A rare case of oguchi disease exhibiting the classic Mizuo-Nakamura phenomenon

Abstract

Oguchi disease also called congenital stationary night blindness is an autosomal recessive genetic condition first identified in Japan with a few cases reported in other countries like Europe, America, India and Pakistan. We report one such case exhibiting the Mizuo-Nakamura phenomenon with a reduced amplitude on the b-wave of the rod electroretinogram advocating this diagnosis. A 40-year-old man presented with complaints of non-progressive decrease in vision as the day progressed for 6 months with normal vision during the day in both eyes. There was no history of trauma or any other ocular or systemic disease. His parents had a second-degree consanguineous marriage and his father experienced similar symptoms. Visual acuity for distance was 6/6 and N6 for near in both eyes. His anterior segment and posterior segments were normal. When the patient was put to dark adaptation for 3 hours, there was a change in his fundus background colour from grey to red (Mizuo-Nakamura phenomenon). The b-wave amplitude was decreased on the rod electroretinogram. The cone electroretinogram on the other hand was normal. All this was confirmed by his genetic study which favoured this diagnosis.This disease presents with features similar to retinitis pigmentosa in terms of mutations in the SAG gene This highlights the importance of the Mizou-Nakamura phenomenon in formulating a confirmatory diagnosis and treatment protocol.