Nyctalopia
Encyclopedia
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 (for example, a lack of vitamin A
). It can be described as insufficient adaptation
to darkness.
The most common cause of nyctalopia is retinitis pigmentosa
, a disorder in which the rod cells in the retina
gradually lose their ability to respond to the light. Patients suffering from this genetic condition have progressive nyctalopia and eventually their daytime vision may also be affected. In X-linked congenital stationary night blindness
, from birth the rods either do not work at all, or work very little, but the condition doesn't get worse.
Another cause of night blindness is a deficiency of retinol, or vitamin A, found in fish oils, liver and dairy products. In the Second World War disinformation was used by the British to cover up the reason for their pilots' successful nighttime missions. Their success was, in the disinformation, attributed to improved night vision and pilots flying night missions were encouraged to eat plenty of carrots, which contain carotenoids and can be converted into retinol. The real reason for their success was their use of advanced radar
technologies.
The opposite problem, the inability to see in bright light, is known as hemeralopia
and is much rarer.
The outer area of the retina is made up of more rods than cones. The rod cells are the cells that enable us to see in poor illumination. This is the reason why loss of peripheral vision
often results in night blindness. Individuals suffering from night blindness not only see poorly at night, but also require some time for their eyes to adjust from brightly lit areas to dim ones. Contrast vision may also be greatly reduced.
Refractive "vision correction" surgery is a widespread cause of nyctalopia due to the impairment of contrast sensitivity function (CSF) which is induced by intraocular light-scatter resulting from surgical intervention in the natural structural integrity of the cornea.
, writing ca. 30 AD, described night blindness and recommended an effective dietary supplement: "There is besides a weakness of the eyes, owing to which people see well enough indeed in the daytime but not at all at night; in women whose menstruation is regular this does not happen. But success sufferers should anoint their eyeballs with the stuff dripping from a liver whilst roasting, preferably of a he-goat, or failing that of a she-goat; and as well they should eat some of the liver itself."
Historically, nyctalopia, also known as moonblink, was a temporary night blindness believed to be caused by sleeping in moonlight in the tropics.
in horses with leopard spotting
patterns, such as the Appaloosa
. It is present at birth (congenital), not sex-linked, non-progressive and affects the animal's vision in conditions of low lighting. CSNB is usually diagnosed based on the owner's observations, but some horses have visibly abnormal eyes: poorly-aligned eyes (dorsomedial strabismus) or involuntary eye movement (nystagmus). In horses, CSNB s has been linked with the leopard complex
color pattern since the 1970s. A 2008 study theorizes that both CSNB and leopard complex
spotting patterns are linked to the TRPM1
gene. The gene to which Lp has now been localized encodes a protein that channels calcium ion
s, a key factor in the transmission of nerve impulses. This protein, which is found in the retina and the skin, existed in fractional percentages of the normal levels in homozygous Lp/Lp horses.
Injury
-By cause:*Traumatic injury, a body wound or shock produced by sudden physical injury, as from violence or accident*Other injuries from external physical causes, such as radiation injury, burn injury or frostbite*Injury from infection...
or malnutrition (for example, a lack of vitamin A
Vitamin A
Vitamin A is a vitamin that is needed by the retina of the eye in the form of a specific metabolite, the light-absorbing molecule retinal, that is necessary for both low-light and color vision...
). 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 darkness.
The most common cause of nyctalopia is retinitis pigmentosa
Retinitis pigmentosa
Retinitis pigmentosa is a group of genetic eye conditions that leads to incurable blindness. In the progression of symptoms for RP, night blindness generally precedes tunnel vision by years or even decades. Many people with RP do not become legally blind until their 40s or 50s and retain some...
, a disorder in which the rod cells in 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...
gradually lose their ability to respond to the light. Patients suffering from this genetic condition have progressive nyctalopia and eventually their daytime vision may also be affected. In X-linked congenital stationary night blindness
X-linked congenital stationary night blindness
X-linked congenital stationary night blindness is a rare X-linked non-progressive retinal disorder. It has two forms, complete, also known as type-1 , and incomplete, also known as type-2 , depending on severity. In the complete form , there is no measurable rod cell response to light, whereas...
, from birth the rods either do not work at all, or work very little, but the condition doesn't get worse.
Another cause of night blindness is a deficiency of retinol, or vitamin A, found in fish oils, liver and dairy products. In the Second World War disinformation was used by the British to cover up the reason for their pilots' successful nighttime missions. Their success was, in the disinformation, attributed to improved night vision and pilots flying night missions were encouraged to eat plenty of carrots, which contain carotenoids and can be converted into retinol. The real reason for their success was their use of advanced radar
Radar
Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...
technologies.
The opposite problem, the inability to see in bright light, is known as hemeralopia
Hemeralopia
Hemeralopia is the inability to see clearly in bright light and is the exact opposite of Nyctalopia . 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...
and is much rarer.
The outer area of the retina is made up of more rods than cones. The rod cells are the cells that enable us to see in poor illumination. This is the reason why loss of peripheral vision
Peripheral vision
Peripheral vision is a part of vision that occurs outside the very center of gaze. There is a broad set of non-central points in the field of view that is included in the notion of peripheral vision...
often results in night blindness. Individuals suffering from night blindness not only see poorly at night, but also require some time for their eyes to adjust from brightly lit areas to dim ones. Contrast vision may also be greatly reduced.
Refractive "vision correction" surgery is a widespread cause of nyctalopia due to the impairment of contrast sensitivity function (CSF) which is induced by intraocular light-scatter resulting from surgical intervention in the natural structural integrity of the cornea.
Causes
- Vitamin A deficiency
- retinitis pigmentosaRetinitis pigmentosaRetinitis pigmentosa is a group of genetic eye conditions that leads to incurable blindness. In the progression of symptoms for RP, night blindness generally precedes tunnel vision by years or even decades. Many people with RP do not become legally blind until their 40s or 50s and retain some...
- congenital night blindness
- Sorsby's fundus dystrophy
- pathological myopia
- peripheral cortical cataract
- oguchi diseaseOguchi diseaseOguchi disease, also called congenital stationary night blindness, Oguchi type 1 or Oguchi disease 1, is an autosomal recessive form of congenital stationary night blindness associated with fundus discoloration and abnormally slow dark adaptation....
- refractive surgery (RK, PRK, LASIK)
Historical usage
Aulus Cornelius CelsusAulus Cornelius Celsus
Aulus Cornelius Celsus was a Roman encyclopedist, known for his extant medical work, De Medicina, which is believed to be the only surviving section of a much larger encyclopedia. The De Medicina is a primary source on diet, pharmacy, surgery and related fields, and it is one of the best sources...
, writing ca. 30 AD, described night blindness and recommended an effective dietary supplement: "There is besides a weakness of the eyes, owing to which people see well enough indeed in the daytime but not at all at night; in women whose menstruation is regular this does not happen. But success sufferers should anoint their eyeballs with the stuff dripping from a liver whilst roasting, preferably of a he-goat, or failing that of a she-goat; and as well they should eat some of the liver itself."
Historically, nyctalopia, also known as moonblink, was a temporary night blindness believed to be caused by sleeping in moonlight in the tropics.
Nyctalopia with animals
Congenital stationary night blindness is also an opthalmologic disorderOphthalmology
Ophthalmology is the branch of medicine that deals with the anatomy, physiology and diseases of the eye. An ophthalmologist is a specialist in medical and surgical eye problems...
in horses with leopard spotting
Leopard (pattern)
Leopard is a term used to describe a spotted color pattern, particularly in the hair coat or skin of animals, but also used to describe spotting patterns in plants and fabrics...
patterns, such as the Appaloosa
Appaloosa
The Appaloosa is a horse breed best known for its colorful leopard-spotted coat pattern. There is a wide range of body types within the breed, stemming from the influence of multiple breeds of horses throughout its history. Each horse's color pattern is genetically the result of various spotting...
. It is present at birth (congenital), not sex-linked, non-progressive and affects the animal's vision in conditions of low lighting. CSNB is usually diagnosed based on the owner's observations, but some horses have visibly abnormal eyes: poorly-aligned eyes (dorsomedial strabismus) or involuntary eye movement (nystagmus). In horses, CSNB s has been linked with the leopard complex
Leopard complex
The leopard complex is a group of genetically-related coat patterns in horses. These patterns range from progressive increases in interspersed white hair similar to graying or roan to distinctive, Dalmatian-like leopard spots on a white coat. Secondary characteristics associated with the leopard...
color pattern since the 1970s. A 2008 study theorizes that both CSNB and leopard complex
Leopard complex
The leopard complex is a group of genetically-related coat patterns in horses. These patterns range from progressive increases in interspersed white hair similar to graying or roan to distinctive, Dalmatian-like leopard spots on a white coat. Secondary characteristics associated with the leopard...
spotting patterns are linked to the TRPM1
TRPM1
Transient receptor potential cation channel subfamily M member 1 is a protein that in humans is encoded by the TRPM1 gene.- Function :The protein encoded by this gene is similar to the transient receptor potential calcium channel family members...
gene. The gene to which Lp has now been localized encodes a protein that channels calcium ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
s, a key factor in the transmission of nerve impulses. This protein, which is found in the retina and the skin, existed in fractional percentages of the normal levels in homozygous Lp/Lp horses.