Could you explain what is retinitis pigmentosa?

Retinal degeneration: The retina lines the back of our eye and acts like the film of a camera. It "sees" the light. Retinitis pigmentosa (rp) is a group of diseases caused by defective genes that cause the retina to malfunction. It is most often inherited. Over time patients lose peripheral and then central vision from rp. There is no treatment but in some cases vitamins can slow its course. There is no cure.

Retinitis pigmentosa: Retinitis pigmentosa (rp) is a group of inherited disorders characterized by progressive peripheral vision loss and night vision difficulties that can eventually lead to central vision loss.