Association Among Serum Vitamin D Levels, Visual Field Alterations, and Optical Coherence Tomography Parameters: A Clinical Correlation Study

Vitamin D deficiency is increasingly recognized as a systemic factor influencing retinal health through inflammatory, neuroprotective, and vasculotropic pathways. Evidence regarding early retinal alterations in otherwise healthy adults remains limited. This cross-sectional study evaluated 120 eyes from 60 healthy adults stratified by serum 25(OH)D levels into <30 ng/mL (n = 60) and ≥30 ng/mL (n = 60). All subjects underwent optical coherence tomography (OCT), OCT angiography (OCTA), visual field testing, and contrast sensitivity assessment. Central macular thickness (CMT), ganglion cell complex (GCC) thickness, and perfusion density in the superficial and deep capillary plexuses (SCP, DCP) were compared between groups. Vitamin-D-insufficient eyes showed significantly reduced CMT (267.66 ± 13.31 µm vs. 274.69 ± 14.96 µm; <i>p</i> = 0.035). GCC thinning was significant only in the inner inferior nasal sector (70.7 ± 13.14 µm vs. 76.45 ± 12.12 µm; <i>p</i> = 0.030), whereas other GCC sectors were comparable between groups. Perfusion density was lower in the DCP across whole, inner, and outer regions (all <i>p</i> < 0.001) and in the SCP inner (<i>p</i> = 0.027) and outer (<i>p</i> = 0.009) regions, while whole SCP did not differ (<i>p</i> = 0.065). FAZ area was numerically larger in vitamin-D-insufficient eyes but was not statistically different (<i>p</i> = 0.168). Functionally, retinal sensitivity decline was greater in vitamin-D-insufficient eyes (-2.89 ± 1.29 dB vs. -2.16 ± 1.04 dB; <i>p</i> = 0.003), and mean central sensitivity was lower (<i>p</i> = 0.010), whereas contrast sensitivity did not differ between groups. Serum vitamin D levels < 30 ng/mL are associated with early, subclinical, structural and microvascular retinal alterations in healthy adults, supporting a potential role of hypovitaminosis D as a modifier of retinal integrity.