Impact of Prolonged and Unsupplemented Vegan Diet on Retinal Structure and Visual Function

Vitamin B12-deficiency nutritional optic neuropathy (NON) is a potentially preventable cause of permanent visual loss that may occur in individuals following prolonged unsupplemented vegan diets. This cross-sectional observational study assessed peripapillary retinal nerve fiber layer (pRNFL) and ganglion cell complex (GCC) thickness using optical coherence tomography (OCT) in vegan patients with permanent visual loss secondary to vitamin B12-deficiency NON and compared the findings with those of age-matched healthy controls. All participants underwent OCT and standard automated perimetry, and clinical data, dietary history, duration of diet and symptoms, serum vitamin B12 levels, best-corrected visual acuity, mean deviation values, and pRNFL and GCC measurements were evaluated. A total of 22 eyes from 11 vegan patients and 22 eyes from 11 healthy controls were included. Vegan patients showed significant temporal pRNFL thinning and diffuse GCC thinning compared with controls. Significant correlations were observed between the duration of the vegan diet and symptoms, the severity of visual field loss, and several OCT parameters, particularly GCC thickness. Patients with permanent visual loss due to vitamin B12-deficiency nutritional optic neuropathy associated with prolonged unsupplemented vegan diets demonstrated marked temporal pRNFL thinning and diffuse macular GCC loss on OCT, with GCC measurements correlating with symptom duration. These findings support the usefulness of OCT for documenting structural damage in established nutritional optic neuropathy. However, larger longitudinal studies including asymptomatic or early symptomatic vegan individuals are needed to determine whether OCT can detect early neuroaxonal loss or predict visual outcomes.