Night Blindness

Poor dark adaptation, rod system dysfunction

Overview

Night blindness, or nyctalopia, is difficulty seeing in dim light or adapting from bright to dark conditions. It is a symptom of dysfunction of the rod photoreceptors, which are responsible for vision in low light, or of conditions that reduce the light reaching the retina. Worldwide, vitamin A deficiency is a major cause, since vitamin A is needed to form rhodopsin, the light sensitive pigment of rods, and it remains a public health problem in some low income countries. Deficiency can also follow malabsorption or bariatric surgery. Inherited causes include retinitis pigmentosa, congenital stationary night blindness, choroideremia, and gyrate atrophy. Other contributors include cataract, advanced glaucoma, high myopia, and some medications. The link between night blindness and diet was recognized in antiquity, and ancient Egyptian medical texts describe liver as a remedy. Evaluation includes retinal examination, dark adaptation testing, and electroretinography, and treatment depends on the cause.