Night blindness, also known as nyctalopia, is the inability to acclimatize to dim lighting conditions. Some people become more nearsighted at night as the pupil dilates in dark conditions, a condition called spherical aberration. When a person is unable to see well enough to distinguish distinct images in low lighting conditions, night blindness results.

People with night blindness (also called impaired dark adaptation) have poor vision in the darkness, but see normally when adequate light is present.

Night blindness is mostly a symptom of several underlying diseases or conditions, especially untreated nearsightedness.

This occurs because an individual with myopia will become even more nearsighted as the pupil dilates at night. On the other hand, patients being treated with glaucoma medications, which constrict the pupil, will also frequently have night blindness, because the small pupil allows minimal light to enter the eye. Retinitis pigmentosa, a retinal degenerative disorder, may also be associated with night blindness. Some other less common causes of night blindness include the retinal disorders such as gyrate atrophy.

Types of night blindness -

• Congenital stationary night blindness - This type of night blindness, present at birth, is mostly due to inherited disorders.

• Progressive night blindness – This type of night blindness continues to gradually worsen over time.

Causes can include a myriad of factors such as retinol or vitamin A deficiency, any disease, and toxic effects of drugs like quinine.

• Night Blindness due to complication of obesity related surgery - Individuals who undergo obesity surgery can develop night blindness, mainly because important nutrients such as vitamin A may be lacking if patients fail in the intake of nutritional supplements following surgery.

What are the causes of Night Blindness?

Night blindness is caused due to a disorder of the cells in the retina of the eye, which are responsible for vision in dim light. This may be caused due to:

• Nearsightedness.

• Glaucoma medications that work by constricting the pupil.

• Presence of cataracts.

• Retinitis pigmentosa - a retinal degenerative disorder

• Vitamin A deficiency

• Malabsorption - if it affects vitamin A absorption

• Celiac disease

• Cystic fibrosis

• Bile duct obstruction

• Diabetes

• Macular degeneration

• Birth defect

What are the symptoms of night blindness?

Common symptoms include difficulty in vision when driving in the evening or at night, poor vision in reduced light, and feeling that the eyes take longer to "adjust" to seeing in the dark.

Associated symptoms include:

# Dry eyes

# Blurred vision

How is Night Blindness treated?

Treatment for night blindness will depend upon its cause. Treatment may be quite simple as a new prescription eyeglasses or changing glaucoma medications, or it may be complex requiring surgery in cases of cataracts.

If night blindness is caused by nearsightedness, the patient may need to wear glasses at night. Night blindness if caused by a loss of some of the function of the rods, then a visual field examination is performed. Tests would need to be performed to determine whether the receptor cells in the retina are functioning properly, or if the problem is somewhere else. But most times there's nothing that can be done if these cells are damaged.

If a doctor determines that there is simply a need for vitamin A to help the night blindness, then that would be recommended. For those patients who have retinitis pigmentosa, vitamin A is being used to help.

Thus, treatments for night blindness include:

# Vitamin A supplements

# Treatment of any underlying cause

Vitamins that may be helpful in case of night blindness -

Night blindness may be an early sign of Vitamin A deficiency. Such a deficiency may result due to a diet low in animal foods, such as eggs, dairy products, meat and fish. Low intake of fruits and vegetables containing beta-carotene, such as carrots, mango, spinach, sweet potato, which the body converts into vitamin A, may also contribute to a vitamin A deficiency. Doctors often recommend Vitamin A dietary supplements per day to correct a deficiency. Beta-carotene is less successful at correcting vitamin A deficiency than vitamin A itself, because it is not relatively well-absorbed into the body, and is only slowly converted by the body into vitamin A.

Zinc deficiency in diet is common, and a lack of zinc may reduce the activity of retinol dehydrogenase - the enzyme needed to help vitamin A work in the eye. Zinc is helpful in people whose night blindness is caused due to zinc-deficiency; therefore, many doctors suggest 15 to 30 mg of zinc per day to support healthy vision. As long-term zinc supplementation may reduce copper levels in the body, 1 to 2 mg of copper per day is also recommended for people who are on zinc supplements for more than a few weeks