Maternal Night Blindness: A New Indicator of Vitamin A Deficiency

N ight blindness—the inability to see after dusk or at night—is the most common ocular manifestation of moderate to severe vitamin A deficiency. Poor dark adaptation leading to night blindness occurs when there is decreased production of a vitamin A–dependent photosensitive pigment, rhodopsin, in the retinal receptors responsible for seeing under low levels of illumination (rods). Normally, when these photoreceptor cells are stimulated by light, rhodopsin is transformed, initiating neural signals that are transmitted to the brain, resulting in vision in dim illumination. In vitamin A deficiency, less rhodopsin is transformed and the level of light needed for vision rises. This results in delayed dark adaptation or, when sufficiently severe, in night blindness. Where prevalent, night blindness may be known by local terms that refer to evening or twilight blindness or, in some cultures, to “chicken eyes” or “chicken blindness” (chickens lack rod cells).