Folic acid has a fundamental role in central nervous system (CNS) function at all ages, especially the methionine synthase-mediated conversion of homocysteine to methionine, which is essential for nucleotide synthesis and genomic and non-genomic methylation. Folic acid and vitamin B12 may have roles in the prevention of disorders of CNS development, mood disorders, and dementias, including Alzheimer disease and vascular dementia in elderly people. The authors examined the peripapillary retinal nerve fibre layer thickness (RNFLT) in patients with nutritional folic acid deficiency using optical coherence tomography (OCT). Patients were divided into two groups according to blood folic acid levels: blood folic acid < 7 nmol/L as Group 1 and < 7 nmol/L as Group 2. Peripapillary RNFL measurements were performed. There were significant positive correlations between serum folate levels and RNFLT in all quadrants (p < 0.05), except for the temportal quadrant (p = 0.41).