What is "hemeralopia"

Hemeralopia \Hem`e*ra*lo"pi*a\, n. [NL., fr. Gr. ?, the opposite of ?; ? day + ? of ?. See Nyctalopia.] (Med.) A disease of the eyes, in consequence of which a person can see clearly or without pain only by daylight or a strong artificial light; day sight.

Note: Some writers (as Quain) use the word in the opposite sense, i. e., day blindness. See Nyctalopia.

n. (context medicine English) The inability to see clearly in bright light; day blindness

n. inability to see clearly in bright light [syn: day blindness]

Hemeralopia (from Greek ημέρα, hemera "day"; and αλαός, alaos "blindness") is the inability to see clearly in bright light and is the exact opposite of nyctalopia (night blindness). Hemera was the Greek goddess of day and Nyx was the goddess of night. However, it has been used in an opposite sense by many non-English-speaking doctors. It can be described as insufficient adaptation to bright light. It is also called heliophobia and day blindness.

In hemeralopia, daytime vision gets worse, characterised by photoaversion (dislike/avoidance of light) rather than photophobia (eye discomfort/pain in light) which is typical of inflammations of eye. Nighttime vision largely remains unchanged due to the use of rods as opposed to cones (during the day), which are affected by hemeralopia and in turn degrade the daytime optical response. Hence many patients feel they see better at dusk than in daytime.