Tears
Tears are a complex fluid with biological and symbolic roles.
Tears are the clear fluid produced by the lacrimal glands, which are found in the eyes of most land mammals, though some species have reduced or absent lacrimal glands. Based on how they are made, tears fall into three categories: basal, emotional, and reflex. Normally, about 0.5 to 2.2 microliters of tears are secreted each minute, but irritation can boost that rate by roughly a hundred times, up to around 300 microliters per minute. Tears consist of water, electrolytes, proteins, lipids, and mucins, arranged in layers on the eye’s surface, and the makeup of each tear type differs significantly.
Tears serve several roles: they lubricate the eyes (basal tears), flush out irritants (reflex tears), and help the immune system. They also appear as part of the body’s natural pain response. Emotional tears may have a biological purpose, with some hypotheses suggesting they excrete stress hormones that build up during emotional distress. Beyond physiology, tears carry symbolic meaning for humans.
**Physiology**
**Chemical composition** In 1946, Wolff described the tear film using a slit lamp as having three layers: lipid, aqueous, and mucous. Tears are made of water, salts, antibodies, and lysozymes (antibacterial enzymes). Each layer’s composition determines its function—for instance, the diverse lipid classes in the tear film lipid layer (TFLL) give it unique physicochemical properties that help form a thin film and prevent it from collapsing onto the eye’s surface. More recently, Mazyar Yazdani at Oslo University Hospital suggested that the TFLL might also aid corneal oxygenation, based on its composition-driven traits.
The composition shifts among tear types. Tears from emotional reactions differ chemically from those caused by irritants like onion fumes, dust, or allergens. A contested hypothesis proposes that emotional tears may contain higher levels of stress hormones such as adrenocorticotropic hormone and leucine enkephalin (a natural painkiller), hinting that they help balance stress hormone levels.
**Drainage of tear film** The lacrimal glands secrete lacrimal fluid, which travels through main excretory ducts into the space between the eyeball and eyelids. Blinking spreads this fluid across the eye’s surface. The fluid collects in the lacrimal lake, located at the inner corner of the eye. The lacrimal papilla, a small elevation on the inner eyel
- types
- basal, emotional, reflex
Lore & Background
Tears are produced by the lacrimal glands (present in most land mammals, though some species have reduced or absent lacrimal glands) and spread across the eye during blinking. They drain through the lacrimal punctum, sac, and nasolacrimal duct into the nasal cavity. The tear film was described in 1946 by Wolff as having a three-layered structure: lipid, aqueous, and mucous. More recently, Mazyar Yazdani at Oslo University Hospital proposed that the tear film lipid layer may contribute to corneal oxygenation.
The composition of tears varies by type. A contested hypothesis suggests that emotional tears may contain higher concentrations of stress hormones such as adren
Reader's Guide
Tears hold significance across biology and human culture. Biologically, they lubricate the eyes, remove irritants, aid the immune system, and occur as part of the body's natural pain response. Emotional tears may excrete stress-inducing hormones built up during emotional distress. The trigeminal nerve (V1) carries sensory pathways for tear reflexes, while the great petrosal nerve from cranial nerve VII provides autonomic innervation to the lacrimal gland.
In human culture, crying is associated with tears and strong emotional impetuses, varying from sadness to joy. Social norms around crying differ: some cultures consider it undignified, while in most Western cultures it is more acceptable for women and children to cry than men. Tears also have symbolic significance, such as in the phrase 'crocodile tears' for insincere grief, which also refers to Bogorad's syndrome—a condition where faulty nerve regeneration after Bell's palsy causes tearing while eating.
Pathological conditions involving tears include keratoconjunctivitis sicca (dry eye disease), familial dysautonomia (lack of overflow tears during emotional crying), and pseudobulbar affect (episodic uncontrollable crying). Treatment for dry eyes includes eye-drops with methyl cellulose or carboxy-methyl cellulose, and for meibomian gland dysfunction, intense pulsed light therapy.
Did You Know?
- The basal rate of tear secretion is approximately 0.5–2.2 μL/min, and irritation can increase secretion by up to 100-fold to about 300 μL/min.
- A contested hypothesis suggests that emotional tears may contain higher concentrations of stress hormones such as adrenocorticotropic hormone and leucine enkephalin, though this is not yet confirmed.
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