Differences in the thickness of various layers of the macular in patients with and without serum vitamin D deficiency in type 2 diabetes mellitus patients without diabetic retinopathy

To investigate the impact of vitamin D deficiency (VDD) on retinal and choroidal thickness (CT) in patients with diabetes mellitus (DM) without diabetic retinopathy (DR) using swept-source optical coherence tomography (SS-OCT). Fifty-six eyes from 56 DM-NDR patients were included and divided into two groups based on serum 25(OH)D levels: VDD Group (25(OH)D ≤ 20 ng/mL, n=27) and non-VDD Group (25(OH)D > 20 ng/mL, n=29). Macular OCT imaging (6 × 6 mm) was performed and divided into the foveal region (0-1 mm), parafoveal region (1-3 mm), and perifoveal region (3-6 mm). The latter two zones were further subdivided into four quadrants: temporal, superior, nasal, and inferior (T, S, N, I). Retinal layer (RL), retinal nerve fiber layer (RNFL), ganglion cell layer plus inner plexiform layer (GCL-IPL), and CT were measured. Serum vitamin D levels were quantified using electrochemiluminescence immunoassay (ECLIA). Significant differences in RL and GCL-IPL thicknesses were observed within the foveal region, and in RNFL thickness across all quadrants in the parafoveal region (p<0.05). RL thickness showed significant differences in the superior and temporal quadrants (p<0.05). GCL-IPL thickness showed significant differences in all quadrants except the inferior quadrant (p<0.05). VDD is associated with reduced RL, RNFL and GCL-IPL thicknesses, particularly in the parafoveal region, indicating that these layers may serve as sensitive biomarkers for VDD-induced neurodegeneration in diabetic patients. Vitamin D deficiency may be a risk factor for the progression of DR.