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McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



night blindness, a visual disorder manifested by partial or total inability to see objects in the twilight or at night.

Nyctalopia may arise in connection with certain organic diseases of the retina, choroid coat, or optic nerve, or with glaucoma (symptomatic nyctalopia); in connection with poor general nutrition due to starvation, certain liver diseases, malaria, alcoholism, or other conditions accompanied by a deficiency or total absence of vitamin A (functional nyctalopia); or in connection with congenital pigment degeneration of the retina (congenital nyctalopia). The immediate cause of nyctalopia is connected with structural changes in the retinal rods or a deficiency of rhodopsin (visual purple), which disintegrates in the light but is restored in the dark in the presence of vitamin A. Nyctalopia patients suffer from photophobia in bright light and sharply reduced vision in the twilight and at night. They may also suffer from reduced color sensitivity with respect to blue and yellow. Sometimes their visual field is narrowed and its acuity diminished. Nyctalopia is usually exacerbated in early spring because of insufficient vitamin A in the food.

A fully balanced diet, cod liver oil, and intake of vitamins A, B1, B2, and C are important to both treatment and prevention. In cases of symptomatic nyctalopia the causative disease should be treated.


Katsnel’son, A. B. Vitaminy i avitaminozy v oftal’mologii.[Cheliabinsk] 1947.


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
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The day sight cap screws onto the sight servo housing.
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The gunner is provided with a self-stabilised day sight and a periscope-mounted second-generation thermal camera for night work, with an integral eye-safe laser rangefinder.
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The unit drops onto the existing day sight without any further adjustment.
While the laser rangefinder is said to considerably diminish stress on the gunner, the image intensifier module (which can be rapidly swapped for the day sight) has an illuminated reticle with adjustable brightness.