Ganglion cell layer thinning in diabetic patients without retinopathy: related or unrelated to total macular thickness?

Purpose: Reduction of ganglion cell layer thickness may occur in diabetic patients without retinopathy. The relationships of this preclinical finding with retinal thickness or reduced parafoveal vessel density have not been established. This study investigated the relationships of ganglion cell layer thickness with retinal thickness and parafoveal vessel density in patients with and without diabetes. Methods: This was an observational, cross-sectional, prospective study that used optical coherence tomography angiography to compare non-diabetic patients (group 1) with diabetic patients without retinopathy (group 2). Ganglion cell layer thickness, macular thickness, and parafoveal vessel density (central, inner, and complete) medians were compared between groups (Mann-Whitney U test), and their relationships were assessed in each group (Spearman Rho test). Results: In total, 68 eyes were included in this study: 34 in group 1 and 34 in group 2. Ganglion cell layer thickness did not differ between groups in any sector. There were strong positive correlations between fields 2 (superior parafoveal), 3 (temporal parafoveal), and 4 (inferior parafoveal) of the optical coherence tomography macular thickness map and the ganglion cell layer thickness in all sectors in both groups. Central vessel density mean was lower in diabetic patients. In group 1 alone, thickness changes in the inferior and nasal inferior ganglion cell layer sectors were partially explained by inner vessel density (r²=0.32 and r²=0.27). Conclusions: Mean ganglion cell layer thickness was not lower in diabetic patients without retinopathy than in non-diabetic patients. Moreover, it exhibited a substantial correlation with total macular thickness. Parafoveal vessel density decreased before ganglion cell layer thinning was observed.