Hemeralopia

Hemeralopia
Specialty	Ophthalmology

Hemeralopia or day blindness is the inability to see clearly in bright light and is the exact opposite of nyctalopia (night blindness), the inability to see clearly in low light.^[1] It is also called heliophobia.^[2] It can be described as insufficient adaptation to bright light.

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 the 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.

The word hemeralopia comes from the Greek ημέρα hemera, "day", and αλαός alaos, "blindness". Hemera was the Greek goddess of day, and Nyx was the goddess of night. Hemeralopia has been used to describe night blindness rather than day blindness by many non-English-speaking doctors, causing confusion.^[1]