A healthy fat found in fish oil (docosahexaenoic acid, or DHA), may slow the rate of vision loss in people with an eye disease known as retinitis pigmentosa (RP). RP is a group of diseases that affect the retina, leading to night blindness, tunnel vision, and possible total blindness. DHA is necessary for proper vision development. People with RP have lower levels of DHA in the blood than people without the disease.

In a recent study, researchers looked at a form of the disease that only affects males and how DHA might affect its progression. Forty-one people completed the four-year trial. The participants were randomly assigned to take either 400 mg of DHA from fish oil per day or a placebo.

The researchers found that those taking DHA had over two times more DHA in the blood than the placebo group. Overall, the rate of disease progression was not statistically different between the two groups; however, among the group that took DHA, those people who had the highest DHA blood levels had a slower rate of disease progression. DHA also significantly reduced the rate of rod loss in boys younger than 12 years old, and preserved cone function in those who were 12 years or older.

The researchers feel the results are encouraging for people with RP, as some benefit was associated with taking DHA. They also point out that the amount of DHA used in this study was relatively small, and that much higher doses have been used to treat other diseases, such as rheumatoid arthritis and psoriasis. They encourage further studies using larger amounts of DHA.

American Journal of Ophthalmology 2004;137:704– 18