Hemeralopia (from

Greek Greek may refer to: Greece 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 ...

''ημέρα'' hemera, "day", and ''αλαός'' alaos, "blindness") is the inability to see clearly in bright light and is the exact opposite of

nyctalopia Nyctalopia (; ), also called night-blindness, is a condition making it difficult or impossible to see in relatively low light. It is a symptom of several eye diseases. Night blindness may exist from birth, or be caused by injury or malnutrition ( ...

(night blindness), the inability to see clearly in low light.

Hemera In Greek mythology, Hemera (; grc, Ἡμέρα, Hēméra, Day ) was the personification of day. According to Hesiod, she was the daughter of Erebus (Darkness) and Nyx (Night), and the sister of Aether. Though separate entities in Hesiod's '' ...

was the

Greek goddess A major branch of classical mythology, Greek mythology is the body of myths originally told by the ancient Greeks, and a genre of Ancient Greek folklore. These stories concern the origin and nature of the world, the lives and activities of de ...

day A day is the time period of a full rotation of the Earth with respect to the Sun. On average, this is 24 hours, 1440 minutes, or 86,400 seconds. In everyday life, the word "day" often refers to a solar day, which is the length between two ...

, and

Nyx Nyx (; , , "Night") is the Greek goddess and personification of night. A shadowy figure, Nyx stood at or near the beginning of creation and mothered other personified deities, such as Hypnos (Sleep) and Thanatos (Death), with Erebus (Darkn ...

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 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 po ...

to bright light. It is also called "heliophobia" and "day blindness". 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 of ...

(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 A cone is a three-dimensional geometric shape that tapers smoothly from a flat base (frequently, though not necessarily, circular) to a point called the apex or vertex. A cone is formed by a set of line segments, half-lines, or lines conn ...

(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, enou ...

than in daytime.

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 r ...

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 a ...

, affecting the cones in the retina, and the anti-epileptic drug trimethadione are typical causes.

Adie's pupil Adie syndrome, also known as Holmes-Adie syndrome, is a neurological disorder characterized by a tonically dilated pupil that reacts slowly to light but shows a more definite response to accommodation (i.e., light-near dissociation). It is fre ...

, which fails to constrict in response to light;

aniridia Aniridia is the absence of the iris, a muscular structure that opens and closes the pupil to allow light into the eye. It is also responsible for eye color. Without it, the central eye appears all black. It can be congenital, in which both ey ...

, 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 pink or blue eyes. Individuals with the condition are referred to as albino. Varied use and interpretation of the term ...

, 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. Cataracts often develop slowly and can affect one or both eyes. Symptoms may include faded colors, blurry or double vision, halos around light, trouble ...

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

retina The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which the ...

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 Locus (plural loci) is Latin for "place". It may refer to: Entertainment * Locus (comics), a Marvel Comics mutant villainess, a member of the Mutant Liberation Front * ''Locus'' (magazine), science fiction and fantasy magazine ** ''Locus Award' ...

8q22–23. Rarely, it may have ocular complications such as hemeralopia, pigmentary

chorioretinitis Chorioretinitis is an inflammation of the choroid (thin pigmented vascular coat of the eye) and retina of the eye. It is a form of posterior uveitis. If only the choroid is inflamed, not the retina, the condition is termed choroiditis. The ophtha ...

, optic atrophy or retinal/iris

coloboma A coloboma (from the Greek , meaning defect) is a hole in one of the structures of the eye, such as the iris, retina, choroid, or optic disc. The hole is present from birth and can be caused when a gap called the choroid fissure, which is presen ...

, 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.

References

{{DEFAULTSORT:Hemeralopia Visual disturbances and blindness

Causes

Management

See also

References