Further Evaluation of Docosahexaenoic Acid in Patients With RetinitisPigmentosa Receiving Vitamin A Treatment

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Abstract
We have reported elsewhere in this issue that oral supplementation withdocosahexaenoic acid in a dosage of 1200 mg/d did not, on average, slow therate of decline in ocular function over a 4-year interval among 208 patientswith retinitis pigmentosa who concurrently received vitamin A, 15 000IU/d.1 Among these patients randomly assignedto docosahexaenoic acid plus vitamin A (DHA + A group) or control fatty acidcapsules plus vitamin A (control + A group), about 70% reported taking vitaminA, 15 000 IU/d, prior to entry, whereas 30% did not; approximately equalnumbers of patients on and not on vitamin A prior to entry were in the DHA+ A and control + A groups. After 1 year of follow-up, we unexpectedly noteda highly significant statistical interaction between the effect of docosahexaenoicacid supplementation and the status of vitamin A intake prior to entry onchange in visual field sensitivity (P<.01), suggestingthe need for subgroup analyses. Therefore, we followed change in ocular functionin these 4 subgroups over the 3 remaining years of this trial. The presentarticle compares rates of decline in ocular function over 4 years among thesubgroups within the DHA + A and control + A groups defined by use or nonuseof vitamin A prior to entry.

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