Retinal Nerve Fibre Layer and Ganglion Cell Complex Thickness in Diabetes Mellitus without Diabetic Retinopathy

Abstract

Introduction: Diabetic retinopathy is on the rise and understanding mechanisms of retinal neurodegeneration in diabetes mellitus will help in halting retinopathy.

Objective: The study was done to assess the retinal nerve fibre layer and ganglion cell complex thickness in type two diabetes mellitus without clinically evident vascular retinopathy and compare them with the normal population to understand the early neurodegenerative changes.

Methodology: This was a hospital-based, prospective, observational study conducted in South India from 2022 May to 2023 March. This study included one hundred and seventeen eyes with type two diabetes mellitus without clinical diabetic retinopathy and 115 normal age-matched controls after ethical approval using a consecutive sampling technique. Participants with other systemic co-morbidities and retinal pathology were excluded. Average, superior, and inferior retinal nerve fibre layer thickness and average, superior, inferior, inferonasal, superonasal, superotemporal, and inferotemporal macular ganglion cell complex thickness were measured using spectral-domain optical coherence tomography. A student's unpaired t-test was used for comparing the thickness between cases and controls, and analysed using SPSS Statistics version 26.

Result: The retinal nerve fibre layer thickness was significantly reduced in all quadrants in type two diabetes mellitus without diabetic retinopathy when compared to normal controls (p <0.001), with the mean nerve fibre layer thickness of 100.3μm ± 12.5μm in cases and 110.9μm ± 8.7μm in controls. The mean macular ganglion cell complex thickness was also significantly decreased in diabetes without retinopathy (p <0.001), with values of 99.9μm ± 8.1μm in diabetics and 109.3μm ± 4.9μm in controls. In diabetics, increased glycosylated haemoglobin correlated negatively with the nerve fibre layer and ganglion cell complex thickness.

Conclusion: Neurodegeneration of the retinal nerve fibre layer and ganglion cell complex in diabetics occurs before clinically visible vascular changes appear. Higher glycosylated haemoglobin is a risk factor for early neurodegeneration.