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. It is also called heliophobia. It can be described as insufficient

adaptation In biology, adaptation has three related meanings. Firstly, it is the dynamic evolutionary process of natural selection that fits organisms to their environment, enhancing their evolutionary fitness. Secondly, it is a state reached by the p ...

to bright light. In hemeralopia, daytime

vision Vision, Visions, or The Vision may refer to: Perception Optical perception * Visual perception, the sense of sight * Visual system, the physical mechanism of eyesight * Computer vision, a field dealing with how computers can be made to gain und ...

gets worse, characterised by photoaversion (dislike/avoidance of light) rather than

photophobia Photophobia is a medical symptom of abnormal intolerance to visual perception of light. As a medical symptom, photophobia is not a morbid fear or phobia, but an experience of discomfort or pain to the eyes due to light exposure or by presence o ...

(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 Dusk occurs at the darkest stage of twilight, or at the very end of astronomical twilight after sunset and just before nightfall.''The Random House College Dictionary'', "dusk". At predusk, during early to intermediate stages of twilight, enoug ...

than in daytime. The word ''hemeralopia'' comes from the

Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...

''ημέρα'' hemera, "day", and ''αλαός'' alaos, "blindness". Hemera was the Greek goddess of

day A day is the time rotation period, period of a full Earth's rotation, rotation of the Earth with respect to the Sun. On average, this is 24 hours (86,400 seconds). As a day passes at a given location it experiences morning, afternoon, evening, ...

, 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.

Causes

Hemeralopia is known to occur in several ocular conditions.

Cone dystrophy A cone dystrophy is an inherited ocular disorder characterized by the loss of cone cells, the photoreceptors responsible for both central and color vision. Presentation The most common symptoms of cone dystrophy are vision loss (age of onset ...

and

achromatopsia Achromatopsia, also known as rod monochromacy, is a medical syndrome that exhibits symptoms relating to five conditions, most notably monochromacy. Historically, the name referred to monochromacy in general, but now typically refers only to an aut ...

, affecting the cones in the retina, and the anti-epileptic drug trimethadione are typical causes. Adie's pupil, which fails to constrict in response to light;

aniridia Aniridia is a condition characterized by the absence or near absence of the iris, the colored, muscular ring in the eye that controls the size of the pupil and regulates the amount of light entering the eye. This absence results in a primarily b ...

, which is absence of the iris; and

albinism Albinism is the congenital absence of melanin in an animal or plant resulting in white hair, feathers, scales and skin and reddish pink or blue eyes. Individuals with the condition are referred to as albinos. Varied use and interpretation of ...

, where the iris is defectively pigmented, may also cause this. Central

cataracts A cataract is a cloudy area in the lens of the eye that leads to a decrease in vision of the eye. Cataracts often develop slowly and can affect one or both eyes. Symptoms may include faded colours, blurry or double vision, halos around ligh ...

, due to the lens clouding, disperses the light before it can reach the

retina The retina (; or retinas) is the innermost, photosensitivity, light-sensitive layer of tissue (biology), tissue of the eye of most vertebrates and some Mollusca, molluscs. The optics of the eye create a focus (optics), focused two-dimensional ...

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 called Cohen syndrome (aka Pepper syndrome). Cohen syndrome is mostly characterized by obesity, mental retardation and craniofacial dysmorphism due to genetic mutation at locus 8q22–23. Rarely, it may have ocular complications such as hemeralopia, pigmentary chorioretinitis, optic atrophy or retinal/iris coloboma, having a serious effect on the person's vision. Yet another cause of hemeralopia is uni- or bilateral post chiasmatic brain injury. This may also cause concomitant nyctalopia.

Management

People with hemeralopia may benefit from

sunglasses Sunglasses or sun glasses (informally called shades or sunnies; more names Sunglasses#Other names, below) are a form of Eye protection, protective eyewear designed primarily to prevent bright sunlight and high-energy visible light from damagin ...

. Wherever possible, environmental illumination should be adjusted to comfortable level.Page 96 in: Light-filtering lenses appear to help in people reporting

. Otherwise, treatment relies on identifying and treating any underlying disorder.

In popular culture

The protagonist of the Bollywood movie Aankh Micholi suffers from this condition, which results in some hilarious incidents.

References

{{DEFAULTSORT:Hemeralopia Visual disturbances and blindness

Causes

Management

In popular culture

See also

References