nyctalopia

   Also known as moonblink and night blindness. The term nyctalopia comes from the Greek words nux (night), alaos (blind), and ops (eye). The first known reference is found in the book Epidemics of the Hippocratic Corpus. In the Hip-pocratic Corpus, as well as in the Anglo-Saxon literature, the term nyctalopia is characterized as an impairment of nocturnal vision due to defective dark adaptation, while the affected individual's vision in bright light remains unaffected. Nyctalopia is usually classified as an *entoptic phenomenon. Pathophysiologically, it is associated primarily with a loss or impairment of rod photoreceptor function. Etiologically, it is associated primarily with a variety of acquired conditions such as vitamin A deficiency, retinitis pigmentosa, Usher's syndrome, and cancer-associated retinopathy. The condition may also be congenital, as in X-linked congenital stationary night blindness. Conceptually, nyctalopia constitutes the logical counterpart of * hemeralopia (i.e. day blindness). In the continental European literature (notably the French, Italian, and Greek literature) the term nyctalopia is used to denote a relative improvement of vision at night. This paradoxical connotation was noted by the physician Galen of Pergamum, born as Claudius Galenus (129-c. 216), who wrote, "Nyctalopia is the condition when someone can see neither in the moon's light nor in the light of lanterns... but so also call a disease where the opposite is observed, namely to see better at night than the day. Some confirm that the word that describes night blindness is also used for these patients, so that eventually the word describes two kinds of diseases: the disease where we do not see at night and the one where we do not see during the day." It has been suggested that the connotation of day blindness was prompted by an alternative etymology in which the term nyctalopia translates as night vision (from the Greek words nux (night) and ops (eye)). Apparently, in some European countries this version turned out to be the more influential one. Nevertheless, it would seem advisable to adhere to the original connotation of nyctalopia as a defective dark adaptation, or, alternatively, to use the term night blindness.

   References

   Brouzas, D., Charakidas, A., Vasilakis, M., Nikakis, P., Chatzoulis, D. (2001). Nyctalopia in antiquity: A review of the ancient Greek, Latin, and Byzantine literature. Ophthalmology, 108, 1917-1921.

   Ohba, N., Ohba, A. (2006). Nyctalopia and hemeralopia: The current usage trend in the literature. British Journal of Ophthalmology, 90, 1548-1549.