| Hemeralopia | |
|---|---|
| Specialty | Ophthalmology  |
Hemeralopia orday blindness is the inability to see clearly in bright light and is the exact opposite ofnyctalopia (night blindness), the inability to see clearly in low light.[1] It is also calledheliophobia.[2] It can be described as insufficientadaptation to bright light.
In hemeralopia, daytimevision gets worse, characterised by photoaversion (dislike/avoidance of light) rather thanphotophobia (eye discomfort/pain in light), which is typical of inflammations of the eye. Nighttime vision largely remains unchanged due to the use ofrods as opposed tocones (during the day), which are affected by hemeralopia and in turn degrade the daytime optical response. Hence, many patients feel they see better atdusk than in daytime.
The wordhemeralopia comes from theGreekημέρα hemera, "day", andαλαός alaos, "blindness".Hemera was theGreek goddess ofday, andNyx 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]
Hemeralopia is known to occur in several ocular conditions.Cone dystrophy andachromatopsia, affecting the cones in the retina, and the anti-epileptic drugtrimethadione are typical causes.Adie's pupil, which fails to constrict in response to light;aniridia, which is absence of the iris; andalbinism, where the iris is defectively pigmented, may also cause this. Centralcataracts, due to the lens clouding, disperses the light before it can reach theretina and is a common cause of hemeralopia and photoaversion in the elderly.Cancer-associated retinopathy (CAR), seen when certain cancers incite the production of deleterious antibodies against retinal components, may cause hemeralopia.
Another known cause is a rare genetic condition calledCohen syndrome (aka Pepper syndrome). Cohen syndrome is mostly characterized by obesity, mental retardation and craniofacialdysmorphism due to genetic mutation atlocus 8q22–23. Rarely, it may have ocular complications such as hemeralopia, pigmentarychorioretinitis,optic atrophy or retinal/iriscoloboma, having a serious effect on the person's vision.
Yet another cause of hemeralopia is uni- or bilateral postchiasmatic brain injury.[3] This may also cause concomitant nyctalopia.[3]
People with hemeralopia may benefit fromsunglasses. Wherever possible, environmental illumination should be adjusted to comfortable level.[3] Light-filtering lenses appear to help in people reportingphotophobia.[3]
Otherwise, treatment relies on identifying and treating any underlying disorder.
The protagonist of the Bollywood movieAankh Micholi suffers from this condition, which results in some hilarious incidents.