Nyctalopia

Nyctalopia
Other names	Night blindness
Effect of night blindness. Left: normal night vision. Right: night-blind vision.
Specialty	Ophthalmology

Nyctalopia (

Another cause of night blindness is a deficiency of retinol, or vitamin A₁, found in fish oils, liver, and dairy products.

The opposite problem, the inability to see in bright light, is known as hemeralopia and is much rarer.

Since the outer area of the retina is made up of more rods than cones, loss of peripheral vision often results in night blindness. Individuals with night blindness not only see poorly at night but also require extra time for their eyes to adjust from brightly lit areas to dim ones. Contrast vision may also be greatly reduced.

Rods contain a receptor-protein called rhodopsin. When light falls on rhodopsin, it undergoes a series of conformational changes ultimately generating electrical signals which are carried to the brain via the optic nerve. In the absence of light, rhodopsin is regenerated. The body synthesizes rhodopsin from vitamin A, which is why a deficiency in vitamin A causes poor night vision.

• Cataract (peripheral cortical)
• Certain medications, such as
  phenothiazines^[3]
• Choroideremia
• Chronic pancreatitis - Presumably due to malabsorption of vitamin A^[4]
• Glaucoma
• Oguchi disease
• Pathological myopia
• Refractive surgery (LASIK, photorefractive keratectomy, radial keratotomy)
• Retinal detachment
• Retinitis pigmentosa
• Sorsby's Fundus Dystrophy (Macular degeneration)
• Visual snow
• Vitamin A deficiency; often via xerophthalmia

Aulus Cornelius Celsus, writing ca. 30 AD, described night blindness and recommended an effective dietary supplement, liver being a good source of vitamin A: "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 while roasting, preferably of a he-goat, or failing that of a she-goat; and as well they should eat some of the liver itself."^{[citation needed]}

Historically, nyctalopia, also known as moonblink, was a temporary night blindness believed to be caused by sleeping in moonlight in the tropics.^[5]

In the French language, nyctalopie and héméralopie have inverse meanings, the first naming the ability to see in the dark as well as in plain light, and the second the inability to do so. It is thought that this inversion from Latin happened during the 2nd century AD,^[6] even though the Ancient Greek νυκτάλωψ (nuktálōps) has been used in both senses.

Night blindness, sometimes referred to as gravel, was occasionally documented during the American Civil War, particularly within the Confederate States of America. Like rheumatism, night blindness was viewed as a condition that could be easily faked or exaggerated and, initially, people with night blindness were regarded with some suspicion. Some soldiers who reported symptoms of nyctalopia also presented with symptoms of scurvy, suggesting a fundamental cause of poor nutrition.^[7]

Congenital stationary night blindness is also an