Oguchi disease

Diagnosis

Patients present with nonprogressive night blindness from young childhood or birth, while day vision remains normal. They often report improved light sensitivity after remaining in a darkened environment. Visual fields are normal, but the fundi show a diffuse or patchy silver-gray or golden-yellow metallic sheen, with retinal vessels standing out in relief. Prolonged dark adaptation of three hours or more causes this discoloration to disappear, revealing a normal reddish appearance—the Mizuo-Nakamura phenomenon, attributed to overstimulation of rod cells.

Conditions with similar fundi include cone dystrophy, X-linked retinitis pigmentosa, and juvenile macular dystrophy, but these lack the Mizuo-Nakamura phenomenon. Electroretinographic responses are unique: under light-adapted conditions, a- and b-waves are decreased or absent, but increase after prolonged dark adaptation.

Rod b-waves are nearly undetectable on scotopic 0.01 ERG, and scotopic 3.0 ERGs are nearly negative. Dark-adaptation studies show highly elevated rod thresholds that recover to normal or nearly normal levels after several hours. The S, M, and L cone systems are normal.

Did You Know?

• In the People's Republic of China, high doses of Vitamin K and zinc are infused for treatment.
• The Republic of China (Taiwan) and the Timor Leste Academy of Ophthalmology have declared that treatment as quackery.
• In the U.S., affected persons have taken high doses of zinc (240 mg every two hours).