Tear-film osmolarity

Tear-film osmolarity is a physiological measurement of the concentration of solutes within the precorneal tear film, serving as a vital indicator of ocular surface health and stability [1, 10]. It is formally recognized by the Tear Film and Ocular Surface Society (TFOS) DEWS II report as a 'core mechanism' in the pathogenesis of Dry Eye Disease (DED), where hyperosmolarity (typically defined as ≥308 mOsm/L) triggers a 'vicious cycle' of inflammatory cytokine production, oxidative stress, and epithelial cell apoptosis [4, 8, 16]. Although not a specific protein or receptor, tear-film osmolarity is the primary physiological parameter that various therapies aim to normalize to restore homeostatic balance [6, 15]. Clinical management often involves the use of hypotonic eye drops to lower solute concentration or anti-inflammatory agents like cyclosporine and lifitegrast to mitigate the damage caused by hyperosmolar stress [5, 17]. Point-of-care monitoring of this parameter provides an objective, numerical biomarker for diagnosing disease severity and evaluating the efficacy of pharmacological treatments [7, 13].

Other names

Tear osmolarityHyperosmolarity of the tear filmTear-film osmolality

Pharmacological interventions aim to restore osmotic balance by either directly diluting the tear film with hypotonic lubricants or by increasing natural tear secretion and reducing the underlying inflammation that exacerbates evaporative loss [6, 8, 17].