Tears are a clear liquid secreted by the lacrimal glands, structures located above each eye. They are composed of water, electrolytes, proteins, lipids, and mucins, forming a complex fluid film covering the eye’s surface. This tear film is essential for eye health, protecting the ocular surface, and enabling clear vision. The human body produces three types of tears, each with specialized functions.
Basal Tears
Basal tears are continuously present on the eye’s surface as a thin, protective layer. These tears are produced by accessory lacrimal glands and typically secreted at a rate of approximately 2 microliters per minute. Their primary role involves lubricating the eyes and providing a smooth optical surface for light to refract onto the retina.
They also deliver essential nutrients and oxygen to the cornea, a transparent tissue that lacks blood vessels. Basal tears contain proteins such as lysozyme and lactoferrin, along with electrolytes like sodium and potassium, which contribute to their antibacterial properties. This constant flow also clears small particles and debris from the eye surface.
Reflex Tears
Reflex tears are produced in greater volume as an immediate, involuntary response to irritants or stimuli. These tears are typically triggered by external factors such as foreign particles entering the eye, exposure to smoke or dust, or strong odors like those released from cutting onions. Bright lights or even physical injury to the eye can also stimulate their production.
Their main function is to flush out irritants from the eye’s surface. They serve as a rapid defense against environmental threats. Reflex tears are generally more watery in consistency compared to basal tears and contain higher concentrations of antibodies, including immunoglobulins, which combat potential infections introduced by irritants.
Emotional Tears
Emotional tears are linked to intense emotional states. These tears can arise from both positive feelings, such as joy, relief, or happiness, and negative emotions, including sadness, grief, stress, or physical pain. The production of emotional tears involves the limbic system and hypothalamus, areas of the brain associated with emotional processing.
Emotional tears exhibit a unique chemical composition, containing higher levels of stress hormones such as prolactin, adrenocorticotropic hormone (ACTH), and leucine enkephalin, a natural painkiller. They may also contain elevated concentrations of manganese and potassium. One theory suggests that the release of these hormones through emotional tears helps regulate the body’s stress response, contributing to a sense of relief or catharsis after crying. Furthermore, emotional tears serve a social purpose, communicating distress or vulnerability to others, which can elicit empathy, support, and foster social bonding.