**2. Epidemiology**

The epidemiology data of dry eye symptom (DES) reveal that it affects from 5 to 35% of the population. Such discrepancy in the assessment of the frequency of the DES occurrence might be the effect of using different dry eye definitions in each of the studies, as well as the research being performed on different ethnic populations. The data given by the Women's Health Study indicate that Hispanics and Asians display greater predisposition to more severe symptoms of dry eye than Caucasians [2]. The incidence of Sjögren's syndrome, in which DES is a dominant symptom, may also be underestimated. There are no accurate records on the prevalence of this disease, with its milder course prone to be undiagnosed [3,4]. It is estimated that pSS occurs in 0.1–3.0% of the general population. The disease is more common for women (female/male ratio 9:1), affecting mainly individuals between the age of 40 and 60, with the disease most frequently occurring around 50 years of age [5].
