Journal of Clinical Ophthalmology and Research

ORIGINAL ARTICLE
Year
: 2020  |  Volume : 8  |  Issue : 3  |  Page : 95--99

Study of corneal endothelial morphology in primary open angle glaucoma and pseudo-exfoliatiive glaucoma patients compared with age related normal


Pooja Bhomaj1, Shilpa Umarani2, Janavi Kudache2,  
1 Department of Ophthalmology, Lions NAB Eye Hospital, Miraj, Maharashtra, India
2 Department of Glaucoma, Lions NABH Eye Hospital, Miraj, Maharashtra, India

Correspondence Address:
Pooja Bhomaj
Shanti Saroj Netralaya, 901/902, Beside Sundar Nagar, A. N. Gaikwad Road, Miraj - 416 410, Maharashtra
India

Abstract

Objectives: The corneal endothelium does not regenerate, and hence, its integrity is essential to maintain corneal clarity. In view of scarce and contradicting literature on the influence of open-angle glaucoma on endothelial cell density (ECD), and lack of direct head-to-head studies comparing the ECD in eyes with primary open-angle glaucoma (POAG) and pseudoexfoliation glaucoma (PXFG), we conducted a cross-sectional study to compare the ECD in these eyes in comparison with normal eyes without glaucoma. Materials and Methods: This was a cross-sectional study carried out at a tertiary eye care center in Western India. We enrolled 141 eyes of 141 participants in the study with 47 eyes each in the controls: POAG and PXFG groups. Group differences across the three groups in the continuous variables were analyzed using the analysis of variance or the Kruskal–Wallis test. Differences across the POAG and PXF groups were assessed using the Student t-test of the Wilcoxon rank-sum test for nonparametric variables. Group differences across categorical variables were analyzed using the Chi-square or Fischer’s exact test. Results: In multivariable linear regression analysis adjusted for age, eyes with POAG had an endothelial cell count of 185 cells/mm2 lower than normal eyes (95% confidence interval [CI] =132–238 cells lower, P < 0.001). Similarly, eyes with PXFG had an endothelial cell count of 215 cells lower than normal eyes (95% CI = 162–267 cells lower, P < 0.001). Conclusions: Eyes with POAG and PXFG have lower endothelial cell count compared to age-matched controls.



How to cite this article:
Bhomaj P, Umarani S, Kudache J. Study of corneal endothelial morphology in primary open angle glaucoma and pseudo-exfoliatiive glaucoma patients compared with age related normal.J Clin Ophthalmol Res 2020;8:95-99


How to cite this URL:
Bhomaj P, Umarani S, Kudache J. Study of corneal endothelial morphology in primary open angle glaucoma and pseudo-exfoliatiive glaucoma patients compared with age related normal. J Clin Ophthalmol Res [serial online] 2020 [cited 2021 Apr 17 ];8:95-99
Available from: https://www.jcor.in/text.asp?2020/8/3/95/302197


Full Text



The corneal endothelium is a vital structure that does not regenerate and hence its integrity is essential to maintain corneal clarity. The endothelial cell density (ECD) gradually diminishes with age, and there is good evidence to show that cell loss is accelerated following anterior segment surgeries such as phacoemulsification and trabeculectomy. Corneal endothelial cell loss has been shown to occur in different forms of glaucoma. Primary angle-closure glaucoma is known to be associated with accelerated endothelial cell loss,[1] especially after acute attacks[2] and following peripheral iridotomy.[3] However, the relationship between ECD and various forms of open-angle glaucoma is less well studied. Some authors have shown no influence of open-angle glaucoma on the ECD,[4] others have shown lower ECD in eyes with primary open-angle glaucoma (POAG) but not with normal-tension glaucoma (NTG),[5] while other report lower cell counts in NTG compared to POAG.[6] Finally, some authors show a blanket reduction in ECD in all eyes with glaucoma and suggest that the magnitude of reduction in ECD depends on the type of glaucoma.[7],[8] The proposed mechanisms for lower ECD in eyes with glaucoma include direct damage from persistently elevated intraocular pressure (IOP), glaucoma medication toxicity, and hypoxic damage to endothelial cells due to altered aqueous drainage or a combination of these.[8],[9] Pseudoexfoliation is known to be associated with a form of open-angle glaucoma that is more severe in nature with higher IOP levels and hence is more difficult to control with topical antiglaucoma medications. Pseudoexfoliation glaucoma (PXFG) is known to be associated with lower ECD than those with normal IOP of the same age.[10],[11],[12] The exfoliation material is seen to be deposited over the corneal endothelium which is postulated to cause direct endothelial cell toxicity and cell loss.[11],[12]

In view of scarce and contradicting literature on the influence of open-angle glaucoma on ECD, and lack of direct head-to-head studies comparing the ECD in eyes with POAG and PXFG, we conducted a cross-sectional study to compare the ECD in these eyes in comparison with normal eyes without glaucoma and find factors predictive of the ECD in these eyes.

 Materials and Methods



This was a cross-sectional study carried out at a tertiary eye care center in Western India between April 2016 and May 2017. The study was approved by the institutional ethics committee and was performed in accordance with the Tenets of the Declaration of Helsinki. Informed consent was obtained from all the participants before enrollment. Consecutive patients who were more than 18 years of age and diagnosed with either POAG or PXFG for a minimum duration of 6 months and willing to provide informed consent were invited to participate in the study. Patients without glaucoma who were visiting the outpatient department for other reasons were enrolled as controls. Exclusion criteria included those with any form of angle closure, other diseases associated with secondary glaucomas such as uveitis, trauma, etc., preexisting corneal disease, coexistent retinal diseases affecting vision, and those who had previous ocular surgeries including cataract surgery. For controls, any diagnosis other than refractive error and age-related cataract were excluded from the study. At time of enrollment, patients’ demographics, duration of glaucoma, and history of systemic illness including diabetes and hypertension were recorded. The type and frequency of antiglaucoma medications were recorded for those with glaucoma. The best-corrected visual acuity (BCVA) was tested by a trained optometrist followed by a comprehensive dilated ophthalmic examination. Slit-lamp findings such as the presence of corneal lesions and documentation of PXF material were noted. Those with nuclear sclerosis or nuclear opalescence Grade 2 or worse, presence of posterior subcapsular cataract or cortical cataract more than 4 clock hours were considered to have significant cataract. Gonioscopy was performed using the four-mirror standard gonioscopy under dim illumination and findings for angle configuration and presence of PXF material in the angle structures were recorded. IOP was measured during the study visit using the Goldmann applanation tonometry. Dilated fundus examination was carried out to document the cup-to-disc (CD) ratio, neuroretinal rim, and retinal nerve fiber layer loss. Endothelial cell parameters including the cell density (ECD), coefficient of variation (CV), and proportion of hexagonal cells was measured using the Topcon SP-3000P noncontact specular microscope (Topcon, Japan). Endothelial cells were counted using manual variable-frame technique and by automated counting of cells by the software of the specular microscope. In this method, the area of interest was marked, and the software counted the cells and gave the parameters automatically. The counts were repeated three times by a grader masked to the glaucoma status of the patient, and a mean of the three counts was used for statistical analysis. On the day of enrolment, prior to dilatation, all patients with glaucoma also underwent automated visual field testing with the Humphrey visual field analyzer (HFA 3) using the SITA 30-2 standard protocol. The mean deviation (MD) and pattern standard deviation were recorded following a reliable visual field test. Central corneal thickness was also measured using ultrasound method. The main outcome measure was difference in ECD, CV, and proportion of hexagonality of corneal endothelial cells between eyes with POAG, PXFG, and normal eyes.

The sample size was calculated based a pilot study of 15 eyes in each group, which showed a 20% lower ECD count in eyes with POAG compared to controls. Assuming 1:1:1 distribution of patients in the three groups, 90% power (a Z.05), and a precision error of 5% to detect a difference of 20% or more in ECD between the three groups, the required sample size was calculated to be 47 in each group. In patients with bilateral disease, the eye with more severe glaucoma based on MD was chosen for statistical analysis. All continuous variables were expressed as mean with standard deviation or median with interquartile range (IQR) and categorical variables were expressed as proportions (n, %). The BCVA was converted into logarithm of minimal angle of resolution (logMAR) for statistical analysis. Group differences across the three groups in the continuous variables were analyzed using the analysis of variance or the Kruskal–Wallis test. Differences across the POAG and PXF groups were assessed using the Student t-test of the Wilcoxon rank-sum test for nonparametric variables. Group differences across categorical variables were analyzed using the Chi-square or Fischer’s exact test. Factors predicting the endothelial cell count were analyzed using univariate and multivariable linear regression analysis and results were expressed as beta-coefficients with 95% confidence intervals (CI). Covariates were selected from those with P < 0.1 at the univariate stage, and those who were felt to be clinically relevant to the outcome. The best-fit model was arrived at using step-wise forward and backward regression. Regression diagnostics were run to find the influence of outliers and other leverage points. All data were entered into Microsoft and imported into STATA 12.1 i/c statistical software package (STATA Corp, Fort Worth, Texas, USA) for statistical analysis. P <0.05 was considered statistically significant.

 Results



We enrolled 141 eyes of 141 participants in the study with 47 eyes each in the controls, POAG and PXFG groups. The mean age of the participants was 60.4 + 5.6 years (median = 60 years, IQR = 52–70 years, range = 50–70 years) and 69% were men. There was an equal distribution of the right (n = 72, 51%) and left eyes (n = 69, 49%). The mean BCVA was 0.17 + 0.13 logMAR (median = 0.2 logMAR, IQR = 0–0.2 logMAR, range = 0–0.5 logMAR) and the mean spherical equivalent was −1.37 + 2.8 D. The mean duration of glaucoma in POAG and PXFG eyes was 11.2 + 4.4 months (median = 12 months, IQR = 8–14 months, range = 6–24 months). Timolol monotherapy was the most common antiglaucoma treatment being used by patients (n = 30, 32%), followed by latanoprost (n = 14, 15%) and combination of latanoprost and timolol (n = 14, 15%). A few patients were using brimonidine either alone (n = 12, 13%) or in combination with timolol (n = 8, 8.5%). Minority patients were using a combination of dorzolamide with timolol (n = 9, 10%). There were no significant differences in type of drug being used by patients with POAG and PXFG. A comparison of the demographics and clinical parameters across the three groups is shown in [Table 1]. Patients with POAG had more diabetes compared to the rest. The mean IOP and CD ratio were significantly higher in the POAG and PXFG groups compared to normal eyes. PXFG had significantly higher IOP compared to the POAG group [Table 1]. Furthermore, the PXFG group had slightly better BCVA, lower duration of glaucoma, and lower CD ratio compared to eyes with POAG. Normal eyes had significantly higher endothelial cell counts compared to POAG and PXFG eyes [Figure 1]. The endothelial cell count reduced with age in all three groups [Figure 2]. Normal eyes also had better parameters related to the quality of the endothelial cell layer such as lower CV and higher proportion of hexagonal cells [Table 1]. On univariate analysis, advancing age, higher IOP, longer duration of glaucoma, and having POAG and PXFG were associated with lower endothelial cell count [Table 2]. On step-wise variable selection, age was the only covariate used to adjust the endothelial cell count. In multivariable linear regression analysis adjusted for age, eyes with POAG had an endothelial cell count of 185 cells/mm2 lower than normal eyes (95% CI = 132–238 cells lower, P < 0.001). Similarly, eyes with PXFG had an endothelial cell count of 215 cells lower than normal eyes (95% CI = 162–267 cells lower, P < 0.001). In age-adjusted models, compared to POAG, eyes with PXFG had 29 cells/mm2 lower (95% CI = −79–21 cells), although this was not statistically significant (P = 0.25). After adjusting for age, eyes with POAG (b-coefficient = 4.29, 95% CI = 3.2–5.4, P < 0.001) and PXFG (b-coefficient = 4.38, 95% CI = 2.5-12.8, P < 0.001) had significantly higher CV values. Similarly, POAG (b-coefficient = −6.5, 95% CI = −7.9 to −5.1, P < 0.001) and PXFG eyes (b coefficient = −7.3, 95% CI = −8.7 to −5.8, P < 0.001) had significantly lower proportion of hexagonal cells compared to normal eyes after age adjustment.{Table 1}{Figure 1}{Figure 2}{Table 2}

 Discussion



We found that eyes with POAG and PXFG have significantly lower ECD, with almost 200 fewer endothelial cells/mm3 compared to normal eyes of the same age. Eyes with PXFG had the lowest ECD, though their difference from POAG was not statistically significant. Age was the other important influencing factor of ECD with older patients having significantly lower cell counts. In addition, normal eyes had endothelial cells with more uniform morphology, as evidenced by the lower CV and higher proportion of hexagonality compared to eyes with glaucoma. In a recent study, de Juan-Marcos et al. compared the ECD and morphology of a total of 166 eyes with PXF (n = 36), PXFG (n = 30), POAG (n = 40), and normal eyes (n = 60) and reported the mean ECD of 2565 cells/sq.mm in normal group, whereas PXFG group had ECD of 2246 cells/sqmm and POAG had ECD of 2294 cells/sq.mm. Similarly, the CV in the normal group was 33, in PXFG and POAG eyes, it was 36. We report similar trends from our series, though glaucomatous eyes had almost 100 cells fewer in our series. This study and our results show that not only is there lower endothelial cell count but also there is considerable pleomorphism and polymegathism in eyes with POAG and PXFG, though there appears to be no real difference with respect to type of glaucoma. Previous study report contradicts findings of ECD in POAG compared to normal eyes. Whereas Korey et al.[4] and Lee et al.[6] show no reduction in ECD in POAG eyes, others such as Zarnowski et al.[7] and Gagnon et al.[8] show lower ECD. In a literature review, Palko et al. found that eyes with pseudoexfoliation had a slightly lower ECD compared to controls in most studies, though the trend of lower ECD was significantly greater in eyes with PXFG than in eyes with PXF without glaucoma.[11] Many other authors have shown lower ECD in eyes with PXFG compared to normal eyes, though this relationship is not as clear in eyes with POAG. Endothelial cells are hexagonal in shape and are arranged in a mosaic pattern such that they maintain a physical barrier and prevent aqueous from entering the corneal stroma. They also have a pump mechanism which allows the stroma to remain anhydrous. In view of these functions, not only the ECD but also the morphology is essential in maintaining corneal clarity. We found that both of these, i.e., density and morphology of the corneal endothelium is affected in eyes with POAG and PXFG. The mechanisms of damage in these two distinct diseases may be relatively different. Raised IOP is thought to contribute to endothelial damage due to a compression effect; however, in in vitro imitation models, Mortensen and Sperling did not find reduction in ECD in cadaveric eyes subjected to a pressure gradient for 24 h. We postulate that it may be the stagnation of aqueous circulation with resultant reduction in availability of vital metabolites to the endothelial cells that result in loss of cell number and architecture, rather than mere raised IOP. In PXFG, precipitation of the PXF material on the endothelial surface is thought to be due to production of PXF by the endothelial cells themselves, thereby indicating that the cells have altered metabolic activity and are prone for damage irrespective of raised IOP.[13] The increased pressure due to trabecular outflow obstruction probably adds to the stress on the endothelial cells, and hence, the ECD is found to be consistently lower in eyes with PXFG compared to eyes with PXF without glaucoma.[11],[12] We also performed a head-to-head comparison of endothelial parameters in eyes with POAG and PXFG and did not find significant differences, though PXFG had 29 cells/sq.mm fewer than POAG in age-matched models. We excluded pseudophakic eyes to eliminate the confounding effect this may have had on the ECD. The drawback of our study is the lack of longitudinal data to show rate of progressive loss of ECD, especially comparing POAG to PXFG. The merits are the relatively good sample size and performing endothelial counts multiple times by a masked observer to prevent measurement errors and bias. In addition, we also report on morphological parameters such as CV and hexagonality which clearly indicate pleomorphism and polymegathism in these eyes.

 Conclusion



In conclusion, eyes with POAG and PXFG have lower endothelial cell count and have altered morphology compared to age-matched controls. Every attempt should be made to protect these cells from further damage during subsequent anterior segment procedures such as phacoemulsification. Future studies should report on changes in ECD over time in glaucomatous eyes and identify factors predictive of accelerated endothelial loss.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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