Corneal Endothelial Morphology and Central Corneal Thickness Changes in Type 2 Diabetes Mellitus using Specular Microscopy and Ultrasonic Pachymetry: A Cross-sectional Comparative Study

Abstract

Introduction: Diabetes Mellitus (DM) is a metabolic condition characterised by chronic hyperglycaemia, causing raised blood glucose levels which result in microvascular and macrovascular disorders and may introduce ocular manifestations including changes in corneal Endothelial Cell Density (ECD), corneal thickness, and intraocular pressure. It is clinically important to analyse the corneal endothelial status in patients with type II DM as preoperative corneal endothelial cell dysfunction may cause more corneal endothelial cell damage postoperatively leading to corneal decompensation. With the advent of precise and better measurement tool Central Corneal Thickness (CCT) and corneal endothelial morphology measurement has become more accurate. Aim: To compare corneal endothelium cell density, polymorphism, polymegathism and CCT in type 2 DM with age-matched, non diabetic control subjects using CEM-530 Specular microscope and ultrasonic pachymeter Tomey SP-100. Materials and Methods: This cross-sectional, comparative study was conducted at Eye Department at ESI Post Graduate Institute of Medical Sciences and Research, Basaidarapur, Delhi, India, from October 2018 to November 2019. Patients with ages between 40 to 70 years of either gender who were diagnosed to have DM were recruited in the study through non probability convenience sampling. A total of 150 subjects that met the inclusion criteria and exclusion criteria were included in the study. Seventy five known type 2 DM patients were enrolled in diabetic group (case group) and 75 non diabetic, age-matched subjects were enrolled as control group. Cases were classified under three major groups, namely on the basis of duration of DM and severity of Diabetic Retinopathy (DR) and glycaemic control {glycosylated haemoglobin (HbA1c) level}. All the findings were endorsed on a predesigned performa. Statistical Package for Social Sciences (SPSS) version 17.0 was used for analysis of data. Age and corneal parameters compared using unpaired t-test in diabetic and control group. Also, for comparison in between subgroup of diabetic patients on HbA1c level done by using Analysis of Variance (ANOVA) test. Chi-square test applied for categorical variables. Results: Among the 150 patients evaluated, type 2 DM patient’s corneas (540.51±32.578 µ) were thicker as compared to control group 517.51±22.155 µ (p-value<0.001). The mean ECD of control and diabetic group patients was 2723.75±287.253 cells/mm2 and 2716.11±296.081 cells/mm2 , respectively, found insignificant (p-value=0.821). The mean Coefficient of Variation (CV) of cell area of control and diabetic patients was 28.87±3.950 and 29.85±4.027, respectively, and was significant (p-value=0.034). The mean percentage of endothelial Hexagonal cells (HEX%) of control and diabetic patients were 67.39±6.419 and 67.41±5.493, respectively and was non significant (p-value=0.985). Thus, statistically significant difference was found with CCT (p-value<0.001) and CV (p-value=0.034) but not with ECD and hexagonality, between control and diabetic eyes. There was a correlation between CCT, CV, HEX% and ECD with duration of DM2 but it was statistically insignificant. There were higher CCT, CV and HEX% and lower ECD in >10 years of duration of diabetes mellitus than in patients with duration of diabetes mellitus ≤10 years. There was a correlation of CCT, CV, ECD and HEX with HbA1c level. There were significant higher CCT and CV values in >7% HbA1c level group than in group with ≤7% HbA1c level. There was also increased ECD in >7% group, but it was found to be insignificant. Percentage of hexagonality in >7% HbA1c level group was lower than in group with ≤7% HbA1c level, but found insignificant. There were higher values of CCT and CV in Non Proliferative Diabetic Retinopathy (NPDR) subgroup compared to Proliferative Diabetic Retinopathy (PDR) and no Diabetic Retinopathy group. CCT values were significant (p-value=0.007), so as CV values (p-value=0.001). There was increase in HEX% (p-value=0.005) which was significant, along with lower ECD in NPDR (p-value=0.143), group which was insignificant. Conclusion: The present study documented that DM has considerable effects on all the layers of the cornea especially endothelial layer, causes reduction of ECD and increased CV. Diabetic cornea has increased CCT and lower percentage of hexagonal cells than normal subjects. In addition, there is a correlation between the changes in corneal parameters like ECD, CV, HEX%, CCT with the duration of DM and severity of DR and glycaemic control {glycosylated haemoglobin (HbA1c) level}.