Epiphora may have many causes. It may be a result of either excess secretion or diminished tear drainage.
In infants, the condition typically is the result of blockage of tear drainage in underdeveloped tear ducts that aren’t yet fully opened. When tear ducts are blocked, tears accumulate and spill over. Tear ducts don’t produce tears, but rather provide drainage for the eyes through small openings in the lid near the nose, called puncta.
A significant portion of children outgrow their tear drainage obstruction. Others may require a simple probing to open the drainage of tears into the nose, which is the normal way tears leave the eye.
In adults, blockages can cause epiphora as a result of infection or deposition of material blocking the drainage mechanism. Certain medications can also cause epiphora. Epinephrine, some types of eye drops, and chemotherapy drugs, for example, can all cause excessive tear production by altering one or more of the tear constituents.
Assuming the patient has not sustained an injury or has a foreign body, occasionally overproduction of tears is the culprit, which may surprisingly be a symptom of dry eye because the quality of the tears is insufficient to do its job. The reflex mechanism in the brain says “produce more tears.”
Sagging of the lids with aging can cause both diminished tear production and elimination. This may lead to infection, and if the eyes do not close fully during sleep, this can cause dry eye. Sometimes a spouse or significant other can check for eyelid closure when their partner is asleep. This has frequently uncovered previously unknown exposure of the cornea.
Tears aren’t a single component, but rather contain three layers that form a film over the eye with each blink. The outer layer is oil-based, followed by the aqueous layer — the watery component that gives tears their distinct salty taste. The mucin layer interacts directly with the surface of the cornea. If each of these layers is in balance, the tear distribution and function is normal and vision is optimal.
Non-evaporative dry eye usually occurs when the aqueous layer is either inadequate, inflamed, or has excessive salt content. Non-evaporative dry eye is caused by decreased or inadequate lipid production from the lid Meibomian glands, which if inadequate causes premature evaporation of tears. Anyone familiar with the drying effects of salt water will immediately understand how tears can be both be a wetting agent and irritating.
The oil-based component of the tears is derived from secretions of the meibomian glands in the lids. In order to produce
lid oil secretion, there needs to be an adequate closure of the lids between blinks. We can video lid closure and frequency
using a high-resolution video technology which analyses the extent of lid closure, frequency, and intensity of lid closure as well as the size of the "tear lake" formed where the lower lid touches the cornea
Commonly, if you have dry eye, you may complain of watery eyes and that your eyes feel itchy or irritated. This is often attributed to irritants in the air, such as smog, smoke, or allergens, but may, in fact, be an abnormality of the ocular surface.
Aqueous tears are produced by the lacrimal glands. They are not visible but are located above the eye laterally. The seventh cranial nerve stimulates the lacrimal gland to secrete tears. The term crocodile tears have a real basis.
The nerve that controls saliva secretion and the nerve that stimulates tear secretion travel together through a short canal in the skull. In certain conditions both nerves can be damaged, usually after a stroke or some form of inflammation. In the healing process, something called aberrant regeneration occurs and seeing food can cause the eyes to tear. It is a not uncommon finding in Bell’s Palsy.
Lipid tears are oily and come from lid secretions. Inflammation, infection and “plugging” (inspissation) of the lid glands cause what is called evaporative dry eye, because the oil layer prevents evaporation of the aqueous tears. Evaporative and non evaporative (decreased aqueous tear production) frequently coexist. Studies have shown the coexistence of both types of dry eye occurs in almost 35% of dry eye patients.
The mucin layer of tears is infrequently discussed primarily because there doesn’t exist good ways to diagnose and treat mucin deficiency. Mucin is produced by cells called the crypts of Henle. These cells exist on the surface of the eye, and when damaged can prevent the tears from binding to the surface of the cornea. This doesn’t allow the tears to flow evenly over the cornea, leaving dry spots which are both painful and an invitation to infection.
Persistent tearing should not be taken lightly. Even if dry eye is not the culprit, a low grade infection or a very small foreign body (usually metallic from working on a car or motorcycle without protective eyewear) may become embedded in the cornea.
I once had a patient who complained of excessive tearing. She told me several months ago she had cleaned out a high shelf in her closet. On close inspection, I found a small seedling growing in the cul de sac, the space between the lids and the eye. Another reason to wear protective eyewear!
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