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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.


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The Bill night sight is simply clipped on top of the day sight, with no need for bore-sighting.
THE crowds came back to Kempton yesterday when the familiar Boxing Day sight of packed stands and traffic jams returned to the racecourse and its surrounding roads, writes Lee Mottershead.
The day sight uses a small lens cap and the night sight takes a large lens cap.
DIOP) of Salem, New Hampshire for two thermal imaging products: the HH750 Hand-Held Thermal Imager and the TADS 850 Thermal Augmented Day Sight.