Changes of Retinal Nerve Fiber Layer Thickness in Patients with Type 2 Diabetes

Background: Deterioration of quality of vision starts early in diabetes, before clinical retinopathy becomes evident. This probably indicates the early signs of neuronal dysfunction. Retinal nerve fiber layer (RNFL) is an important structural neuron in the retinal layer which is often affected in the early pathological stages of diabetic retinopathy. Aim of Study: To assess the changes in retinal nerve fiber layer (RNFL) thickness associated with type 2 diabetes mellitus (DM) with or without diabetic retinopathy (DR) and to correlate these changes with the stage of retinopathy. Patients and Methods: This observational study included 39 patients with type 2 DM in three groups as per the stage of DR. Group 1 included eyes without DR. Group 2 included eyes with mild non-proliferative diabetic retinopathy (NPDR). Group 3 included eyes with moderate NPDR. Severe NPDR, PDR, and/or macular edema were excluded. All participants underwent full ophthalmological assessment followed by imaging via Cirrus HD-OCT 5000 optical coherence tomography (Carl Zeiss Meditec, Jena, Germany). For each participant, macular and optic disc scans were obtained. Blood samples were with drawn for serum creatinine and glycosylated haemoglobin (Hb A1c). Results: Thirty-nine eyes of type 2 diabetic patients were enrolled in this study; twelve eyes in group 1, 14 in group 2, and 13 in group 3. We found highly significant differences ( p <0.001) between the groups regarding the duration of diabetes and levels of HbA1c. Decremental thinning in the measurements of the average, superior, inferior, and temporal RNFL thickness were observed with the progression of DR. In groups 2 and 3 negative moderate correlations ( r =0.55 and 0.6 respectively) were found between the duration of DM and the average thickness of the RNFL. Conclusion: With the advancement in DR, we observed a reduction of RNFL thickness. More research is needed to study the effect of RNFL reduction on the progress of retin- opathy.