Night blindness is not only inconvenient, but it can be dangerous – especially if you try to drive a car after dark. The official medical term for this condition is nyctalopia, a condition that makes it difficult to see at night and when the lights are dim. It also makes it hard to focus when moving from a well lit room to one with less light. What causes night blindness?
What Causes Night Blindness?
The most common cause of night blindness is disease involving the retina in the back of the eye. The retina is made up of two types of light-sensitive cells – rods and cones. Cones are better suited for seeing color and detail, and they function best when there’s plenty of light. Rods come into play when light is dim since they’re more sensitive to low-light conditions. Blindness at night usually means the rods in the retina aren’t working properly.
Causes of Difficulty Seeing at Night: Retinitis Pigmentosa
Retinitis pigmentosa is a hereditary eye condition that causes gradual visual loss due to destruction of the rods and cones in the retina. The rods are usually affected first, so, not surprisingly, one of the first symptoms of retinitis pigmentosa is difficulty seeing at night. Over time, this progresses to dimming of daylight vision and tunnel vision. Sadly, some people progress to complete blindness. An ophthalmologist can diagnose this disease by looking for characteristic damage to the retina on eye exam.
Nutritional Causes of Blindness at Night
A deficiency of vitamin A causes difficulty seeing at night, and when it’s severe, complete night blindness. The rods contain a pigment called rhodopsin that’s necessary for night vision – and vitamin A is required to regenerate enough rhodopsin to see in dim light. Vitamin A deficiency isn’t common in this country, but people who have intestinal malabsorption problems, alcoholics, and vegetarians are at higher risk. This type of blindness at night is correctable with vitamin A supplements.
A Common Cause of Night Blindness with Aging: Cataracts
Cataracts are caused by protein build-up behind the lens of the eye. These protein deposits cloud the lens making it difficult to see at night and causing cloudy daytime vision. Fortunately, cataracts can be treated, so this is a potentially reversible cause of night blindness. Cataracts can be diagnosed through an exam by an ophthalmologist.
Other Causes of Blindness at Night
Untreated nearsightedness can cause difficulty seeing at night and problems adapting to dim light. Correcting nearsightedness with glasses will improve this type of night blindness. Night blindness can also occur from birth due to various genetic conditions. Some medications such as quinine, Accutane, and glaucoma medications, which constrict the pupil, also make it difficult to see at night. Finally, other conditions that affect the retina such as diabetic retinopathy and macular degeneration can cause partial or complete blindness at night.
What Causes Night Blindness?
Night blindness has a variety of causes, but, in all cases, it’s important to get a complete eye exam to find out why. Don’t forget to see your eye doctor regularly – especially if you have blindness at night.
Merck Manual. Eighteenth edition. 2006.
Web MD. “Eye Health and Night Blindness”