Polyunsaturated FAs show modest benefits for dry eye disease
Dry eye disease, also known as keratoconjunctivitis sicca (KS), commonly occurs in postmenopausal women, especially as they age. Many diseases and drugs can cause dry eye disease by altering the production or composition of tears, as well as producing abnormalities on the surface of the eye and eyelids.
Patients may complain of their eyes burning, a feeling of grittiness, and/or the sensation of a foreign body in their eyes. In addition to these complaints, patients may experience visual disturbances, and over time, inflammation and ulceration of the cornea may develop. Vision may be significantly reduced if dry eye disease remains untreated.
Causes and treatment
The prevalence of this condition is about 7% in women and 4% in men aged 50 and older.1 Although female sex and increasing age are important risk factors, smoking, dry environments, and diet may also contribute to its development. Dry eye syndromes are frequently part of autoimmune diseases such as Sjögren syndrome. Beta-blockers, preservatives used in some ophthalmic products, and drugs with anticholinergic properties can cause dry eye syndromes, as can natural products such as niacin, echinacea, and kava.
The diagnosis of dry eye disease is a complex process. Lacrimal duct functioning is assessed, along with the aqueous and mucin content of tear film. In addition, ocular epithelial cells and markers of inflammation are evaluated. The treatment of dry eye disease is based on the specific underlying etiology, although artificial tears remain a core therapy for most patients. Nonpharmacologic measures such as the use of humidifiers may be helpful. Natural products have been promoted for dry eye disease, with studies focusing on the use of essential fatty acids (FAs) containing eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), as well as the omega-6 FAs linoleic acid (LA) and gamma linoleic acid (GLA).
Three studies of patients with dry eye disease with different causes have evaluated the use of LA (57 mg to 224 mg daily) and GLA (30 mg to 300 mg daily). Although symptoms improved, more objective measures have demonstrated only modest and more variable effects. The mechanism by which omega-6 FAs might benefit the condition is unclear, as these substances traditionally were believed to be proinflammatory, although animal models have not shown this result. Supplements containing omega-3 FAs, including alpha linoleic acid (ALA), have also shown modest benefits. In animal models, an endogenous compound derived from EPA, resolvin E1, may be involved in the resolution of ocular inflammation.
Several studies of combination omega-3 and -6 FAs have shown modest effects. Of note, studies with FAs have used different patient populations, short durations, and varying amounts and sources of DHA, EPA, and GLA, making direct comparisons difficult.
Recently, in a 6-month study of moderate to severe KS, 38 patients were randomized to an oral daily supplement of black currant seed oil (1,570 mg containing 15% GLA and 12%–15% ALA), 170 mg of DHA plus EPA, and antioxidant vitamins or to matching placebo capsules. The commercial supplement used was HydroEyes. The study used the Ocular Surface Disease Index (OSDI) questionnaire and other clinical and biochemical assessments standard for the disease. At 12 weeks and 24 weeks, the OSDI scores in the active treatment group were significantly better than those of the placebo group. Several parameters appeared to worsen in the placebo group over the study period, including lid margin erythema, CD11c staining, HLA-DR staining, and one measure of corneal smoothness. The use of artificial tear solutions was similar in the two groups.
What to tell patients
Dry eye disease can be serious and should not be ignored. When the use of artificial tears increases, patients should be evaluated by their primary care provider or ophthalmologist. Taking FA supplements or adding fish oil to the diet may provide subjective benefits for dryness and eye pain. The optimal amount and type of FAs remain unknown.
Schaumberg DA, Sullivan DA, Buring JE, et al. Prevalence of dry eye syndrome among US women. Am J Ophthalmol. 2003;136(2):318–26.
Sheppard JD, Singh R, McClellan AJ, et al. Long-term supplementation with n-6 and n-3 PUFAs improves moderate to severe keratoconjunctivitis sicca: a randomized double-blind clinical trial [published online ahead of print, July 23, 2013]. Cornea.