Many doctors recommend them, but fish oil supplements failed to help people with dry eye when put to a scientific test.
About 14 percent of U.S. adults have dry eye, which causes pain and vision problems. It's more common in women and with age, and is related to inflammation.
Omega-3 fatty acids in fish oil may reduce inflammation, so doctors thought they might help more than the artificial tears, eyedrops and other treatments patients use now.
A federally funded study gave 500 people daily doses of fish oil or dummy capsules. After one year, dry eye symptoms were similar in both groups.
Results were discussed Friday at a conference in Washington and published by the New England Journal of Medicine.