**1. Introduction**

Sjögren's syndrome (SS) is a rheumatic autoimmune disease in which exocrine glands (salivary and lacrimal glands) are involved that results in clinical symptoms of dry mouth and dry eye. For the first time, SS-like clinical condition was described by Mikulicz in 1892 [1]. However, the disease was fully described (clinically and histopathology) later by the Swedish ophthalmologist Henrik Sjögren in 1930. He detected coincidence of rheumatism and hyposecretion of lacrimal and salivary glands and introduced the new term *keratoconjunctivitis sicca* to describe significant conjunctival and corneal staining with both dyes: methylene blue and rose bengal [1–3]. He also compared keratoconjunctivitis sicca and xerophthalmia seen in vitamin A deficiency and postulated that these cases represented a systemic disease. His doctoral thesis on this problem did not receive recognition and the author was disqualified from receiving PhD. Though his academic career was over, he lived on the day when the disease was named after him [2].

SS affects the exocrine glands; lymphocytic infiltration leads to sicca syndrome of the eyes, oral cavity, pharynx, larynx, and/or vagina [1, 3–6]. Systemic manifestations of SS are divided into visceral (lung, heart, kidney, endocrine, nervous system, gastrointestinal) and non-visceral (skin, myalgia, arthralgia). The risk of lymphoma is higher in patients with SS than in general population [1, 4, 6–8]. SS can be primary-pSS (without any other accompanying symptoms) or secondarysSS (with other autoimmune diseases: systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), polyarteritis nodosa, systemic sclerosis, granulomatosis with polyangiitis (GPA), primary biliary cholangitis (PBC), mixed connective tissue disease, occult thyroid eye disease) [1, 3–6, 9–11].

Dry eye disease (DED) problems are involved in diagnostic criteria of SS as an important part of diagnosis. Patients with DED seek medical help for many years prior to SS diagnosis—about 25% of DED patients have an underlying rheumatic condition, commonly pSS. Only one-third of patients with SS carried final diagnosis prior to ocular symptoms [1, 11, 12]. Some studies demonstrated coincidence of DED and SS in 46.7% cases [1, 11].
