Retinal neurodegeneration in diabetic patients without diabetic retinopathy

Background: Spectral-domain optical coherence tomography (SD-OCT) is a non-invasive technology that has become an essential instrument for precise assessments of retinal thickness with high resolution and increased definition of the various retinal layers. Our objective was to assess the retinal neurodegeneration in cases with type 2 diabetes mellitus (T2DM) without diabetic retinopathy (DR) using OCT.Methods: This prospective cohort trial was performed on two groups: 25 eyes of diabetic patients with no signs of DR, 25 eyes of non-diabetic individuals with normal retina as a control group. We included cases with T2DM who doesn’t show signs of DR, eyes with clear ocular media, best corrected visual acuity (BCVA) of 0.4 or more for both groups. BCVA, intraocular pressure, fundus examination measurements and OCT were performed on the cases.Results: Macular thickness was significantly decreased in diabetic group compared to non-diabetic group in all sectors except central 1mm zone. Ganglion cell layer thickness was significantly decreased in diabetic group compared to non-diabetic group in all sectors as regards: superotemporal, superonasal, superior, average, inferotemporal, inferonasal and inferior sectors. RNFL thickness was significantly decreased in diabetic group compared to non-diabetic group as regards: average, nasal and temporal quadrants. A significant negative correlation was reported between duration of DM and ganglion cell layer thickness and RNFL in all sectors. A significant negative correlation was reported between HbA1c and ganglion cell layer thickness as regards (average, superior, superonasal, and superotemporal sectors), furthermore, a significant negative correlation was found between HbA1c and RNFL thickness in (average, superior quadrant).Conclusions: Retinal neurodegeneration including macular GCL, peripapillary RNFL and macular thinning are early events in DR before vascular events.