Nutraceuticals and Dry Eye
There has been increasing interest in the use of omega-3 fatty acids as supplemental treatment for dry eye. Anecdotally, my patients and colleagues continue to report "success stories" with the addition of supplemental omega-3 fatty acids to the diet, especially with regard to improvements related to lens wear.
The Facts About Fatty Acids
The essential fatty acids (EFAs) alpha-linoleic acid (ALA) and linoleic acid (LA) play a role in human nutrition. The body doesn't produce these naturally, so we obtain them from food. EFAs are vital to the structure of cell membranes and have many important roles in the body.
Recently, nutrition experts have placed increased emphasis on the ratio of omega-6 (n-6) to omega-3 (n-3) fatty acids in the diet. They've suggested that the average ratio of n-6 to n-3 in the American diet is 12:1, whereas the recommended ratio is approximately 4:1 (Health Canada) or 5:1 (US Institute of Medicine). For comparison, the n-6 to n-3 ratio of flax (seed) is 0.3:1, while corn oil has a ratio of 58:1.
The Effect of Inflammation
Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), both omega-3 fatty acids, convert into anti-inflammatory prostaglandins and leukotrienes, which help decrease inflammation and pain. In contrast, arachadonic acid, the inflammatory cascade precursor, is a metabolism byproduct of the omega-6 fatty acid pathway. Therefore, maintaining a low ratio of omega-6 to omega-3 may result in less inflammatory mediators in the body.
If dry eye has an inflammatory component, then reduction of inflammatory mediators on the ocular surface through increased consumption of omega-3 fatty acids may result in a more stable tear film, with or without a contact lens. It's unknown whether we can measure EFAs (or metabolism byproducts) in the lipid layer of the tear film. The impact of finding these fatty acids in the tears or on a lens following lipid deposition is unknown.
Experts have suggested that the daily intake of ALA is approximately 1g to 1.5g; however many clinical studies have used higher doses (5g to 25g). Scientists have proposed that by increasing your intake of omega-3 fatty acids and reducing the omega-6 fatty acids consumed, you'll naturally bring the ratio of omega-3 and omega-6 fatty acids back into a healthier balance.
Does it Work?
The FDA doesn't regulate nutritional supplements, funding for projects related to supplements is limited and dose standardization is speculation at best. If you recommend omega fatty acids to your patients, remember that research is limited in this area and that a large range in quality of supplements may exist.
Dr. Nichols is assistant professor of clinical optometry at The Ohio State University College of Optometry in the area of dry eye research.