Night blindness is a condition in which a person is unable or less able to see under dark or subdued light. Furthermore, it refers a state in which the eye takes longer than usual to become accustomed to darkness.

Night blindness is a sign of number of eye diseases. Its origination is linked with the fashion in which the eye takes delivery of light rays. Light reaches the retina at the rear end of the eye passing through the Cornea and the Lens. The retina has specific nerve cells called photoreceptors. These photoreceptors translate the light rays into electrical signals; these signals are than conveyed to the brain for the formation of an image.

Rods and cones are two varieties of photoreceptors; millions of them are present in the eye, around 3 million rods and 100 million cones. The rods and the cones are of almost identical pattern with an exception of a smaller outer segment in the latter. The light-sensitive photo pigments are present in the outer segment of photoreceptors. The shape and form of these photo pigments changes when light rays reach them.

Vision under reduced illumination is facilitated by rods which are propagated all through the retina while the centrally located cones take care of the eyesight in bright light. The sight in low illumination is indistinct because of the linking brain and the mutually connected photoreceptors and the nerve cells. The brain cannot make out precisely which rod produced the signal as every rod share this linking to the brain with other rods. On the other hand, every cone is individually linked to the brain. So, everything is clearly visible in bright light as the brain can easily tell which cone on retina has produced signal.

Causes & symptoms
• Cataracts.
• Congenital night blindness.
• Liver conditions.
• Macular degeneration .
• Retinitis pigmentosa.
• Vitamin A deficiency
• Xerophthalmia.
• Zinc deficiency