Impairment of the vision normally possible in dim light is called night
blindness, or nyctalopia. It may be an early sign
of
vitamin A deficiency, because that vitamin plays a major role in the cells of the eye sensitive to dim light. Night
blindness is also a manifestation of various eye disorders such as glaucoma and optic nerve disease. It is often the earliest symptom of retinitis pigmentosa, a chronic and progressive inflammation of the retina. One form of the condition, called congenital stationary night blindness, is hereditary.
Treatment of night blindness is aimed at treating the underlying disorder. For vitamin deficiency, use of vitamin tablets or a diet rich in the pigments called carotenoids can help restore night vision.