Night Blindness also called nyctanopia and nyctalopia is a disorder in which a person has difficulty seeing in dim light or in adapting to darkness after bright light.

Causes:

• Vitamin A Deficiency is the main cause of night blindness. Normally, vitamin A in the eye's retina combines with a protein to form a compound known as rhodopsin, or visual purple. This compound enables the retina's light perceiving cells, the rod cells to be stimulated by light rays. When these cells contain too little rhopdosin, more light is needed to stimulate them.
• Night blindness may also occur as a result of various diseases like cataracts, retinitis pigmentosa that causes degeneration of the rods of the retina.
• Congenital night vision disorder

Prevention: Night blindness can be prevented by taking vitamin A in pill form or by drinking and eating foods such as milk, liver, eggs, spinach, malunggay leaves, carrots, and apricots. These foods are rich in either vitamin A or the pigment Beta-carotone, which is converted by the liver into vitamin A.

Treatments: Night blindness is treated with vitamin A, orally or by intramuscular injection. Normal vision is usually restored quickly.

Diagnostic tests for Night Blindness:

• General diagnosis which looks for obvious signs of malnourishment which suggests vitamin A deficiency.
• Visual acuity test. This test is used to determine the smallest letters a person can read on a standardized chart or card held 14 - 20 feet away.

• Visual field examination. The purpose of this test is to measure the peripheral (side) vision or visual field of the patient. The term visual field refers to the area of a scene you can see with your eyes fixed on one location. For example, while watering the plant in the garden, you may also notice your dog playing near you. Your peripheral vision enables you to see what your dog is doing.

• Ophthalmoscopy and slit lamp test to examine the optic nerve, macula and retina.