Hemeralopia
Encyclopedia
Hemeralopia 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.
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.
and achromatopsia
, 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
, which is absence of the iris; Albinism
where the iris is defectively pigmented may also cause this. Cataract
s, due to the lens clouding, disperses the light before it can reach the retina
, is a common cause of hemeralopia and photoaversion in elderly. C.A.R (Cancer Associated Retinopathy) seen when certain cancers release deleterious antibodies against retinal structures, 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 postchiasmatic brain injury. This may also cause concomitant night blindness.
. Wherever possible, environmental illumination should be adjusted to comfortable level. Light-filtering lenses appears to help in people reporting photophobia
.
Otherwise, treatment relies on identifying and treating any underlying disorder.
Nyctalopia
Nyctalopia 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). Hemera
Hemera
In Greek mythology Hemera was the personification of day and one of the Protogenoi or primordial deities. She is the goddess of the daytime and, according to Hesiod, the daughter of Erebos and Nyx...
was the Greek goddess of day
Day
A day is a unit of time, commonly defined as an interval equal to 24 hours. It also can mean that portion of the full day during which a location is illuminated by the light of the sun...
and Nyx
Nyx
In Greek mythology, Nyx was the primordial goddess of the night. A shadowy figure, Nyx stood at or near the beginning of creation, and was the mother of personified gods such as Hypnos and Thánatos...
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
Adaptation (eye)
In ocular physiology, adaptation is the ability of the eye to adjust to various levels of darkness and light.-Efficacy:The human eye can function from very dark to very bright levels of light; its sensing capabilities reach across nine orders of magnitude. This means that the brightest and the...
to bright light.
In hemeralopia, daytime vision
Visual perception
Visual perception is the ability to interpret information and surroundings from the effects of visible light reaching the eye. The resulting perception is also known as eyesight, sight, or vision...
gets worse, characterised by photoaversion (dislike/avoidance of light) rather than photophobia
Photophobia
Photophobia is a 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 actual physical photosensitivity of the eyes, though the term...
(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
Dusk
Dusk is the beginning of darkness in the evening, and occurs after twilight, when the sky generally remains bright and blue. Civil dusk is when the earth has rotated enough that the center of the sun is at 6° below the local horizon...
than in daytime.
Causes
Hemeralopia is known to occur in several ocular conditions. Cone dystrophyCone 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....
and achromatopsia
Achromatopsia
Achromatopsia , is a medical syndrome that exhibits symptoms relating to at least five separate individual disorders. Although the term may refer to acquired disorders such as color agnosia and cerebral achromatopsia, it typically refers to an autosomal recessive congenital color vision disorder,...
, affecting the cones in the retina, and the anti-epileptic drug Trimethadione
Trimethadione
Trimethadione is an oxazolidinedione anticonvulsant. It is most commonly used to treat epileptic conditions that are resistant to other treatments.-Fetal trimethadione syndrome:...
are typical causes. Adie's pupil which fails to constrict in response to light; Aniridia
Aniridia
Aniridia is the absence of the iris. Aniridia usually involves both eyes. It can be congenital or caused by a penetrant injury. Isolated aniridia is a congenital disorder which is not limited to a defect in iris development, but is a panocular condition with macular and optic nerve hypoplasia,...
, which is absence of the iris; Albinism
Albinism
Albinism is a congenital disorder characterized by the complete or partial absence of pigment in the skin, hair and eyes due to absence or defect of an enzyme involved in the production of melanin...
where the iris is defectively pigmented may also cause this. Cataract
Cataract
A cataract is a clouding that develops in the crystalline lens of the eye or in its envelope, varying in degree from slight to complete opacity and obstructing the passage of light...
s, due to the lens clouding, disperses the light before it can reach the retina
Retina
The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...
, is a common cause of hemeralopia and photoaversion in elderly. C.A.R (Cancer Associated Retinopathy) seen when certain cancers release deleterious antibodies against retinal structures, may cause hemeralopia.
Another known cause is a rare genetic condition called Cohen Syndrome
Cohen syndrome
Cohen syndrome is believed to be a gene mutation at locus 8q22 gene COH1. Cohen syndrome has several characteristics such as obesity, mental retardation and craniofacial dysmorphism...
(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 postchiasmatic brain injury. This may also cause concomitant night blindness.
Management
People with hemeralopia may benefit from sunglassesSunglasses
Sunglasses or sun glasses are a form of protective eyewear designed primarily to prevent bright sunlight and high-energy visible light from damaging or discomforting the eyes. They can sometimes also function as a visual aid, as variously termed spectacles or glasses exist, featuring lenses that...
. Wherever possible, environmental illumination should be adjusted to comfortable level. Light-filtering lenses appears to help in people reporting photophobia
Photophobia
Photophobia is a 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 actual physical photosensitivity of the eyes, though the term...
.
Otherwise, treatment relies on identifying and treating any underlying disorder.