Pilot Study on the Effect of Vitamin A Supplementation on Cone Function in Retinitis Pigmentosa

Retinitis pigmentosa (RP) is a collective term for a group of inherited retinal dystrophies that are a major cause of irreversible blindness. RP of some type occurs in approximately 1 out of 3500 persons in the United States. Gene mutations are responsible for the majority of RP. To date, mutations have been identified in 30 different genes linked to RP. The visual prognosis of RP is poor, since the gradual but relentless visual field loss leads eventually to some degree of blindness. Although no effective treatment for RP has been identified, participants supplemented with a daily oral dose of 15,000 IU vitamin A palmitate have shown, on average, a slower rate of deterioration of retinal function when the intervention is continued over several years. The purpose of this research is to determine whether administration of high oral doses of vitamin A can acutely improve cone photoreceptor function in RP participants as measured by electroretinography (ERG). In this interventional, non-randomized, prospective, pilot study, 10 participants (five with the RHO1 gene mutation and five without the mutation) will receive a daily oral dose of 50,000 IU of vitamin A palmitate for 4 weeks, followed by a maintenance dose of 15,000 IU daily for the subsequent 2 weeks. The primary efficacy outcome is a relative percentage change in ERG response amplitude subsequent to vitamin A supplementation. A secondary efficacy outcome is a relative percentage change in implicit time from pre- to post- vitamin A supplementation, with improvement specified as a shorter response implicit time. Other secondary outcomes will be improvements in visual field (Humphrey 10-2; sum of thresholds). Safety outcomes include visual fields, ETDRS visual acuity, intraocular pressure, serum vitamin A level and liver function tests.