We don't want to leave you in the dark about nychtalopia.
Nyctalopia is night blindness. Vision in nychtalopia is abnormally impaired in dim light and in the dark.
Nychtalopia is due to decreased function of specific vision cells, namely the rods, in the retina.
Night blindness is a classic finding of vitamin A deficiency. It was first described by the English physician William Heberden (1710-1801).
Heberden discovered other medical disorders of importance including angina pectoris and Heberden's nodes. Angina pectoris is chest pain that is often severe and crushing. It is due to a poor supply of oxygen to the heart muscle. Heberden's nodes are nodules in and about the last joint of the finger. They are a sign of osteoarthritis of the small joints.
The word "nychtalopia" emanates from Greek roots: "nyct" (night) + "aloas" (obscure or blind) + "opsis" (vision) = nightblind vision.
Nychthemeron is an allied word. It is from "nycht" (night) + "hemera" (day) and is the full 24-hour period of a night and a day. For example, to understand the behavior of babies, one must study them throughout the nychthemeron, an opportunity often afforded by babies to new parents.
In addition to nychtalopia, many other wondrous words and tantalizing terms are tucked away in MedicineNet's Medical Dictionary.