Efficacy of nutritional supplementation with omega-3 and omega-6 fatty acids in dry eye syndrome: a systematic review of randomized clinical trials.

To critically appraise scientific evidence regarding the efficacy of nutritional supplementation with omega-3 and omega-6 fatty acids for the treatment of dry eye syndrome (DES). A systematic review of randomized clinical trials was performed. Two independent reviewers selected and analysed the scientific papers that met inclusion and exclusion criteria. Objective and subjective efficacy outcomes were assessed. The trials involved a total of 2591 patients in fifteen independent studies. All studies were published between 2005 and 2015. The supplements used were mostly omega-3 and omega-6 in different proportions. Subjective improvement was measured using mainly Ocular Surface Disease Index (OSDI) test and Dry Eye Severity Score (DESS) test: significant differences in favour of the experimental group were found in seven of the studies. The objective amelioration was assessed by lacrimal function parameters: Tear break-up time (TBUT) significantly increased in nine studies and Schirmer's test in four studies. We observed a discrete improvement in the parameters of tear function. Scientific evidence is not strong enough to systematically recommend the use of omega-3 and omega-6 fatty acids as a standalone treatment of DES independently from its aetiology. However, they could be considered as an effective alternative to topical treatment in patients with DES secondary to certain pathologies