“It is such a secret place, the land of tears.” The Little Prince, Antoine de Saint-Exupery

Do animals cry? Probably not. Indian gamekeepers told Charles Darwin stories of elephants that shed tears of sadness, and dog lovers have tales of canine tears, but the emotional tears of humans are unparalleled in the animal kingdom.

We are always making tears

All land dwelling animals, including people, make tears constantly. Eyes are windows on the world, and baseline tears are constant window washers. The window pane is the cornea, a thin panel of collagen, containing very few cells, no blood vessels, and more nerves per square inch than any other part of the body. These nerves signal alarm and summon an army of reflexive tears in response to a speck of dust, a cold wind, or a whiff of an onion. Reflexive tears, which are just a lot of baseline tears, wash out intruders and fill in dry patches on the cornea, keeping it clear and moist to focus light entering the eye. Emotional tears appear in humans during infancy, but not immediately. The crying that infants first do to signal their needs is much like the crying of little chimpanzees – tearless. Emotional tears come later, just like talking. Both are outward expressions of the lives of our minds, and they take a while to learn.

What tears are made of

Tears are much more than little beads of salt water running down your face. They are a three layer sandwich. The oil-containing molecules in the outer layer tighten up the surface of the watery middle layer to keep it from spilling over eyelid and sliding off the surface it protects. The oil floats on the watery middle layer and smooths its surface, optimizing the passage of light through to the eye’s interior. The third part of the sandwich, inside and closest to the eye, is the mucinous layer, kind of a gluey protein that helps tears stick to the eyeball. The mucinous proteins capture and kill biologic intruders like bacteria and viruses, and soak up some of the watery layer to help transfer nutrients, oxygen and moisture to the cornea. Both the oil and mucin slow evaporation of tears as blinking spreads them over the eye.

Evaporation and drainage

Dry spots appear on the cornea after just fifteen non-blinking seconds – easy to do while concentrating or daydreaming. Even with blinking, tears evaporate, or they drain out from the eye into the nose via two tiny lacrimal ducts on the upper and lower eyelids near the nose. If these ducts become scarred or blocked by infection, tears overflow. Six to 10% of babies are born with tear ducts not yet open, but 95% of these will open by age one without any attempt at surgical repair. Conversely, one way of treating dry eyes is to block these ducts with small plastic pellets.

Dry eyes

Too few tears, tears with abnormal composition, and decreased blinking cause dry eyes that itch, sting, burn, get red, and cause blurred vision. Dry eyes are an increasing problem in our air-conditioned, airline-traveling, contact lens-wearing, Lasiked, medicated and aging society. The list of drugs that dry eyes includes many commonly prescribed classes: decongestants, antidepressants, antihypertensives, antihistamines, beta-blockers, hormones, diuretics, ulcer medications, acne drugs, and oral contraceptives. Other causes of dry eyes are infections and immune diseases like rheumatoid arthritis and Sjogren’s syndrome as well as  radiation and radioactive iodine treatment can also damage the tear producing cells. All of these conditions damage the tear producing cells  – the machinery for tear production. 

Remedies for dry eyes 

Treatment of dry eyes is always aimed at removing offending problems and increasing lubrication. The usual tactics include artificial tears, wind protection, air humidification, cessation of unnecessary medications, and treatment of underlying diseases and infections. Excessive tearing often means allergies, or blocked lacrimal ducts leading to poor drainage of baseline tears into the nose.

The tear producing machinery

The medical conditions mentioned above shut down tear production and cause pain and swelling in the lacrimal gland, a spongy little structure tucked up under the upper outer corner of the eyelid. The lacrimal gland is the tear producing factory, aided by the oil-producing Meibomiam glands near the eyelashes, and a cluster of mucin-producing cells in the eyelid lining.

The controls for the machinery

When the lacrimal glands get a call for more tears, either reflexive or emotional, the messages come through the autonomic nervous system, which oversees the automatic functions of the body. Reflexive tears spring from messages sent from the eye and nose. Emotional tears come from messages sent by the limbic system, the deepest and oldest part of the brain, the part that conjures up feelings.

What are emotional tears?

What are emotional tears? Are they just more voluminous baseline tears? Or does emotional crying rid us of “humors of the brain,” as Hippocrates thought? In Roman times, mourners used small glass vials called lachrymators to collect their tears for burial with the one for whom they cried. In today’s laboratory, emotional tears are almost as hard to come by as research money to investigate them. Some dedicated men such as Professor William H. Frey II (Dept. of Pharmaceutics at the U. Of Minnesota) have learned enough to suggest that tears of grief rid the body of some of the products of stress, supporting the claim that crying makes people feel better. Compared to reflexive tears, emotional tears contain up to 25% more proteins, of classes related to stress. Why? No one knows – yet. Emotional tears are still a land of mystery, part of the unique expression of inner life that separates the human animal from the others.