MedTerms Medical Dictionary

Night blindness: Impaired vision in dim light and in the dark, due to impaired function of specific vision cells (namely, the rods) in the retina.

The ability of our eyes to quickly view objects as they shift from light to dark areas and the ability to see in dim light or at night is an important part of our visual health. When we are not able to do such, the condition is referred to commonly as night blindness or medically as nyctalopia. It occurs as a result of various diseases that cause degeneration of the rods of the retina (the sensory cells responsible for vision in dim light). The problem can also appear as an inherited deficiency in visual purple, or rhodopsin, which is the pigment of the rods of the retina. The abnormality can also result from vitamin A deficiency. Rhodopsin,  maintains its photosensitivity only in the presence of vitamin A.

Night blindness is a classic finding from deficiency of vitamin A. It was described by the English physician William Heberden (1710-1801) who also discovered other medical disorders of importance including angina pectoris (chest pain that is often severe and crushing, due to an inadequate supply of oxygen to the heart muscle) and osteoarthritis of the small joints with nodules (Heberden's nodes) in and about the last joint of the finger.

Sources of vitamin A include animal livers, milk, and yellow and green leafy vegetables which contain carotenes, chemically related substances that are converted to vitamin A in the body.

Night blindness is also called day sight, nocturnal amblyopia, nyctalopia and nyctanopia.

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