The purpose of this study is to evaluate the efficacy and safety of oral valproic acid to slow the progression of visual function and/or to improve the visual function in patients with retinitis pigmentosa (RP).

Enrolled subjects in valproic acid group will be treated with oral valproic acid 500mg daily for 48 weeks. Visual function and safety will be assess before and after treatment (48 weeks) between valproic acid and control groups.

This study is designed as a single-site, interventional, prospective, non-randomized, controlled study of 200 participants. Patients that participate in the study will be assigned to either valproic acid group or control in a 3:1 ratio.

Inclusion Criteria:

• Diagnosis of retinitis pigmentosa (RP) established by night blindness, visual field constriction, marked reduction of electroretinogram, and the clinical signs of RP in fundus examination
• Best corrected visual acuity of 20/200 or more on a Snellen chart in at least one eye
• Intact visual field of 5 or more as measured by the kinetic perimetry
• Understand and sign the IRB-approved informed consent document for the study
• Body weight: male (40 kg to 100 kg), female (40 kg to 80 kg)
• Must be able to swallow tablets
• Female subjects of childbearing potential must commit to practice acceptable methods of contraception

Exclusion Criteria:

• Pregnant women
• Lactating mothers
• Medical problems that make consistent follow-up over the treatment period unlikely (e.g., stroke, myocardiac infarction, malignancy) or severe systemic disease
• Other ocular disease: retinal disease other than RP or cystoid macular edema, glaucoma, cataract worse than +2PSC or infectious corneal disease
• Coagulation disorder or bleeding-tendency
• Liver dysfunction
• Renal dysfunction
• History of pancreatitis
• History of neurological disorders including epilepsy, history of brain injury or any organic brain disorders
• History of mental disorders including schizophrenia, bipolar disorder, or suicidality
• Currently receiving valproic acid or other anti-convulsants
• Has taken one of the following drugs at least 4 weeks prior to enrollment as these drugs are specifically known to affect the progression of RP: vitamin A, lutein, omega-3 fatty acid, or any antioxidant which affect the blood flow of retina or retinal function.