Toxic/nutritional optic neuropathy

A 30-year-old Indian man reported difficulty using a camera with his left eye for several years. He denied any toxic exposure (e.g., poisons, heavy metals, or chemicals). He was not a vegan and reported eating three meals per day. He denied any vomiting, anorexia, or bariatric surgery. There was no history of tuberculosis (TB) or treatment with anti-TB medications (e.g., isoniazid or ethambutol). He denied any other neurological symptoms except for mild photophobia. The remainder of his medical, surgical, and social history was unremarkable. On examination, his best-corrected visual acuity was 20/20−2 in the right eye (OD) and 20/60−2 in the left eye (OS). Pupils were 4 mm in the dark and 2 mm in the light and there was a left relative afferent pupillary defect (RAPD). He correctly identified 8/8 Ishihara color plates OD but only 1.5/8 OS. The extraocular movements, intraocular pressures, and slit lamp examinations were normal bilaterally (OU). Dilated funduscopic examination demonstrated mild temporal pallor OU (Fig. 3.1). Automated visual fields (Humphrey 24-2) demonstrated a mild bilateral central scotomas OS > OD (Fig. 3.2). Magnetic resonance imaging (MRI) of the brain and orbits with and without gadolinium and fat suppression were normal and demonstrated no optic nerve enhancement or compressive lesion. Optical coherence tomography (OCT) showed papillomacular bundle nerve fiber layer dropout OU.