Dry eye disease is defined as “a multifactorial disease of the tears and ocular surface that results in symptoms and discomfort, visual disturbance, and tear instability with potential damage to the ocular surface. It is accompanied by increased osmolarity of the tear and inflammation of the ocular surface.”
1 Patients suffering from dry eye typically show symptoms like irritation, photophobia, burning, or a general discomfort. Moreover, they have an elevated risk of corneal infection potentially resulting in irreversible tissue damage.
2 The prevalence of dry eye syndrome is rapidly increasing; and in Western countries, more than 6% of the population over the age of 40 suffer from dry eye and more than 15% of people aged 65 years and older.
3 In Asian populations, an incidence of even 21% to 50% has been detected,
4–6 thus reflecting the varying vulnerabilities for dry eye in different ethnic groups. Two main subclasses contributing to dry eye have been identified: deficiency of the aqueous phase (tear deficiency) and alteration of the lipid layer composition.
2 The deficiency of the lipid layer leads to an increased evaporation of fluid (evaporative dry eye), thus considerably increasing the tear turnover rate as well as the osmolarity of tears.
7 The diagnosis of dry eye syndrome, and especially the subclassification of dry eye patients, remains complicated. Several factors, for example tear osmolarity,
8–10 the concentration of cytokines,
11–13 and the occurrence of protein glycosylation patterns,
14 have been a focus as tools for diagnostic purposes in dry eye. Also, alterations of the tear proteome have been the subject of several studies in the context of dry eye, as is also the case for other ocular surface–affecting diseases, such as Sjögren's syndrome,
15 meibomian gland disease (MGD),
16 pterygium,
17 allergy,
18 and diabetes.
19