Introduction
visual disability, death, retinal degeneration, RP
RETINAL DEGENERATION, RETINITIS PIGMENTOSA (RP)
Retinitis pigmentosa (RP) is a slowly progressive, inherited, rod-cone retinal degeneration in which early rod photoreceptor death is typically followed by cone photoreceptor death, causing significant visual disability in most patients (The concept of the first trial (1984–1991), testing vitamin A and vitamin E supplementation to slow the progression of RP, was initially inspired by positive reports from patients who independently started taking one or both supplements (The original results of the trial, that vitamin A supplementation slowed the progression of RP by 1.7% per year, and that vitamin E caused faster progression by 1.8% per year, were not met with uniform agreement (The original investigators did look for potential differential treatment responses among the genetic subtypes, which at the time were defined as recessive, dominant, X-linked, or unknown, based on pedigree analysis and limited molecular genetic solutions. No differential treatment responses were identified using these categories (