Correlation of histologic corneal endothelial cell counts with specular microscopic cell density

Enhanced Migration of Fuchs Corneal Endothelial Cells by Rho Kinase Inhibition: A Novel Ex Vivo Descemet's Stripping Only Model

Descemet's Stripping Only (DSO) is a surgical technique that utilizes the peripheral corneal endothelial cell (CEnC) migration for wound closure. Ripasudil, a Rho-associated protein kinase (ROCK) inhibitor, has shown potential in DSO treatment; however, its mechanism in promoting CEnC migration remains unclear. We observed that ripasudil-treated immortalized normal and Fuchs endothelial corneal dystrophy (FECD) cells exhibited significantly enhanced migration and wound healing, particularly effective in FECD cells. Ripasudil upregulated mRNA expression of Snail Family Transcriptional Repressor (SNAI1/2) and Vimentin (VIM) while decreasing Cadherin (CDH1), indicating endothelial-to-mesenchymal transition (EMT) activation. Ripasudil activated Rac1, driving the actin-related protein complex (ARPC2) to the leading edge, facilitating enhanced migration. Ex vivo studies on cadaveric and FECD Descemet's membrane (DM) showed increased migration and proliferation of CEnCs after ripasudil treatment. An ex vivo DSO model demonstrated enhanced migration from the DM to the stroma with ripasudil. Coating small incision lenticule extraction (SMILE) tissues with an FNC coating mix and treating the cells in conjunction with ripasudil further improved migration and resulted in a monolayer formation, as detected by the ZO-1 junctional marker, thereby leading to the reduction in EMT. In conclusion, ripasudil effectively enhanced cellular migration, particularly in a novel ex vivo DSO model, when the stromal microenvironment was modulated. This suggests ripasudil as a promising adjuvant for DSO treatment, highlighting its potential clinical significance.

The Effect of Mesenchymal Stem Cell Secretome on Corneal Endothelial Cell Preservation in an Oxidative Injury Model

PURPOSE

To describe a reproducible oxidative injury model in ex vivo porcine corneas and to investigate the effects of corneal mesenchymal stem cell (Co-MSC) secretome and specific factors on the preservation of corneal endothelium after oxidative injury.

METHODS

Porcine corneas underwent vital staining with trypan blue and alizarin red with different concentration and time points. Ex vivo porcine corneas were exposed (endothelial side) to varied concentrations of hydrogen peroxide. After injury, 3 groups of 5 corneas underwent treatment with secretome from either a wild-type (WT) murine Co-MSC, a pigment epithelium derived factor (PEDF) knock out (K/O) murine Co-MSC, or basal media for 4 hours at 37°C. The viability of the endothelium was evaluated using the optimized vital staining protocol.

RESULTS

The optimal vital staining was achieved with 0.4% trypan blue for 60 seconds and 0.5% alizarin red for 90 seconds. The optimal oxidative injury (for consistency and level of damage) was obtained with 1% hydrogen peroxide for 15 seconds. Treatment with both WT Co-MSC and PEDF K/O Co-MSC secretome significantly reduced the endothelial damage compared with control (17.2% ± 10.0%, 33.5% ± 11.6%, and 68% ± 17%, respectively, P < 0.01). The WT Co-MSC secretome was significantly more effective compared with PEDF K/O Co-MSC secretome (P < 0.05).

CONCLUSIONS

A reproducible model of vital staining and oxidative injury is described for studying porcine corneal endothelial survival. Our results demonstrate a beneficial role of a corneal MSC secretome in reducing oxidative damage to the corneal endothelium. In addition, it suggests a potential role for PEDF in this process.

Agreement of Corneal Endothelial Cell Analysis Between Konan-Noncon Robo SP-6000 and Tomey EM-3000 Specular Microscopes in Healthy Subjects

PURPOSE

To compare corneal endothelium parameters taken by two common noncontact specular microscopes in healthy subjects.

METHODS

Healthy participants visiting the outpatient eye clinic at the Rabin Medical Center, Petah Tikva, Israel, were recruited prospectively. All participants underwent three consecutive corneal endothelial cell photographs with both the Konan-Noncon Robo SP-6000 and the Tomey EM-3000 specular microscopes. Endothelial cell density (ECD) was evaluated using the manual center technique in both machines. Bland-Altman graphs were used to assess the agreement between the devices, and intraclass correlation coefficient (ICC) served to assess intraobserver variability for each device.

RESULTS

Recruited were 49 healthy subjects with a mean age of 48.9±15.6 years, 49 right eyes were included. The mean ECD was comparable between the Tomey EM-3000 and the Konan-Noncon Robo SP-6000 (2,713.2±242.4 vs. 2,700.8±300.5 cells/mm2, respectively, P=0.47) with a mean difference of 12.4 cells/mm2 (0.67%), a mean ECD absolute difference of 93.3 cells/mm2, and low 95% limits of agreement of -222.0 to +246.9 cells/mm2. A folded empirical distribution function curve showed that all differences fell within 525.4 cells/mm2, centered around a median of 13.3 cells/mm2. Intraclass correlation coefficient was high for both the Konan-Noncon Robo SP-6000 (0.93, 95% confidence interval [CI]: 0.89-0.95) and the Tomey EM-3000 (0.88, 95% CI: 0.82-0.93).

CONCLUSIONS

The difference in endothelial cell measurements between the Konan SP-6000 and the Tomey EM-3000 specular microscopes through the center and the L-count analyzing techniques, respectively, is clinically small and not statistically significant. Nevertheless, caution should be taken when used interchangeably because ECD difference between the two machines can be as high as 525.4 cells/mm2.

Increased Corneal Endothelial Cell Migration in Fuchs Endothelial Corneal Dystrophy: A Live Cell Imaging Study

Purpose

To investigate if corneal endothelial cells (CECs) in Fuchs endothelial corneal dystrophy (FECD) have altered cellular migration compared with normal controls.

Design

Comparative analysis.

Materials

Descemet's membrane and CECs derived from patients with FECD undergoing endothelial keratoplasty or normal cadaveric donors.

Methods

Ex vivo specimens were used for live cell imaging and generation of immortalized cell lines. Live imaging was performed on FECD and normal CECs and on ex vivo specimens transfected with green fluorescent protein. Migration speeds were determined as a function of cellular density using automated cell tracking. Ex vivo specimens were classified as either FECD or normal low cell density (nonconfluent) or high cell density (confluent). Scratch assay was performed on CECs seeded at high confluence to determine migration speed. Genetic analysis from blood samples or CECs was performed to detect a CTG repeat expansion in the TCF4 gene.

Main Outcome Measures

Mean cell migration speed.

Results

Fuchs endothelial corneal dystrophy CECs in low cell density areas displayed increased mean speed (0.391 ± 0.005 μm/minute vs. 0.364 ± 0.005 μm/minute; P < 0.001) and mean maximum speed (0.961 ± 0.010 μm/minute vs. 0.787 ± 0.011 μm/minute; P < 0.001) compared with normal CECs, and increased mean maximum speed (0.778 ± 0.014 μm/minute vs. 0.680 ± 0.011 μm/minute; P < 0.001) in high cell density areas ex vivo. Similarly, FECD CECs displayed increased mean speed compared with normal CECs (1.958 ± 0.020 μm/minute vs. 2.227 ± 0.021 μm/minute vs. 1.567 ± 0.019 μm/minute; P < 0.001) under nonconfluent conditions in vitro. Moreover, FECD CECs also displayed increased mean speed compared with normal CECs under high confluent conditions as detected by scratch assay (37.2 ± 1.1% vs. 44.3 ± 4.1% vs. 70.7 ± 5.2%; P < 0.001). Morphologic analysis showed that FECD CECs displayed an increased fibroblastic phenotype as detected by filamentous-actin labeling.

Conclusions

Fuchs endothelial corneal dystrophy CECs demonstrated increased migration speed compared with normal CECs. Further investigation into the mechanisms of heightened cell migration in FECD is needed and may provide insight into its pathogenesis, as well as having implications on descemetorhexis without endothelial keratoplasty.

Comparative Evaluation of Corneal Endothelium in Patients with Diabetes Undergoing Phacoemulsification

PURPOSE

The purpose of this study is to determine if phacoemulsification with posterior chamber foldable intraocular lens implantation has a greater impact on the corneal endothelium of type 2 diabetic patients as compared to nondiabetic controls.

MATERIALS AND METHODS

This study compared the corneal endothelial status in sixty patients with diabetes with good glycemic control and sixty nondiabetic controls before and after (1 week, 1 month, 2 month, and 3 month) uneventful phacoemulsification. Central corneal endothelial cell density, percentage hexagonality, and coefficient of variation were measured using a noncontact specular microscope. Central corneal thickness was taken as a surrogate marker for endothelium functional status.

RESULTS

Data were age and sex matched. Patients with diabetes showed significantly higher loss in endothelial cell count as compared to nondiabetic controls. Furthermore, the patients with diabetes showed a slower recovery trend in the endothelial healing response as evidenced by lower change in the coefficient of variation. Significant correlation was found between energy used and change in endothelial count as well as coefficient of variation in nondiabetics only.

CONCLUSION

In spite of good glycemic control, patients with diabetes have significantly more endothelial damage in comparison to nondiabetic controls with similar nuclear grading and phaco energy used. This warrants a more careful use of phaco energy in patient with diabetes.

Connection of histological corneal endothelial cell count with endothelial cell density before penetrating keratoplasty

PURPOSE

Corneal endothelial cell density and the integrity of the monolayer are essential for maintenance of a clear cornea. In 1992, Williams et al. introduced a method to estimate the endothelial cell density in histopathologic examination. It would enable an evaluation of the corneal host endothelium, even if preoperative measurement was not possible. The goal of this study is to evaluate the accuracy of the Williams equation in corneal buttons obtained from penetrating keratoplasties.

METHODS

High power field (HPF) photographs and histological endothelial cell counts were made from the corneal endothelial cells of each corneal histopathological cross-section. We then compared the calculated endothelial cell density using the Williams equation with the preoperative measured endothelial cell density. A bivariate regression analysis of the histological HPF cell counts and the preoperative endothelial cell density count was also performed.

RESULTS

The equation of Williams et al. overestimates the endothelial density in all of our patients. Linear regression showed a strong relation between the central histological HPF count and the preoperative endothelial cell density. The regression formula for the endothelial cell density is 59.66 + (272.447 × HPF count); p < 0.001, R ² = 0.901.

CONCLUSION

This study confirms the relation between the corneal endothelial cell density, measured with specular microscopy, and the histopathological endothelial cell count in a HPF. However, the equation of Williams et al. provides an overestimation of the endothelial cell density. To proper utilize the histopathological endothelial cell count, a calibration of the equation coefficients in the local setting is necessary to prevent systematic errors.

One hundred-year-old human corneal and transplanted corneal graft endothelium

PURPOSE

To investigate and analyse one hundred-year-old endothelial cells of human transplanted corneal grafts and compare them with intact endothelium of unoperated eyes.

SUBJECTS AND METHODS

Specular microscopy was performed on seven individuals (14 eyes) aged >100 years and on seven transplanted corneas with endothelial cells of at least 100 years old. All keratoplasties were performed by the same surgeon (PR) 25-35 years before the time of examination. As controls, 14 unoperated healthy individuals (26 eyes) of 90-100 years, 12 individuals (24 eyes) of 48-52 years, 12 students (24 eyes) of 19-24 years and 11 children (22 eyes) from 10 to 14 years of age were photographed and analysed.

RESULTS

The mean cell density in the oldest age group, over 100 years of age (average 102 years), was very good 2365 cells/mm(2) . The mean cell density in the transplanted corneas, the endothelial cells of which were over 100 years old (mean 106 years), was 923 cells/mm(2) (range 585-1800 cells/mm(2) ).

CONCLUSION

Corneal endothelial cells may remain viable and capable to perform their function over 100 years. Donor corneas up to 70-75 years of age can be approved for transplantation, provided that the endothelial cells have been thoroughly evaluated with vital staining before the operation.

Propagation of Human Corneal Endothelial Cells: A Novel Dual Media Approach

Corneal endothelium-associated corneal blindness is the most common indication for corneal transplantation. Restorative corneal transplant surgery is the only option to reverse the blindness, but a global shortage of donor material remains an issue. There are immense clinical interests in the development of alternative treatment strategies to alleviate current reliance on donor materials. For such endeavors, ex vivo propagation of human corneal endothelial cells (hCECs) is required, but current methodology lacks consistency, with expanded hCECs losing cellular morphology to a mesenchymal-like transformation. In this study, we describe a novel dual media culture approach for the in vitro expansion of primary hCECs. Initial characterization included analysis of growth dynamics of hCECs grown in either proliferative (M4) or maintenance (M5) medium. Subsequent comparisons were performed on isolated hCECs cultured in M4 alone against cells expanded using the dual media approach. Further characterizations were performed using immunocytochemistry, quantitative real-time PCR, and gene expression microarray. At the third passage, results showed that hCECs propagated using the dual media approach were homogeneous in appearance, retained their unique polygonal cellular morphology, and expressed higher levels of corneal endothelium-associated markers in comparison to hCECs cultured in M4 alone, which were heterogeneous and fibroblastic in appearance. Finally, for hCECs cultured using the dual media approach, global gene expression and pathway analysis between confluent hCECs before and after 7-day exposure to M5 exhibited differential gene expression associated predominately with cell proliferation and wound healing. These findings showed that the propagation of primary hCECs using the novel dual media approach presented in this study is a consistent method to obtain bona fide hCECs. This, in turn, will elicit greater confidence in facilitating downstream development of alternative corneal endothelium replacement using tissue-engineered graft materials or cell injection therapy.

Corneal changes in xeroderma pigmentosum: a clinicopathologic report

PURPOSE

To report the clinicopathologic features of corneal involvement in patients with xeroderma pigmentosum.

DESIGN

Retrospective review of corneal histopathology.

METHODS

Thirteen corneal specimens of 11 patients with xeroderma pigmentosum who underwent keratoplasty (lamellar/full-thickness) for corneal involvement were studied. Five-micrometer-thick sections were made from all the samples and stained using hematoxylin-eosin and periodic acid-Schiff stains. A light microscopic examination was performed to study the histopathologic changes.

RESULTS

The corneal findings on clinical examination were haze, scarring, vascularization, stromal edema, pigment clumps on endothelial surface, and corneal thinning. The histopathologic evaluation revealed changes in all layers of cornea. Epithelial changes seen were intraepithelial edema, fibrosis, epithelial downgrowths, and pannus formation. The Bowman membrane was fragmented or absent. Stroma was characterized by alteration in the lamellar pattern, scarring, edema, loss of keratocytic nuclei, and calcification. The Descemet membrane was thickened to a variable extent in most specimens and there was marked loss of endothelial cells in all.

CONCLUSION

Most histologic features are consistent with the previous few reports. The remarkable finding in all corneal specimens was a moderate to severe degree of loss of the endothelial cells. This noteworthy finding supports the ultraviolet (UV) radiation-induced endothelial cell damage in these patients. This has an important clinical implication when planning for anterior lamellar keratoplasty, as endothelial cell density may be subnormal in these patients.

Anatomic alterations in aging and age-related diseases of the eye

PURPOSE

We described anatomic age-related changes in the human eye to determine potential areas of investigation that may lead to identifying eyes at risk for age-related disease.

METHODS

A descriptive review of anatomic changes in the eye related to aging was performed in the context of current areas of investigation. The review was performed specifically for differing anatomic ocular structures, including cornea, trabecular meshwork, lens, uveal tract, Bruch's membrane, retina, RPE, vitreous, sclera, and optic nerve.

RESULTS

Age-related changes occur in all ocular tissues. The cornea flattens and there is an attrition of endothelial cells. The shape of the trabecular meshwork changes and there is a loss of trabecular endothelium. The lens grows and becomes cataractous. The ciliary body becomes collagenized, there are choroidal vascular changes, and Bruch's membrane thickens. Retinal vessels become hyalinized and there is a loss of rods before cones in the macula. RPE morphometric changes occur with aging. The vitreous becomes liquefied and there is a loss of vitreous compartmentalization. The sclera becomes rigid and may become calcified. The optic nerve exhibits structural changes with age.

CONCLUSIONS

There are numerous anatomic age-related changes in the human eye. Current areas of investigation related to these changes include adaptive optics scanning laser ophthalmoscopy imaging of the RPE mosaic in the context of aging, and drug delivery devices that overcome age-related alterations to retinal and macular perfusion.

The culture of limbal stromal cells and corneal endothelial cells

The cornea is the transparent front part of the eye and comprises three distinct cell layers. One of these cell layers is a self-renewing epithelium long believed to harbor a resident stem cell population. The location and characteristics of corneal epithelial stem cells have now been confirmed by several research groups, and these cells are currently applied therapeutically. The corneal stroma and endothelium are largely quiescent after infancy, and until recently they were not considered to undergo self-renewal or to maintain stem cells. This view was overturned during the last two decades. At present, cell populations with characteristics of adult stem cells are routinely isolated and characterized from the limbal stroma and the corneal -endothelium. This chapter describes methods for isolation and culture of limbal stromal cells and corneal endothelial cells.

Optimization of human corneal endothelial cells for culture: the removal of corneal stromal fibroblast contamination using magnetic cell separation

The culture of human corneal endothelial cells (CECs) is critical for the development of suitable graft alternative on biodegradable material, specifically for endothelial keratoplasty, which can potentially alleviate the global shortage of transplant-grade donor corneas available. However, the propagation of slow proliferative CECs in vitro can be hindered by rapid growing stromal corneal fibroblasts (CSFs) that may be coisolated in some cases. The purpose of this study was to evaluate a strategy using magnetic cell separation (MACS) technique to deplete the contaminating CSFs from CEC cultures using antifibroblast magnetic microbeads. Separated "labeled" and "flow-through" cell fractions were collected separately, cultured, and morphologically assessed. Cells from the "flow-through" fraction displayed compact polygonal morphology and expressed Na(+)/K(+)ATPase indicative of corneal endothelial cells, whilst cells from the "labeled" fraction were mostly elongated and fibroblastic. A separation efficacy of 96.88% was observed. Hence, MACS technique can be useful in the depletion of contaminating CSFs from within a culture of CECs.

Toxicity comparison of intraocular azithromycin with and without a bioadhesive delivery system in rabbit eyes

PURPOSE

To determine whether the addition of a bioadhesive drug-delivery system to topical azithromycin induces intraocular inflammation and damage when introduced intraocularly by different approaches and in varying doses.

SETTING

John A. Moran Eye Center, Salt Lake City, Utah, USA.

DESIGN

Experimental study.

METHODS

Commercial topical azithromycin 1.0% was duplicated, including the benzalkonium chloride, but without inclusion of the Durasite bioadhesive drug-delivery system. Injections of 50 μL, 25 μL, and 10 μL of the antibiotic solutions were administered in a masked fashion to 2 rabbits; 1 eye (study eye) in each rabbit was randomized to receive azithromycin with the delivery system and the fellow eye (control eye) to receive azithromycin without the delivery system. Two rabbits had topical drops of each solution placed after a 2.8 mm incision was created. Masked slitlamp examinations, pachymetry, and intraocular pressure (IOP) were determined 1 day and 2 days postoperatively. The animals were humanely killed, and the endothelial density and histopathology were examined.

RESULTS

The IOP (P<.001), pachymetry (P<.001), and signs of inflammation (P=.38 to .003) were consistently higher in the study eye, especially at the 50 μL dose, than in the control eye. This was confirmed by histopathology.

CONCLUSION

If the drug-delivery system gains access to the anterior chamber, it may cause substantial corneal edema and inflammation, even at low doses and after topical administration.

Human corneal endothelial cell expansion for corneal endothelium transplantation: an overview

The monolayer of cells forming the human corneal endothelium is critical to the maintenance of corneal transparency and is not known to regenerate in vivo. Thus, dysfunction of these cells constitutes the most often cited reasons for the 150,000 or so corneal transplants performed yearly. Although current corneal transplantation is more than 90% successful at 1 year, longer term results are not as encouraging with approximately 70% success at 5 years. Nonimmunologic graft failure and allograft endothelial rejection are the main problems. Furthermore, the global shortage of donor corneas greatly restricts several corneal transplantations performed. With advances in understanding corneal endothelial cell biology, it is now possible to cultivate human corneal endothelial cells (HCECs) in vitro, thus providing new opportunities to develop novel tissue-engineered human corneal endothelium. This review will provide an overview of (a) the characteristics of human corneal endothelium; (b) past and present HCECs isolation and culture protocols; (c) various potential carriers for the generation of tissue-engineered corneal endothelium, together with some of the functional studies reported in various animal models; and (d) the current rapid advancements in surgical techniques for keratoplasty. A successful combination of tissue-engineered human corneal endothelium coupled with innovative and groundbreaking surgical procedures will bridge basic research involving cultured HCECs, bringing it from bench to bedside.

An anterior chamber toxicity study evaluating Besivance, AzaSite, and Ciprofloxacin

PURPOSE

We determined whether Besivance (Bausch & Lomb), AzaSite (Inspire Pharmaceuticals, Inc; both with DuraSite bioadhesive [InSite Vision, Inc]) and ciprofloxacin are toxic inside the anterior chamber.

DESIGN

Randomized, masked, placebo-controlled animal study.

METHODS

Twenty New Zealand white rabbits (40 eyes) were randomized to 1 of 4 study groups: Besivance, AzaSite, ciprofloxacin, and balanced salt solution. Each eye was injected with 0.1 mL of the study medication. Clinical slit-lamp examinations were conducted at 24 and 48 hours after injection. All rabbits then were killed and all eyes were enucleated. We randomized eyes to either corneal vital staining or histopathologic examination. The main outcome measures were clinical and pathologic signs of toxicity.

RESULTS

The 2 DuraSite-based study groups (Besivance and AzaSite) showed clinically and pathologically significant differences when compared with the ciprofloxacin and balanced salt solution groups. Besivance and AzaSite eyes exhibited significantly similar and severe clinical damage, including severe corneal edema. Ciprofloxacin and balanced salt solution eyes appeared very similar and had only mild conjunctival injection and limbal vascularity. Vital staining and histopathologic evaluation revealed glaucomatous and toxic damage in eyes given DuraSite-based medications, whereas non-DuraSite groups showed minimal changes.

CONCLUSIONS

DuraSite blocks the trabecular meshwork and may be additionally toxic when introduced as a large bolus. Until the safety of these medications is established with further studies using smaller injected volumes, we recommend placement of a suture over a clear corneal wound if DuraSite-based medications are used.

Clinicopathologic findings in failed descemet stripping automated endothelial keratoplasty

OBJECTIVE

To evaluate the clinical features of and histologic findings from failed Descemet stripping automated endothelial keratoplasty (DSAEK).

METHODS

This retrospective observational case series evaluated 47 consecutive corneal specimens from 42 patients who underwent either penetrating keratoplasty or repeated DSAEK for failed DSAEK. Clinical information was obtained for the cases. Sections of the specimens were examined using light microscopy. Immunohistochemical staining was performed for cytokeratins AE1/AE3 and for the myogenic marker smooth-muscle actin when indicated. Transmission electron microscopic examination was performed in some cases.

RESULTS

Graft survival ranged from 0.5 to 34 months. Histologic examination showed that 94% of the specimens (44 of 47) had endothelial cell loss. Residual host Descemet membrane (19%; 9 of 47), fibrocellular tissue (19%; 9 of 47), epithelial implantation (15%; 7 of 47), and fungal infection (4%; 2 of 47) were also identified. Immunohistochemical stains were positive for AE1/AE3 in the epithelial implantations and for smooth-muscle actin in cells in the fibrocellular proliferations.

CONCLUSIONS

The principal cause of failed DSAEK is endothelial cell loss. Residual host Descemet membrane, fibrocellular tissue at the edge of the lenticule, and epithelial implantation are common histologic findings. Fungal infection may occur in the setting of DSAEK.

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.

Corneal endothelial cell morphology of normal dogs in different ages

Endothelial cell function is essential to maintain corneal transparency, but unfortunately the regenerative capacity of the endothelium is limited. There are only a few reports describing the effect of age on morphologic appearance of corneal endothelial cells of dogs. Studies of normal corneal endothelial cells in humans and dogs have shown a decrease in endothelial cell density (ECD) and an increase in pleomorphism and polymegethism with advancing age. The purpose of this study was to investigate the effect of age on ECD and endothelial cell morphology in dogs. A total of 30 dogs were divided into three groups (10 dogs/group) based on age: group 1 (2-12 months old), group 2 (24-72 months old), and group 3 (84 months or older). Corneas were processed for light and scanning electron microscopy. Results showed only difference in cell density between group 1 and groups 2 and 3, showing an initial decrease in cell density as the animal matured. Whereas there was significantly greater variation in cell size within the dogs in group 3 than there was within the other two groups, suggesting that there was increased polymegethism and pleomorphism with advancing age.

Rate of change in central corneal thickness: a viability indicator for conventional drainage tissues in organ culture

Organ culture of human anterior segments is a powerful tool for understanding trabecular meshwork biology. However, data from a significant percentage of cultured anterior segments are unusable because tissues fail to meet quality control requirements, such as having adequate trabecular meshwork histology. The purpose of the present study was to evaluate a novel, real time method for assessing the viability of conventional drainage tissues in the human anterior segment perfusion model. Twenty-two human anterior segments were perfusion cultured using standard techniques for one week while measuring outflow facility and central corneal thickness (CCT). After perfusion-fixation, toludine blue-stained histological sections of drainage tissues from all four quadrants of each anterior segment were graded and endothelial cell nuclei from cornea centers were stained with 4',6-diamidino-2-phenylindole and counted. We found that most anterior segments with a stable outflow facility had a CCT that decreased over time, while anterior segments with an unstable outflow facility had CCT measurements that failed to decrease over time (P<0.01). When comparing CCT measurements to histological appearance of outflow tissues, we found that in 11/11 cases, anterior segments with an acceptable histological score had a negative CCT slope (P<0.01). Conversely in 3/4 instances, anterior segments with an unacceptable histological score had a positive CCT slope. Lastly, we observed a significant relationship between CCT measurements and corneal endothelial density (P<0.01). Thus, the simple procedure of measuring CCT during anterior segment perfusion provides a second useful measure to assess the viability of the anterior segment during the perfusion process.

An evaluation of image quality and accuracy of eye bank measurement of donor cornea endothelial cell density in the Specular Microscopy Ancillary Study

PURPOSE

The Specular Microscopy Ancillary Study was designed to examine donor corneal endothelial specular image quality, compare the central endothelial cell density determined by eye banks with the endothelial cell density determined by a central specular microscopy reading center, and evaluate donor factors that may have an impact on specular image quality and endothelial cell density accuracy.

DESIGN

Nonrandomized comparative trial.

PARTICIPANTS

Endothelial specular images of donor corneas assigned in the Cornea Donor Study.

METHODS

Certified readers assessed donor image quality (analyzable from fair to excellent vs. unanalyzable) and determined the central endothelial cell density. Independent adjudication was performed if there was a difference in the quality of grading or if the endothelial cell density varied by > or =5.0% between readers. Average reading center-determined endothelial cell density was compared with the endothelial cell density determined by each eye bank.

MAIN OUTCOME MEASURES

Evaluation of image quality and accuracy of endothelial cell density.

RESULTS

Of 688 donor endothelial images submitted by 23 eye banks, 663 (96%) were analyzable (excellent, 40 [6%]; good, 302 [44%]; fair, 321 [47%]), and 25 (4%) were unanalyzable by reading center standards. In situ retrieval and greater epithelial exposure correlated with a higher image quality grading. The eye bank-determined endothelial cell density of 434 of the 663 (65%) analyzable images were within 10% of the endothelial cell density determined by the reading center, whereas 185 (28%) were more than 10% higher and 44 (7%) were more than 10% lower. Greater variation in endothelial cell density between the eye banks and the reading center was observed with shorter time of death to preservation, presence of an epithelial defect, folds in Descemet's membrane, lower image quality, and the use of fixed-frame or center method endothelial cell density analysis.

CONCLUSIONS

Overall, donor endothelial specular image quality and accuracy of endothelial cell density determination were good. However, the data suggest that factors that may affect image quality and contribute to variation in interpretation of the endothelial cell density should be addressed, because the donor endothelial cell density is an important parameter for assessing long-term corneal graft survival.

Pathologic findings in postmortem corneas after successful laser in situ keratomileusis

PURPOSE

To examine the histologic and ultrastructural features of human corneas after successful laser in situ keratomileusis (LASIK).

METHODS

Corneas from 48 eyes of 25 postmortem patients were processed for histology and transmission electron microscopy (TEM). The 25 patients had LASIK between 3 months and 7 years prior to death. Evaluation of all 5 layers of the cornea and the LASIK flap interface region was done using routine histology, periodic acid-Schiff (PAS)-stained specimens, toluidine blue-stained thick sections, and TEM.

RESULTS

In patients for whom visual acuity was known, the first postoperative day uncorrected visual acuity was 20/15 to 20/30. In patients for whom clinical records were available, the postoperative corneal topography was normal and clinical examination showed a semicircular ring of haze at the wound margin of the LASIK flap. Histologically, the LASIK flap measured, on average, 142.7 microm (range, 100-200). A spectrum of abnormal histopathologic and ultrastructural findings was present in all corneas. Findings at the flap surface included elongated basal epithelial cells, epithelial hyperplasia, thickening and undulations of the epithelial basement membrane (EBM), and undulations of Bowman's layer. Findings in or adjacent to the wound included collagen lamellar disarray; activated keratocytes; quiescent keratocytes with small vacuoles; epithelial ingrowth; eosinophilic deposits; PAS-positive, electron-dense granular material interspersed with randomly ordered collagen fibrils; increased spacing between collagen fibrils; and widely spaced banded collagen. There was no observable correlation between postoperative intervals and the severity or type of pathologic change except for the accumulation the electron-dense granular material.

CONCLUSIONS

Permanent pathologic changes were present in all post-LASIK corneas. These changes were most prevalent in the lamellar interface wound. These changes along with other pathologic alterations in post-LASIK corneas may change the functionality of the cornea after LASIK.

Long-term histopathologic findings in human corneal wounds after refractive surgical procedures

OBJECTIVE

To describe the human corneal histopathology after laser in situ keratomileusis, photorefractive keratectomy, astigmatic keratoplasty, clear corneal refractive lens surgery, conductive keratoplasty, and intrastromal corneal ring segment placement.

DESIGN

Retrospective histopathologic study and selected literature review.

METHODS

Ninety-four postmortem corneas from 49 patients and 10 corneal button specimens from 6 patients with previous refractive surgery were collected from eye banks and refractive surgeons in North America. This observational case series evaluated the pathologic findings in the wounds of these corneas in the context of previous studies.

RESULTS

Three histopathologic types of corneal wound-healing responses were present in corneas after refractive surgery. The first was an epithelial cell modification that reestablished a smooth anterior corneal surface through basal epithelial cell hypertrophy, by epithelial hyperplasia, or both. The second was the production of a hypercellular fibrotic stromal scar, and the third was the production of a hypocellular primitive stromal scar. Although only the hypercellular fibrotic stromal scar could be identified on gross examination, all three wound responses were identified with light, electron, and immunofluorescence microscopy. Confocal microscopy also identified these three processes but with less detail and resolution.

CONCLUSION

Understanding the locations, clinical appearance, and functional attributes of these wound-healing responses will help guide evolving techniques or adjunctive treatments.

Increased endothelial cell density in the paracentral and peripheral regions of the human cornea

PURPOSE

To systematically investigate the central, paracentral, and peripheral endothelial cell density (ECD) in normal human corneas.

DESIGN

Observational case series and experimental study.

METHODS

Noncontact specular microscopy was undertaken to determine the ECD of the central, paracentral (2.7 +/- 0.2 mm from center) and peripheral (4.7 +/- 0.2 mm from center) regions of the cornea of 48 normal eyes. The ECDs of central and peripheral regions were also determined with contact specular microscopy in 21 normal eyes and a group of 30 Optisol-GS eye bank corneas were evaluated with alizarin red stain. Histologic ECD of 13 Optisol-GS stored corneas were also determined.

RESULTS

Paracentral and peripheral ECD measured with the noncontact specular microscope were 5.8% (P <.01) and 9.6% (P <.001) increased compared with central ECD. Superior peripheral ECD was increased compared with the other three peripheral quadrants (P <.05) and was 15.9% higher than central ECD. Contact specular microscopy showed an increase of 8.9% in the peripheral ECD from the center. Alizarin red stained corneas confirmed the specular microscopy numbers with a 9.2% increase in the paracentral region, and a 17.2% increase in the peripheral region. Histological cross sections of human corneas also showed a 22.9% increase in peripheral ECD compared with the central region.

CONCLUSIONS

The human cornea has an increased ECD in the paracentral and peripheral regions of cornea compared with the central region. The superior peripheral region of the corneal endothelium has the largest increase in ECD. These data on normal endothelial cell distribution in the human cornea are especially significant as they relate to new surgical techniques and endothelial wound repair.

Assessments of corneal endothelial cell density in growing children and its relationship to horizontal corneal diameter

BACKGROUND

Few studies have been published of corneal endothelial cell density (ECD) in children, especially in relation to the age and corneal size of the individuals. The possible effect of corneal enlargement on the endothelium was studied, and the results were objectively reviewed in relation to literature reports on corneal diameter and age.

METHODS

ECD was assessed in 119 children aged 5 to 15 years after endothelial photography with a noncontact specular microscope (Topcon SP-1000 or SP-2000P), followed by manual digitization of cell overlays. The horizontal corneal diameter, as the visible iris diameter, was measured to 0.5-mm accuracy.

RESULTS

The mean +/- SD value for ECD, calculated using all individual cell area values, was 3542 +/- 510 cells/mm2 (range, 2576 to 5316), whereas it was 3246 +/- 416 cells/mm2 (range, 2404 to 4817) if the mean cell area value from each image was used to calculate ECD. The mean horizontal corneal diameter was 11.48 +/- 0.58 mm (+/- SD). The corneal diameter was not obviously age-related for this group, but there were clear trends for younger children to have higher ECD values than older children (p2, depending on the method for calculating ECD.

CONCLUSIONS

ECD values were found to be significantly correlated to corneal diameter in children aged 5 to 15 years, and this factor should be considered in comparative studies.

Corneal endothelial cell morphology in patients undergoing cataract surgery

PURPOSE

To evaluate the effect of age, gender, axial length, and presence of type II diabetes on corneal endothelial cell morphology in patients undergoing cataract surgery.

METHODS

The corneal endothelial cell morphology was investigated in 1,819 eyes of 1,394 patients before cataract surgery. The parameters examined include cell density, coefficient of variation of cell area, and percentage of hexagonal cells. The effects of age, gender, axial length, and presence of type II diabetes on these parameters were evaluated.

RESULTS

The mean values in endothelial cell density, coefficient of variation of cell area, and percentage of hexagonal cells in all eyes, were 2,543 +/- 254 cells/mm2 (range, 1906-3,252), 0.64 +/- 0.10 (range, 0.34-1.00), and 37.9 +/- 7.1% (range, 17.6-61.7), respectively. Stepwise multiple regression analysis revealed that age was the only explanatory variable to be relevant to corneal endothelial cell density (R = -0.201, p < 0.0001), coefficient of variation of cell area (R = 0.066, p = 0.0046), and percentage of hexagonal cells (R = -0.086, p = 0.0002). The other variables, including gender, axial length, and presence of type II diabetes mellitus, were found to be irrelevant to any of the parameters of corneal endothelial cells.

CONCLUSIONS

Age is the major relevant factor in corneal endothelial cell morphology in patients before cataract surgery.

Corneal disease in patients with chronic renal insufficiency undergoing hemodialysis

PURPOSE

To evaluate alterations of the corneal endothelium in patients undergoing hemodialysis for renal insufficiency.

METHODS

Sixty-six patients undergoing hemodialysis received a complete ophthalmologic examination. The state of the endothelium was assessed using pachymetry and specular microscopy. The group of patients undergoing dialysis was divided according to the time of dialysis, aluminum, product of calcium and phosphate in blood, and parathyroid hormone to analyze the influence of these factors. The possible presence of iron and aluminum in the aqueous humor of patients who underwent and those who did not undergo hemodialysis was also estimated.

RESULTS

Patients undergoing hemodialysis did not have significant corneal edema. Cell density was significantly lower in patients undergoing dialysis than in patients not undergoing dialysis; this reduction appeared to be associated with length of dialysis and was unrelated to serum aluminum and calcium levels. Patients undergoing dialysis did not have cell polymorphism or polymegethism, although there was a tendency toward increased polymegethism with length of dialysis. Aluminum and iron were not increased in the aqueous humor of patients undergoing dialysis.

CONCLUSIONS

The alteration of the endothelium that we found is not related to the elements studied. It is possibly the result of another product dissolved in the anterior chamber or to the alterations of the anterior segment that these patients are known to have.

A histomorphometric study of corneal endothelial cells in normal human fetuses

The purpose of this study was to investigate the histomorphometric change in the normal development of human fetal corneal endothelial cells. Eighty one human fetal corneas, ranging from 12 to 40 weeks of gestation, were examined. For determination of gross parameters, corneal diameter and height were measured. Then the corneal endothelium including Descemet's membrane was stained with hematoxylin-eosin using a flat preparation method. In addition to histologic examination under the light microscope, computer-assisted image analysis was performed to determine the cell area, coefficient of variation in cell area and cell density, in both central and peripheral cornea, from each specimen. Total cell count per cornea was obtained by multiplying endothelial cell density by corneal surface area. Linear and nonlinear regression analysis of gestational age and each parameter were used to model corneal endothelial development during the prenatal period. Fetal cornea grows rapidly throughout the prenatal period. During the same period, mean cell area and total cell count also increases gradually, but there is a steep increase in the total cell count in the early period and of the cell area in the late period. The mean cell density decreases rapidly from 16 015 to 6167 cell x mm(-2). There was no significant difference in all parameters except cell density, between the central and peripheral cornea and the difference in cell density was only 2%. In the early prenatal period, there is a rapid increase of total cell count by mitosis, whereas in the late period enlarged endothelial cells cover the rapidly widening inner corneal surface without a significant change in the total cell count.

Reassessment of the corneal endothelial cell organisation in children

AIM

To assess uniformity of the corneal endothelial cell mosaic in children.

METHODS

36 healthy children (5-11 years old, 16 boys, 20 girls) were assessed by specular microscopy. Endothelial cell density (ECD) was calculated from measured cell areas, and the number of sides/cell noted.

RESULTS

Average values for ECD and cell areas were 3987 cells/mm(2) (95% CI 3806 to 4168 cells/mm(2)) and 278 (SD 85) mm(2) respectively, with normal distribution (COV 28. 2%, range 17.4 to 39.2%) and with the average percentage of six sided cells being 66.6% (8.8%). Cell area was positively correlated to number of cell sides (p <0.01, r(2)=0.993), but the percentage of six sided cells was negatively correlated to ECD (p <0.01, r=0.493).

CONCLUSION

A high ECD occurs in children, but this does not mean there is a high percentage of "hexagons".

The resiliency of the corneal endothelium to refractive and intraocular surgery

PURPOSE

To describe stress factors (phenylephrine and contact lenses) from the corneal epithelium that can affect the corneal endothelium, and to describe the effects of refractive and intraocular surgery on the corneal endothelial structure and function.

METHODS

Significant clinical and experimental publications are reviewed and recent experiments conducted in the author's laboratory to describe the corneal endothelial stresses.

RESULTS

The corneal epithelium serves as a barrier to topical phenylephrine (2.5-10%). In a compromised epithelium, topical phenylephrine will cause drug-induced stromal edema and endothelial vacuolization. Contact lenses are capable of stimulating the epithelial arachidonic acid cascade to release 12(R)hydroxyeicosatetraenoic acid (12(R)HETE) and 8(R)hydroxy-hexadecatrienoic acid (8(R)HHDTrE) to cause endothelial Na+/K+ adenosine triphosphatase (ATPase)-inhibition and polymegethism. Specular microscopy of the corneal endothelial cells after refractive surgery (photorefractive keratectomy [PRK], laser in situ keratomileusis [LASIK], intrastromal rings [INTACs]) has shown that there is minimal effect. However, laser ablation of the stroma within 200 microm of the corneal endothelium will result in endothelial cell structural changes and the formation of the amorphous substance deposited onto Descemet's membrane. Phacoemulsification with a high flow of the irrigation solution can alter the endothelial surface glycoprotein layer. Lidocaine hydrochloride (1%) used as intracameral anesthesia readily diffuses through the corneal endothelium, resulting in stromal uptake and endothelial cell swelling. With phacoemulsification, however, the washout of lidocaine from the cornea (T1/2, 5 minutes) and iris (T1/2, 9 minutes) occurs quickly. Corneal endothelial wound healing after keratoplasty occurs in the following sequence: migration of endothelial cells, development of tight junctions, and the formation of Na+/K+ ATPase pump sites.

CONCLUSIONS

Corneal endothelial resiliency is due to the increased peripheral endothelial cell number for migration, the ability of endothelial cells to form tight junctions to maintain the endothelial barrier, the increase in endothelial Na+/K+ ATPase pump sites under stress, and the ability of the corneal endothelial cells to shift their metabolism of glucose to the hexose monophosphate shunt for the production of nicotinamide adenine dinucleotide phosphate (NADPH) and membrane repair. All of these factors are important, along with the aqueous humor sodium concentration, which establishes the osmotic gradient for corneal deturgescence and transparency.

Assessment of the reliability of human corneal endothelial cell-density estimates using a noncontact specular microscope

PURPOSE

We sought to determine the variance in endothelial cell density (ECD) estimates for human corneal endothelia.

METHODS

Noncontact specular micrographs were obtained from white subjects without any history of contact lens wear, or major eye disease or surgery; subjects were within four age groups (children, young adults, older adults, senior citizens). The endothelial image was scanned, and the areas from > or =75 cells measured from an overlay by planimetry. The cell-area values were used to calculate the ECD repeatedly so that the intra- and intersubject variation in an average ECD estimate could be made by using different numbers of cells (5, 10, 15, etc.).

RESULTS

An average ECD of 3,519 cells/mm2 (range, 2,598-5,312 cells/mm2) was obtained of counts of 75 cells/ endothelium from individuals aged 6-83 years. Average ECD estimates in each age group were 4,124, 3,457, 3,360, and 3,113 cells/mm2, respectively. Analysis of intersubject variance revealed that ECD estimates would be expected to be no better than +/-10% if only 25 cells were measured per endothelium, but approach +/-2% if 75 cells are measured.

CONCLUSION

In assessing the corneal endothelium by noncontact specular microscopy, cell count should be given, and this should be > or =75/ endothelium for an expected variance to be at a level close to that recommended for monitoring age-, stress-, or surgery-related changes.

Cell density of the corneal endothelium in human fetus by flat preparation

PURPOSE

To count the number of the corneal endothelial cells per unit of tissue area in 25 human fetal eyes ranging from 12-40 weeks of gestation with the histologic method.

METHODS

The endothelium including Descemet's membrane was stained with hematoxylin-eosin by the flat preparation method. We photographed the endothelium using light microscopy. The number of nuclei was counted on each photograph. A calibrated micrometer was photographed with the light microscopy, and this was used to measure the number of corneal endothelial cells per square millimeter.

RESULTS

The prenatal endothelial cell density of the human cornea decreases rapidly from 14,095 cells/mm2 (12 weeks of gestation) to 6,820 cells/mm2 (40 weeks of gestation).

CONCLUSION

The estimate of the endothelial cell density at 12 weeks of gestation is twofold higher than the estimate at 40 weeks of gestation.

Intraocular lens implantation in infant monkeys: clinical and histopathological findings

PURPOSE

To determine the long-term effects of intraocular lens (IOL) implantation in infant monkey eyes.

SETTING

Yerkes Regional Primate Research Center, Emory University School of Medicine, Atlanta, Georgia, USA.

METHODS

A 30.00 diopter (D), all-poly(methyl methacrylate) IOL with an overall diameter of 10.0 mm was implanted in the right eye of 11 infant monkeys. Seven monkeys developed postoperative complications and were not followed on a long-term basis. However, 4 monkeys were followed clinically for 4 1/2 years, after which their pseudophakic eyes were examined histopathologically.

RESULTS

The final refractive error in the four pseudophakic eyes with long-term follow-up ranged from -4.75 to +0.75 D. Three of the four eyes had a Soemmering's ring. Only one haptic was in the capsular bag. whereas five had eroded into the iris root/ciliary body. The corneas and posterior segments of the eyes were normal.

CONCLUSION

Two-thirds of the eyes having neonatal IOL implantation experienced significant postoperative complications. Haptic location was suboptimal in all four eyes followed for 4 1/2 years. The diameter of the IOLs implanted in these eyes was probably too large. Some of these complications might have been averted by implanting an IOL with a smaller diameter.

Corneal endothelium and growth factors

Human corneal endothelium is characterized by a low regenerative capacity, mainly because of a low mitotic activity, and therefore complete regeneration of the endothelial layer after injury is precluded. A decrease in endothelial cell density and an abnormal cell mosaic, which may occur after many conditions, can compromise the integrity of the endothelial monolayer, resulting in corneal decompensation with reduced vision and eventual need for penetrating keratoplasty. It would be beneficial to have growth factors that can help to maintain or restore the integrity of this delicate endothelial monolayer by maintaining or increasing the endothelial cell density or to stimulate the regeneration during wound healing. Growth factors represent a group of signalling peptides which influence diverse cellular processes, including cell proliferation, differentiation, migration and survival. One of the areas that has received great interest is its enhancement of wound healing. In this review the effects of three most effective growth factors (EGF, PDGF, FGF) on corneal endothelium, especially on wound healing in human corneal buttons, will be discussed.

Topical chemotherapy for conjunctival melanoma

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