Definition of Amblyopia, nocturnal

Amblyopia, nocturnal: Amblyopia refers to blindness so nocturnal amblyopia is, literally, night blindness. Listed in medical dictionaries under "Nyctalopia" from the Greek nyct (night) + aloas (obscure or blind) + opsis (vision), the condition
involves impaired vision in dim light and in the dark due
to impaired function of specific vision cells (namely, the rods)
in the retina.
Night blindness, a classic finding in vitamin A deficiency, was discovered by the English physician William Heberden (1710-1801). (Heberden also described other medical disorders of importance including angina
(chest pain that is often severe and crushing, due to an
inadequate supply of oxygen to the heart muscle) and Heberden's
nodes, bumps around the small joints due to osteoarthritis.)
Night blindness (nyctalopia) is also called day sight and
nyctanopia.

Amblyopia: Partial or complete loss of vision in one eye caused by conditions that affect the normal development of vision. These conditions include strabismus, in which the eyes are crossed inward (esotropia) or turned outward (exotropia) and anisometropia, in which there is a major difference in refractive error between the two eyes from nearsightedness, farsightedness, or astigmatism. Less common causes of amblyopia include ptosis (drooping) of one eyelid, disease of the cornea (preventing light from entering the eye), congenital cataract, and injury to the eye of a young child.
In amblyopia, the brain favors one eye over the other. The other eye is ignored. It is not adequately stimulated and the visual brain cells do not mature normally. Amblyopia is the most common cause of monocular blindness, partial or complete blindness in one eye. Amblyopia affects 2 to 3% of children in the US.
Treatment of strabismus may involve surgical correction of the eye muscle imbalance. In the case of severe refractive error, it should be corrected by glasses, contact lenses or, if appropriate, lasix. Wearing an eye patch over the stronger eye is a hallowed treatment for amblyopia. Another option is atropine eye drops to blur the vision temporarily in the stronger eye. Weekend atropine provides an improvement in visual acuity of a magnitude similar to that provided by daily atropine in treating moderate amblyopia.
The term "amblyopia" is sometimes incorrectly used interchangeably with lazy eye. "Amblyopia" is made up of ambly- from the Greek "amblys" meaning blunt, dull, faint, or dim and -opia from the Greek "ops" meaning eye, and refers to vision, so amblyopia is literally dim vision.
See also: Anisometropia: Nocturnal amblyopia; Strabismus.