Night blindness. Listed in medical dictionaries under "Nyctalopia" from the Greek "nyct' (night) + "aloas" (obscure or blind) + "opsis" (vision), the condition involves impaired vision in dim light and in the dark (but normal sight in bright light), due to impaired function of specific vision cells (the "rods") in the retina. Day sight (night blindness) is a classic symptom resulting from deficiency of vitamin A.