Retinitis pigmentosa is a rare inherited disease which affects the photoreceptors of the retina. These cells (rods and cones) absorb the light energy and transmit the signal to other retinal cells, until the signal reaches special parts of the brain.

This disease affects mostly one type of photoreceptors, which are called rods and are activated at night and at mesopic conditions (low light conditions). Some gene's mutation leads to gradual death of the photosensitive cells and thereby cause loss of the peripheral visual field initially and later on loss of central vision also.

We can distinguish retinitis pigmentosa in two subcategories:

• Type 1: Night blindness early (children at the age of 10), due to rods cells loss and as a result, it leads to peripheral vision loss.
• Type 2: Night blindness appears at the adulthood and is characterized by loss of rods as well as cones sensitivity.