The tear film covers and lubricates the cornea, the bulbar conjunctiva and the palpebral conjunctiva. It maintains ocular surface health and protects the ocular surface from mechanical forces during blinking. The tear film is important in terms of nutrition of the cornea, and enables a smooth layer over the cornea surface to maintain the best optical quality of the otherwise irregular epithelial surface of the cornea (Paulsen 2013). In all, 15–30% of adults suffer from ocular-related symptoms such as stinging, burning, light sensitivity and blurry vision – a group of symptoms often associated with dry-eye syndrome (Begley et al. 2002; Caffery et al. 1998; Doughty et al. 1997; Shimmura et al. 1999). Dry eye is a multifactorial disease resulting in damage to the ocular surface and symptoms of discomfort, and principally is due to an insufficient tear film (Lemp et al. 2007). This insufficiency is typically caused by an aqueous deficiency or increased evaporation of the tear film (Lemp et al. 2007). This results in the core mechanism of dry eye, which is driven by tear fluid hyperosmolarity and tear film instability. Tear fluid hyperosmolarity appears to be the central mechanism here; however, in some forms of dry eye, tear film instability may be the initiating event (Lemp et al. 2007).

However, correlations between dry-eye symptoms and clinical signs are frequently poor (Hay et al. 1998; Nichols et al. 2004b; Schein et al. 1997). Nevertheless, this lack of relation between signs and symptoms might be due to limitations in the techniques of observation. The classically available methods of tear film evaluation are often invasive, with a lack of accuracy and repeatability (Savini et al. 2008).

This review attempts to discuss limitations of traditional tear film tests and to highlight advantages and disadvantages of recently introduced non-invasive methods for tear film assessment.