Further evaluation of docosahexaenoic acid in patients with retinitis pigmentosa receiving vitamin A treatment: Subgroup analyses

Abstract

Objective: To determine whether docosahexaenoic acid will slow the course of retinal degeneration in sub-groups of patients with retinitis pigmentosa who are receiving vitamin A. Design: A cohort of 208 patients with retinitis pigmentosa, aged 18 to 55 years, were randomly assigned to 1200 mg of docosahexaenoic acid plus 15000 IU/d of vitamin A given as retinyl palmitate (DHA + A group) or control fatty acid plus 15000 IU/d of vitamin A (control + A group) and followed up over 4 years. Seventy percent of the patients in each group were taking vitamin A, 15000 IU/d, prior to entry. We compared rates of decline in ocular function in the DHA + A vs control + A groups among the subgroups defined by use or nonuse of vitamin A prior to entry. We also determined whether decline in ocular function was related to red blood cell phosphatidylethanolamine docosahexaenoic acid level, dietary ω-3 fatty acid intake, or duration of vitamin A use. Main outcome measures were Humphrey Field Analyzer visual field sensitivity, 30-Hz electroretinogram amplitude, and visual acuity. Results: Among patients not taking vitamin A prior to entry, those in the DHA + A group had a slower decline in field sensitivity and electroretinogram amplitude than those in the control + A group over the first 2 years (P=.01 and P=.03, respectively); these differences were not observed in years 3 and 4 of follow-up or among patients taking vitamin A prior to entry. In the entire cohort, red blood cell phosphatidylethanolamine docosahexaenoic acid level was inversely related to rate of decline in total field sensitivity over 4 years (test for trend, P=.05). This was particularly evident over the first 2 years among those not on vitamin A prior to entry (test for trend, P=.003). In the entire control + A group, dietary ω-3 fatty acid intake was inversely related to loss of total field sensitivity over 4 years (intake, <0.20 vs ≥0.20 g/d; P=.02). The duration of vitamin A supplementation prior to entry was inversely related to rate of decline in electroretinogram amplitude (P=.008). Conclusions: For patients with retinitis pigmentosa beginning vitamin A therapy, addition of docosahexaenoic acid, 1200 mg/d, slowed the course of disease for 2 years. Among patients on vitamin A for at least 2 years, a diet rich in ω-3 fatty acids (≥0.20 g/d) slowed the decline in visual field sensitivity.