Retinitis Pigmentosa (RP) is a group of related diseases in which vision is affected as the light-sensitive cells at the back of the eye - the rod and cone cells - become damaged. The symptoms gradually worsen over time, and the nature of symptoms depends on which cells are affected. Some people find their central vision relatively good whereas others find their central vision diminishes, but their peripheral vision remains unaffected.  The speed at which the vision deteriorates varies from one person to another.