Imagine how scary it would be, as a teen or young adult, to be told that you were slowly going blind. Now imagine how relieved you would be to learn that two common nutrients could help you hang onto your sight well into old age.

Well, that’s the happy news from Harvard researchers who studied the progressive eye disease retinitis pigmentosa (RP). With this condition, the light-sensitive retina (which converts images to electrical signals and sends them via the optic nerve to the brain) slowly loses the ability to do its job. RP sufferers typically report night blindness in adolescence…loss of side vision in young adulthood…tunnel vision with advancing age…and in some cases, blindness by age 60.

The new study drew on data from earlier clinical trials in which RP patients took a supplement of vitamin A palmitate (not beta-carotene) at 15,000 international units (IU) daily for four to six years. They also filled out yearly questionnaires about their dietary habits. That initial research revealed that vitamin A supplementation helped to slow the rate of decline of retinal function across the whole retina, as shown by a test called an electroretinogram. For the new study, the researchers further analyzed the data on 357 RP patients who were taking vitamin A to see whether their intake of omega-3 fatty acids had any effect on their disease.

Findings: Compared with RP patients who consumed less than 200 mg of omega-3s daily, those whose diets included 200 mg or more per day of omega-3s experienced a 40% slower rate of decline in their distance central vision. The study authors also noted that, in their earlier research, the vitamin A/omega-3 combination helped preserve some side vision, too.

Based on this evidence, the researchers made an encouraging projection. A typical RP patient who starts by age 35 to supplement with 15,000 IU per day of vitamin A palmitate and eats an omega-3-rich diet—for instance, one or two three-ounce servings per week of cold-water oily fish (such as salmon, mackerel, herring, tuna or sardines)—could, on average, gain 18 additional years of relatively preserved central vision. That would be enough to keep her seeing fairly well for most if not all of her life.

RP patients: Even if you’re already older than 35, it’s worthwhile to talk to your ophthalmologist to see whether this nutritional treatment is safe and appropriate for you. Do not self-treat—researchers noted that this dose of vitamin A is not appropriate for children under age 15, people with liver disease or women who are or plan to become pregnant.