discovering
dry eye
Nutraceuticals
and Dry Eye
BY KELLY K. NICHOLS,
OD, MPH, PHD
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.
Dosage Information
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.
Contact Lens Spectrum, Issue: June 2005