium by both specular and confocal microscopy, suggesting that automated results should be used with caution. But ECD values derived manually were comparable between the two devices in both normal and glaucomatous eyes, suggesting that manually graded images from the two instruments can be used interchangeably for reliable ECD measurements. Because of a higher proportion of gradable images, confocal microscopy may be superior to specular microscopy for ECD measurements in FECD.

Corneal Endothelial Cell Segmentation by Classifier-Driven Merging of Oversegmented Images

Corneal endothelium images obtained by in vivo specular microscopy provide important information to assess the health status of the cornea. Estimation of clinical parameters, such as cell density, polymegethism, and pleomorphism, requires accurate cell segmentation. State-of-the-art techniques to automatically segment the endothelium are error-prone when applied to images with low contrast and/or large variation in cell size. Here, we propose an automatic method to segment the endothelium. Starting with an oversegmented image comprised of superpixels obtained from a stochastic watershed segmentation, the proposed method uses intensity and shape information of the superpixels to identify and merge those that constitute a cell, using support vector machines. We evaluated the automatic segmentation on a data set of in vivo specular microscopy images (Topcon SP-1P), obtaining 95.8% correctly merged cells and 2.0% undersegmented cells. We also evaluated the parameter estimation against the results of the vendor's built-in software, obtaining a statistically significant better precision in all parameters and a similar or better accuracy. The parameter estimation was also evaluated on three other data sets from different imaging modalities (confocal microscopy, phase-contrast microscopy, and fluorescence confocal microscopy) and tissue types (ex vivo corneal endothelium and retinal pigment epithelium). In comparison with the estimates of the data sets' authors, we achieved statistically significant better accuracy and precision in all parameters except pleomorphism, where a similar accuracy and precision were obtained.

Peripheral Endothelial Cell Count Is a Predictor of Disease Severity in Advanced Fuchs Endothelial Corneal Dystrophy

PURPOSE

In advanced Fuchs endothelial corneal dystrophy (FECD), central endothelial changes do not correlate with disease severity. The peripheral endothelial cell count (ECC) has not been studied as a marker of FECD severity. The goal of this study was to determine the relationship between the peripheral ECC and known clinical markers of FECD in advanced cases.

METHODS

Patients with FECD examined between January 1, 2013, and September 1, 2016, by 1 cornea specialist were identified. Medical records from all previous visits were reviewed to include eyes with high-quality central and peripheral in vivo confocal microscopy images performed on the same day as a clinical evaluation. Endothelial photographs were used to perform manual cell counts centrally and peripherally. Clinical grading of FECD from 1 to 4 was performed at the slit-lamp.

RESULTS

We identified 154 eyes of 126 patients that met criteria for inclusion. With higher disease grades, central ECC and peripheral ECC decreased, visual acuity worsened, and central corneal thickness (CCT) increased (all P < 0.05). In patients with advanced disease (defined as either grade 3 or 4, CCT >700, or central ECC <350), the peripheral ECC was the best predictor of disease severity and had the highest number of statistically significant correlations with other clinical markers compared with competing variables.

CONCLUSIONS

In advanced FECD, severity is best determined by the peripheral ECC compared with the central ECC, visual acuity, clinical disease grade, and CCT. The peripheral ECC should be added to the clinical parameters used to evaluate FECD severity.

In Vivo Imaging of Corneal Endothelial Dystrophy in Boston Terriers: A Spontaneous, Canine Model for Fuchs' Endothelial Corneal Dystrophy

Purpose

Boston Terriers (BTs) have a greater prevalence of corneal endothelial dystrophy (CED), in comparison to other canine breeds. Similar to Fuchs' endothelial corneal dystrophy (FECD), this condition is characterized by endothelial cell degeneration with secondary corneal edema. This study assessed corneal morphology using in vivo confocal microscopy (IVCM) and Fourier-domain optical coherence tomography (FD-OCT) in BTs with and without CED.

Methods

The corneas of 16 BTs with CED and 15 unaffected, age-matched BTs underwent clinical evaluation and were imaged using IVCM and FD-OCT. A two-sample t-test or Mann-Whitney rank sum test were used to statistically compare parameters between groups. Data are presented as mean ± SD or median (range).

Results

Mean age did not significantly differ between affected and unaffected dogs at 10.0 ± 2.0 and 10.6 ± 2.4 years, respectively (P = 0.437). Females (69%) were overrepresented among the CED-affected dogs. In CED patients, IVCM demonstrated endothelial polymegathism and pleomorphism. Corneal endothelial density was significantly less (P < 0.001) in dogs with CED (1026 ± 260 cells/mm²) versus age-matched controls (2297 ± 372 cells/mm²). Fourier-domain OCT demonstrated a significant increase (P < 0.01) in central corneal and endothelium-Descemet's complex thickness in dogs with CED versus age-matched controls at 1019 (485–1550) or 536 (464–650) μm and 32 (22–56) or 25 (15–34) μm, respectively.

Conclusions

Corneal endothelial dystrophy in BTs is a bilateral, adult-onset condition that shares many similarities with FECD. Thus, CED could serve as a spontaneous disease model to study the pathogenesis of and develop novel treatments for FECD.

Variable-Size Bead Layer as Standard Reference for Endothelial Microscopes

PURPOSE

For morphometric analysis of the cell mosaic of corneal endothelium, checking accuracy and precision of instrumentation is a key step. In this study, a standard reference sample is proposed, developed to reproduce the cornea with its shape and the endothelium with its intrinsic variability in the cell size.

METHODS

A polystyrene bead layer (representing the endothelium) was deposited on a lens (representing the cornea). Bead diameters were 20, 25, and 30 μm (fractions in number 55%, 30%, and 15%, respectively). Bead density and hexagonality were simulated to obtain the expected true values and measured using a slit-lamp endothelial microscope applied to 1) a Takagi 700GL slit lamp at 40× magnification (recommended standard setup) and 2) a Takagi 2ZL slit lamp at 25× magnification.

RESULTS

The simulation provided the expected bead density 2001 mm and hexagonality 47%. At 40×, density and hexagonality were measured to be 2009 mm (SD 93 mm) and 45% (SD 3%). At 25× on a different slit lamp, the comparison between measured and expected densities provided the factor 1.526 to resize the image and to use the current algorithms of the slit-lamp endothelial microscope for cell recognition.

CONCLUSIONS

A variable-size polystyrene bead layer on a lens is proposed as a standard sample mimicking the real shape of the cornea and the variability of cell size and cell arrangement of corneal endothelium. The sample is suggested to evaluate accuracy and precision of cell density and hexagonality obtained by different endothelial microscopes, including a slit-lamp endothelial microscope applied to different slit lamps, also at different magnifications.

Evaluation of UVA Cytotoxicity for Human Endothelium in an Ex Vivo Corneal Cross-linking Experimental Setting

PURPOSE

To evaluate endothelial cytotoxicity after exposure of human corneas to ultraviolet-A (UVA) (λ = 365 nm; 5.4 J/cm(2)) in an experimental ex vivo corneal cross-linking setting.

METHODS

Sixteen pairs of human donor corneas were cut into two pieces. One piece of each cornea was treated with 0.025% riboflavin solution prior to UVA irradiation (5 minutes; 18 mW/cm(2)), whereas the other piece was not irradiated but treated with riboflavin (right eye) or preservation medium (left eye). By irradiating from the endothelial side, the UVA dosage applied to endothelial cells exceeded at least eight times the cytotoxic threshold established in animal models (0.65 J/cm(2)). Endothelial cell counts were performed by two independent investigators after storage (4 to 5 days at 31 °C) and staining (trypan blue, alizarin red). Normality (Q-Q plot; Shapiro-Wilk test) and equivalence (mixed-effects modeling with a 10% equivalence threshold) of the endothelial cell counts of the different groups were evaluated.

RESULTS

Equivalence of mean endothelial cell density between both groups was observed: 2,237 ± 208 cells/mm(2) in UVA-irradiated pieces and 2,290 ± 281 cells/mm(2) in control pieces (mean difference of 53 ± 240 cells/mm(2) between both groups).

CONCLUSIONS

Despite direct irradiation of human donor endothelium using the clinical dosage for cross-linking, equivalence in endothelial cell counts was observed between irradiated tissues and controls. Ex vivo human corneal endothelial cells seem to be far more resistant to riboflavin-enhanced UVA irradiation than previously estimated by animal experiments.

Morphometric Analyses by a New Slit-Lamp Endothelial Biomicroscope

PURPOSE

A method called EndoKer was recently devised for the morphometric analysis of the cell mosaic of the corneal endothelium. Fully automatic cell recognition is performed on images acquired by a slit-lamp biomicroscope. The aim of this study was to evaluate the accuracy of the EndoKer results.

METHODS

Analyses were performed on a polystyrene bead layer stratified on a contact lens and in vivo on 30 adults. Accuracy was evaluated by comparing the results of EndoKer with the true values obtained by manual counting of the cells in the same images. EndoKer results were also compared with those obtained with the Tomey EM3000 microscope.

RESULTS

The accuracy of the results compared with the manual counting on the same images showed a difference of a few percent for the cell density and for hexagonality. This high accuracy derives from (1) the resolution of the slit-lamp images and (2) the improved cell recognition of the fully automatic method. A good agreement was also found between EndoKer and the Tomey EM3000 microscope results.

CONCLUSIONS

Based on the investigated 30 cases, the slit-lamp biomicroscope may be a viable alternative to dedicated endothelial instruments, providing the additional advantages of a larger investigated area and the possibility to take images of different portions of the cornea. The calibration was performed during the development of the method by using polystyrene beads. The user is not required to perform this calibration. However, such a calibrated sample is suggested for those interested.

Laser Scanning In Vivo Confocal Microscopy of Clear Grafts after Penetrating Keratoplasty

PURPOSE

To evaluate the changes of keratocytes and dendritic cells in the central clear graft by laser scanning in vivo confocal microscopy after penetrating keratoplasty (PK).

METHODS

Thirty adult subjects receiving PK at Shandong Eye Institute and with clear grafts and no sign of immune rejection after surgery were recruited into this study, and 10 healthy adults were controls. The keratocytes and dendritic cells in the central graft were evaluated by laser scanning confocal microscopy, as well as epithelium cells, keratocytes, corneal endothelium cells, and corneal nerves (especially subepithelial plexus nerves).

RESULTS

Median density of subepithelial plexus nerves, keratocyte density in each layer of the stroma, and density of corneal endothelium cells were all lower in clear grafts than in controls. The dendritic cells of five (16.7%) patients were active in Bowman's membrane and stromal membrane of the graft after PK.

CONCLUSIONS

Activated dendritic cells and Langerhans cells could be detected in some of the clear grafts, which indicated that the subclinical stress of immune reaction took part in the chronic injury of the clear graft after PK, even when there was no clinical rejection episode.

Safety of high-intensity corneal collagen crosslinking

PURPOSE

To evaluate the safety of a new high-intensity corneal collagen crosslinking (CXL) treatment protocol for keratoconus.

SETTING

Vardinoyiannion Eye Institute of Crete, Faculty of Medicine, University of Crete, Heraklion, Crete, Greece.

DESIGN

Prospective interventional case series.

METHODS

Patients with progressive keratoconus had CXL using a new treatment protocol with 9 mW/cm(2) irradiance for duration of 10 minutes. The rate of reepithelialization, endothelial cell density (ECD), corrected distance visual acuity (CDVA), and steep and flat keratometry (K) values were evaluated preoperatively and 3 months postoperatively.

RESULTS

Nine patients (10 eyes) were enrolled. No intraoperative or early postoperative complications were observed in any patient. The ECD did not change significantly 3 months postoperatively (P=.169). The CDVA improved from 0.19 logMAR ± 0.20 (SD) preoperatively to 0.10 ± 0.16 logMAR 3 months postoperatively; however, the improvement did not attain significance (P=.141). No eye lost lines of CDVA. The mean steep K readings decreased significantly from 48.04 ± 2.57 diopters (D) preoperatively to 46.51 ± 2.81 D 3 months postoperatively (P=.047); the mean flat K readings did not change significantly postoperatively (P=.285).

CONCLUSIONS

Corneal collagen crosslinking at 9 mW/cm(2) irradiance for 10 minutes did not cause significant changes in ECD or intraoperative or early postoperative complications. None patient lost a line of CDVA 3 months after the procedure.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned.

Objective assessment of the corneal endothelium in Fuchs' endothelial dystrophy

PURPOSE

To develop a standardized method of endothelial cell density (ECD) assessment in Fuchs' endothelial dystrophy that maximizes the sample area and uses the clearest endothelial cells in confocal images.

METHODS

The corneal endothelium of 51 eyes from 30 patients, with varying degrees of Fuchs' endothelial dystrophy, was examined using confocal microscopy. In two or three distinct images of the central endothelium, local contiguous cell density was determined using a variable frame method. The effective ECD was the product of the local cell density and the fraction of the image that was free of guttae. Two examiners assessed the severity of disease in each eye during slit-lamp examination and assigned a severity grade of 1 to 6. In a second group of 55 eyes with Fuchs' dystrophy from 30 patients, the clinical grade was predicted from the effective ECD and the regression coefficients of the first group and compared to the subjective clinical grade assigned by one examiner.

RESULTS

The effective ECD decreased linearly with subjective grade (r = -0.93, P < 0.001). The grade predicted from the effective ECD differed from the subjective clinical grade by -0.1 ± 0.8 (mean difference ± standard deviation).

CONCLUSIONS

The effective ECD in confocal images provides an objective means of assessing the corneal endothelium in Fuchs' dystrophy and might be a useful tool in clinical studies.

Cellular and subbasal nerve alterations in early stage Fuchs' endothelial corneal dystrophy: an in vivo confocal microscopy study

PURPOSE

To analyze the morphology and density of corneal epithelial cells, keratocytes, and subbasal nerves, in patients with early stage Fuchs' endothelial corneal dystrophy (FECD) by in vivo confocal microscopy (IVCM).

METHODS

IVCM (Confoscan 4, Nidek, Inc.) of the central cornea was performed in 30 corneas of 30 patients with early stage FECD and 13 corneas of 13 normal controls. Images were analyzed for morphology and density of the superficial and basal epithelial cells, keratocyte density, endothelial cell density (ECD), as well as subbasal corneal nerve parameters. Central corneal thickness (CCT) was measured in all patients and normals by ultrasound pachymetry.

RESULTS

The ECD was significantly lower (-45.5%, P<0.001) in FECD patients as compared with controls. Total number of nerves and main nerve trunks were significantly reduced (-46.3%, P<0.001; -39.7%, P<0.001) in patients with FECD. Posterior keratocyte density was significantly higher in FECD patients (P<0.001). Significant inverse correlations were found between CCT and total number of nerves (r=-0.69, P<0.001), CCT and main nerve trunks (-0.47, P=0.016), as well as CCT and total nerve length (r=-0.62, P=0.006). Significant correlation was found between ECD and total number of nerves (r=0.44, P=0.012) as well as between ECD and main nerve trunks (r=0.65, P<0.001).

CONCLUSIONS

IVCM demonstrates alterations in corneal innervation in patients with early stage FECD, suggesting a potential role of corneal nerves in the pathogenesis of FECD. Additional studies are required to investigate whether subbasal nerve alterations are caused by nonspecific corneal edema, from FECD-induced decrease in ECD, or potentially leading to loss of endothelial cells.

[Role of in vivo confocal microscopy in irido-corneo-endothelial syndromes]

INTRODUCTION

In vivo confocal microscopy (IVCM) is an increasingly utilized tool in studying complex corneal and anterior segment pathologies. We illustrate the role of this imaging technique in the irido-corneo-endothelial (ICE) syndromes through a case report.

CASE REPORT

A 47-year-old woman presented unilateral decreased vision associated with ocular hypertension and peripheral anterior synechiae. Slit lamp examination of the cornea was unremarkable but IVCM showed pleomorphism and polymegathism of the corneal endothelium and highly reflective nuclei resulting in an epithelial-like cell morphology. This appearance led to the diagnosis of ICE syndrome.

DISCUSSION

Confocal microscopic findings in ICE syndromes are similar to histopathologic findings. This technique may be for a useful diagnostic adjunct in ICE syndromes by revealing specific characteristics, particularly in difficult diagnostic situations, such as when corneal edema impedes specular microscopy or when the iris fails to demonstrate pathognomonic anomalies.

Comparison between laser scanning in vivo confocal microscopy and noncontact specular microscopy in assessing corneal endothelial cell density and central corneal thickness

PURPOSE

To compare central corneal thickness (CCT) and endothelial cell density (ECD) with laser scanning confocal microscope Heidelberg Retina Tomograph (HRT) II Rostock Corneal Module and noncontact specular microscope Tomey EM-3000 and to assess intra- and interobserver agreement in normal corneas.

METHODS

This prospective study included 48 normals (69.6 ± 7.2 years, range: 55-80 years) who underwent CCT and ECD with both Tomey and HRT 3 times by 2 independent observers. Measurement differences between instruments, agreement between devices, and test-retest variability (TRV) were determined.

RESULTS

Mean CCTs with Tomey and HRT were 529.4 ± 35.4 and 536 ± 37.6 μm (P = 0.06), respectively; average ECDs with Tomey and HRT were 2473.5 ± 242.2 and 2539.7 ± 338.6 cells per square millimeter (P = 0.04), respectively. The mean of the differences (HRT minus Tomey) was 6.5 ± 17 μm for CCT and 65 ± 135.1 cells per square millimeter for ECD. Differences between instruments were not related to CCT (P = 0.35), whereas significantly increased with increasing ECD (P = 0.0001). Intraexaminer TRV for Tomey and HRT were 3.9 ± 3.7 and 22.2 ± 18.4 μm for CCT and 73 ± 63.4 and 152.2 ± 148.4 cells per square millimeter for ECD, respectively; interexaminer TRV was 4.6 ± 4.2 and 23.8 ± 17.3 μm for CCT and 84.9 ± 72.3 and 159.8 ± 149.8 cells per square millimeter for ECD.

CONCLUSIONS

HRT II Rostock Corneal Module and the Tomey EM-3000 showed an overall good intermethod agreement. HRT showed a tendency to slightly overestimate CCT measurements, significantly underestimate ECD measurements in eyes with a reduced cell density (< 2290 cells per square millimeter), and overestimate ECD in eyes with a high cell density. Both instruments showed low intra- and interobserver TRV for both CCT and ECD measurements, which tended to be less for Tomey.

In vivo confocal microscopy of the corneal endothelium: comparison of three morphometry methods after corneal transplantation

PURPOSE

The purpose of this study was to assess the endothelium of corneal grafts by in vivo confocal microscopy (IVCM), and to evaluate an automated endothelial software system in comparison with a manual cell count and planimetry.

PATIENTS AND METHODS

Overall, 40 corneal grafts (20 deep anterior lamellar keratoplasties (DALKs) and 20 penetrating keratoplasties (PKs)) were assessed by scanning-slit IVCM. The endothelial cell density (ECD) was estimated with the automated and the manual cell count method of the instrument's Nidek Advanced Vision Information System (NAVIS) software. The results were compared with planimetry as the reference method, and the agreement was assessed.

RESULTS

The mean (±SD) automated ECD was 2278±524 cells/mm(2) (range 1167-3192 cells/mm(2)), whereas the manual cell count method gave significantly lower ECDs with a mean of 1213±677 cells/mm(2) (range 218-2440 cells/mm(2); P<0.001). The manual cell counts were also significantly lower than those by planimetry, with a mean ECD of 1617±813 cells/mm(2) (range 336-2941, P<0.001). Bland-Altman analyses indicated that the limits of agreement (LoA) between the automated and the planimetry method were -671 and +1992 cells/mm(2), whereas they were -1000 and +202 cells/mm(2) when comparing the manual cell counts with planimetry.

CONCLUSION

Following keratoplasty, the NAVIS automated method is likely to overestimate endothelial cell counts due to oversegmenting of the cell domains. Automated ECDs are substantially higher than those by the manual counting method or planimetry. The differences are considerably larger post-keratoplasty than for normal corneas, and the methods should not be used interchangeably.

Corneal nerve aberrations in bullous keratopathy

PURPOSE

To study the corneal nerves in patients with chronic bullous keratopathy.

DESIGN

Prospective observational case series with histologic evaluation.

METHODS

We studied 25 eyes of 25 bullous keratopathy patients of different etiologies (17 female, 8 male; mean age, 76.3 years) as well as 6 eyes of 6 normal control subjects (5 male, 1 female; mean age, 38 years). All subjects were scanned by laser scanning confocal microscope. Five corneal buttons obtained following penetrating keratoplasty from 5 of the above patients and 6 normal control corneal buttons were stained as whole mounts with acetylcholinesterase (AChE) method for corneal nerve demonstration and scanned in multiple layers with digital pathology scanning microscope.

RESULTS

The density, branching pattern, and diameter of sub-basal nerves were significantly lower in corneas with bullous keratopathy compared with normal corneas (density: 4.42 ± 1.91 mm/mm(2) vs 20.05 ± 4.24 mm/mm(2); branching pattern: 36.02% ± 26.57% vs 70.79% ± 10.53%; diameter: 3.07 ± 0.64 μm vs 4.57 ± 1.12 μm). Aberrations such as localized thickenings or excrescences, abnormal twisting, coiling, and looping of the (mid) stromal nerves were observed in the study group both by in vivo confocal microscopy and on histology.

CONCLUSIONS

Striking alterations in corneal innervation are present in corneas with bullous keratopathy that are unrelated to any specific etiology of bullous keratopathy. This study provides histologic confirmation of novel in vivo confocal microscopy findings related to corneal nerves in bullous keratopathy.

Evaluation of a recently developed noncontact specular microscope in comparison with conventional pachymetry devices

PURPOSE

The study was conducted to assess the central corneal thickness (CCT) of the healthy cornea with a recently developed noncontact specular microscope (EM-3000; Tomey) and compare the results with those measured with a contact specular microscope and an ultrasound pachymeter. Agreement between measurements taken by 2 investigators was also studied.

METHODS

The right eyes of 41 healthy individuals who had negative history of contact lens wear, ophthalmic disease, or ocular surgery were examined. The CCT was determined sequentially with a noncontact specular microscope, a contact specular microscope (EM-1000; Tomey), and an ultrasound pachymeter (AL-2000; Tomey). Each evaluation with the specular microscopes was performed by 2 independent operators.

RESULTS

A significant difference was detected in pachymetry measurements among the 3 instruments (p=0.01; analysis of variance). The mean CCT values were lower measured with the ultrasound pachymeter (537+/-30 microm) than the contact endothelial microscope (543+/-37 microm, p=0.17, Student t-test) and the noncontact microscope (549+/-33 microm, p<0.0001) (operator 1). There was no statistically significant difference in CCT measurements between the 2 endothelial microscopes (p=0.19). We found significant correlations (p<0.0001) in thickness measurements between each pair of instruments (r=0.91, noncontact microscopy and ultrasound pachymetry; r=0.74, noncontact and contact microscopy; r=0.72, contact microscopy and ultrasound pachymetry; Spearman rank correlation).

CONCLUSIONS

The strong correlations among the 3 pachymetry devices suggest that the tested instruments provide reliable measurements; however, they cannot be used interchangeably.

Fuchs' corneal dystrophy

Fuchs' corneal dystrophy (FCD) is a progressive, hereditary disease of the cornea first described a century ago by the Austrian ophthalmologist Ernst Fuchs. Patients often present in the fifth to sixth decade of life with blurry morning vision that increases in duration as the disease progresses. Primarily a condition of the posterior cornea, characteristic features include the formation of focal excrescences of Descemet membrane termed 'guttae', loss of endothelial cell density and end-stage disease manifested by corneal edema and the formation of epithelial bullae. Recent advances in our understanding of the genetic and pathophysiological mechanisms of the disease, as well as the application of new imaging modalities and less invasive surgical procedures, present new opportunities for improved outcomes among patients with FCD.

In vivo fluorescence mode confocal microscopy of subepithelial tissues in glaucoma filtering blebs

BACKGROUND AND OBJECTIVE

The miniaturization of confocal imaging technology has resulted in the development of a handheld confocal microscope probe capable of fluorescence mode imaging. Findings in the subepithelial tissues of glaucoma filtering blebs using this novel approach for proof of concept are described.

PATIENTS AND METHODS

A fiberoptic confocal imaging probe using an illumination wavelength of 488 nm was applied to the bleb surface of 11 eyes after topical or subconjunctival administration of sodium fluorescein. The imaging plane was moved to the subepithelial region and multiple images from multiple bleb regions were captured at a resolution of 1,024 x 1,024 pixels per square inch.

RESULTS

High-quality images of the bleb wall structure, vasculature, and superficial sclera were obtained and demonstrated subcellular detail. Lateral resolution was between 1 and 1.5 microm and axial resolution was approximately 30 microm. Identifiable structures in the failing blebs included vasculature (including individual erythrocytes, pericytes, and vascular endothelium); microcystic structures; and cells within the Tenon's tissue, some of which resembled fibroblasts.

CONCLUSION

Fluorescence mode imaging of ocular subsurface detail is a viable and promising tool for assessment of wound healing and other processes in trabeculectomy blebs. The ability to image fluorophores creates the possibility of functional imaging.

Corneal endothelium in patients with diabetes mellitus: a historical cohort study

PURPOSE

Retinopathy is the major cause of ocular morbidity in patients with diabetes mellitus. Chronic hyperglycemia spares no organ and can affect the morphology and function of the various corneal layers, compromising its transparency. This study was conducted to associate the status of corneal endothelium to diabetes mellitus (DM) and identify risk factors of compromised corneal endothelium.

METHODS

A total of 220 eyes of randomly selected patients (110 diabetic and 110 nondiabetic) were subjected to detailed slitlamp and fundus evaluation. Corneal endothelial status was evaluated using the Nidek Confoscan 2. Cell density, percentage polymegathism, and pleomorphism were calculated. The findings in diabetic patients were compared to those without disease. The outcome was correlated to diabetic retinopathy (DR). The effects of hypertension, hyperlipidemia, age, gender, type, duration, glycemic control, and grades of DR was also considered.

RESULTS

The mean corneal endothelial cell density was -175 cells/mm2 (95% CI -317 to -33 cells/mm2) less in eyes of diabetic patients. The number of endothelial cells with polymegathism was significantly greater among eyes of diabetic patients. There were less corneal endothelial cells with pleomorphism in nondiabetic patients. Polymegathism and pleomorphism of corneal endothelial cells seems to be positively associated with DM type II. Cell density was significantly lower in eyes with DR than those without DR.

CONCLUSIONS

Corneal endothelium in diabetic patients seems to be compromised. Evaluation of corneal endothelium should be part of protocol for eye care of diabetic patients.

A comparison of two methods for estimating polymegethism in cell areas of the human corneal endothelium

PURPOSE

To compare the outcome measures from two different methods for estimating the coefficient of variation (COV) in cell area for human corneal endothelia.

METHODS

A single non-contact specular micrograph was obtained from the central region of the corneal endothelium of 100 healthy non-contact lens-wearing white European subjects, aged from 32 to 62 years. The captured image file was either assessed using a machine-based algorithm in which 21 cells were marked and their areas reported (designated as the TOPCON 'centre-dot' method), or by an overlay and semi-automated computer-based image analysis system of the entire image of around 200 cells (designated as the AUTO method). The average cell area values were used to calculate the endothelial cell density (ECD), while the COV was calculated from the standard deviation of the cell area measures.

RESULTS

The TOPCON and AUTO methods yielded comparable data for average cell area (395 vs 391 microm(2)) and estimated ECD (2566 vs 2575 cells mm(-2)) that were not statistically different (p > or = 0.351), although there was a slight bias between the two methods. However, the mean COV values were very different at 43.5 and 31.4% (p < 0.001). The overestimation of the COV was related to the difference in the largest cell area domain identified by the two methods (p < 0.001, r = > or =0.748).

CONCLUSIONS

A centre-dot method using a small number of cells generates useful data on cell area and ECD, but it should be used cautiously for estimates of COV.

Could the coefficient of variation (COV) of the corneal endothelium be overestimated when a centre-dot method is used?

BACKGROUND

Little has been published on the reliability of estimates of the coefficient of variation (COV) in cell area for human corneal endothelia. The present study compares two methods.

METHODS

A non-contact specular micrograph (Topcon SP-2000P) was obtained from the central region of the corneal endothelium of 20 healthy myopic white European subjects, aged from 32 to 53 years, half of whom were successful long-term soft contact lens wearers. The captured image file was either assessed using a machine-based algorithm, in which 25 cells in the middle of the image were marked and their areas reported (designated as 'centre-dot' method) or by a manual method, by which all the cells in the image were outlined on very high magnification prints of the endothelia and the cell areas measured by a manual digitiser in stream mode. The average cell area was used to calculate the endothelial cell density (ECD), while the COV was calculated from the standard deviation (SD) of the cell area measures.

RESULTS

Identical mean cell area values were found (392 microm(2)) with the two methods, a marginally higher ECD estimate (2,594 versus 2,569) with the centre-dot method (p = NS) but a much higher COV with the centre-dot method (43.8 versus 29.0 per cent). This highly statistically significant difference in COV (p < 0.001) was seen in both contact lens wearers and non-contact lens wearers. A Bland-Altman analysis reveals a bias in the centre-dot method, especially for the COV estimates, that appears to be linked to erroneous definition of a single large cell domain on any individual image.

CONCLUSIONS

A centre-dot method can be reliably used to generate useful data on cell area and ECD but it should be used cautiously for estimates of polymegethism (COV).