TEARS

Tears are a saline secretion produced by the lacrimal glands and several accessory glands that coat the surface of the eye, forming the tear film. The tear film consists of three layers: a superficial lipid layer that reduces evaporation, a thick aqueous layer that provides moisture and nutrients, and a mucin-containing layer that helps the film adhere to the ocular surface.

Tears are produced in three forms: basal tears for continuous lubrication; reflex tears triggered by irritants such as smoke, wind, or foreign bodies; and emotional tears associated with crying, which occur in response to psychological states and social cues.

Anatomy and drainage: The main lacrimal glands, located in the upper outer region of the orbit, secrete the aqueous component of tears; additional glands (Krause and Wolfring) contribute mucous and lipid components. Tears drain through tiny puncta on the eyelid margins into the canaliculi, converge on the lacrimal sac, and pass through the nasolacrimal duct into the nasal cavity.

Composition: Tears are primarily water but also contain electrolytes, enzymes such as lysozyme, lactoferrin, and peroxidases, lipids from the meibomian glands, mucins, and secretory IgA antibodies. This combination supports lubrication, protection against infection, debris removal, and surface health.

Functions and clinical relevance: Tears lubricate and protect the ocular surface, wash away debris, supply nutrients and antioxidants, and help maintain a smooth optical surface. Tear production can be influenced by environmental conditions, health status, and age. Reduced production can cause dry eye, while blockage of drainage can result in excessive tearing (epiphora). Emotional tears are linked to social and emotional processes, and may differ in content from other tear types.