Night blindness

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Overview

Nyctalopia refers to night blindness or difficulty of the eye in visualizing under dim light or at night. Daytime vision, however, is unimpaired. Nyctalopia is due to the eye's inability to adapt quickly from lightness to darkness. The principle cell-type associated with Nyctalopia is rod cells. Rods are a type of photoreceptor cell present in the retina that transmits low-light vision and is most responsible for the neural transmission of nighttime sight. Rods have a singular photopigment, rhodopsin, which utilizes the protein scotopsin and the Vitamin A-derived cofactor, retinol. This cascade is essential for the body's ability to regulate the pupillary light reflex. The pupillary light reflex allows unilateral afferent detection of changes in light energy entering the eye, and efferent adjustments in the pupillary sphincter and dilator pupillae muscles to initiate consensual constriction and dilation of the eyes. Pupil dilation is an adaptive response to changes in lightness and darkness. Night blindness is the physical manifestation of impaired functioning of these processes.

Symptoms

Abnormal trouble adapting to the dark while driving at night.

Blurry vision when driving in the dark.

Difficulty seeing in places with dim lighting, like your house or a movie theater.

Excessive squinting at night.

Trouble adjusting from bright areas to darker ones.

Causes

A few eye conditions can cause night blindness, including:

nearsightedness, or blurred vision when looking at faraway objects

cataracts, or clouding of the eye’s lens

retinitis pigmentosa, which occurs when dark pigment collects in your retina and creates tunnel vision

Usher syndrome, a genetic condition that affects both hearing and vision

Older adults have a greater risk of developing cataracts. They’re therefore more likely to have night blindness due to cataracts than children or young adults.

In rare cases in the United States or in other parts of the world where nutritional diets may vary, vitamin A deficiency can also lead to night blindness.

Vitamin A, also called retinol, plays a role in transforming nerve impulses into images in the retina. The retina is a light-sensitive area in the back of your eye.

Risk factors

Myopia (nearsightedness).

Glaucoma medications that work by constricting the pupil.

Cataracts.

Retinitis pigmentosa.

Vitamin A deficiency, especially in individuals who have undergone intestinal bypass surgery.

Diabetes.

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Complications

Although night blindness adversely affects a person's ability to see in dim light, it does not cause complete blindness. It may create problems seeing road signs while driving at night. It may also take longer time than usual for the eye to adapt when going from light to dark settings.

Prevention

You can't prevent night blindness that's the result of birth defects or genetic conditions, such as Usher syndrome. You can, however, properly monitor your blood sugar levels and eat a balanced diet to make night blindness less likely.