1. Medical problems that make consistent follow-up over the treatment period unlikely (e.g. stroke, severe MI, end stage malignancy), or in general a poor medical risk because of other systemic diseases or active uncontrolled infections.
2. Other retinal diseases: Glaucoma, retinal inflammatory disease, (Note: CME is allowable), cataract worse than +2 NS or herpes simplex virus of the eye.
3. Intact visual field of 5° or less with measurable kinetic field on the V4e, III4e, or I4e isopters.
4. Subject unable to provide reliable perimetry measurements in both eyes for both static and kinetic visual field, as determined by the Reading Center.
6. History of cancer (other than non-melanoma skin cancer) diagnosed or requiring treatment within the last 2 years.
7. A hemoglobin concentration, a platelet count or an absolute neutrophil count below the lower limit of normal at study entry. The limits of normal are defined by each site and are agreed to by the medical monitor
8. Suspected liver dysfunction determined by having alanine aminotransferase (ALT), aspartate aminotransferase (AST) and bilirubin values elevated above the upper limit of normal.
9. History of pancreatitis by clinical features and/or laboratory abnormalities in the last 12 months.
10. Renal dysfunction based on serum creatinine using the Modification of Diet in Renal Disease (MDRD) equation.
11. Urea cycle disorders.
12. History of neurological conditions including epilepsy, history of brain injury, encephalitis, or any organic brain syndrome.
13. History of schizophrenia, schizoaffective disorder, bipolar disorder, suicidal or organic mental disorders.
14. Currently receiving valproic acid or other anti-convulsants.
15. Sensitive to or have ever had an allergic reaction to valproic acid.
16. Sensitive to or have ever had an allergic reaction to peanuts as peanut oil is an inactive ingredient in valproic acid capsules and the placebo.
17. Has taken one of the following drugs at least 2 weeks prior to randomization as these drugs are specifically known to interact with valproic acid: aspirin (except that prophylactic use of ‘low-dose’ aspirin (less than or equal to 81 mg) is allowed),, felbamate, rifampin, amitriptyline/nortriptyline, carbamazepine, clonazepam, diazepam, ethosuximide, lamotrigine, phenobarbital, primidone, phenytoin, tolbutamide, warfarin, or zidovudine.
18. Pregnant women.
19. Lactating mothers who are breast feeding their babies.
20. RP patients involved in other clinical trials within the last 3 months.
21. Require enrollment by consent of a legally authorized representative.
22. Persons who are unable to read are not allowed to consent for themselves or others to participate in this study.
23. A potential participant cannot participate if he/she lives in the same household as a current participant in this protocol