A tearing eye can be simultaneously a simple and very complicated problem. The fundamental causes of tearing are simple to understand, but sorting them out and effecting a solution can be quite complicated and difficult.
The eye must be constantly lubricated. At low levels of drying, the eye may be mildly uncomfortable. In cases of severe dryness, the eye may be extremely painful, and vision may be permanently lost. A healthy eye is one in which the rate of tear production equals the rate of tear outflow through the tear drain, plus the rate of tear evaporation off the eye.
In brief, normal, healthy tears are composed of an admixture of three layers of oil, aqueous, and mucin, produced by multiple glands. The largest tear-producing gland is the lacrimal gland, which lives in the upper-outer portion of the eye socket, just above the eye. Tears constantly wash over the eye, propelled by a normal blink, and then are actively suction-pumped down the tear drain system into the nose and back of the nasal pharynx where they are swallowed.
Excessive tearing may be grouped into one of the following categories:
I. DECREASED TEAR OUTFLOW
Normal tear production but diminished tear outflow may lead to tears backing up in the eye and pouring down the face. The obstruction may be at the level of a) the puncta (the opening to the canaliculi), b) canaliculus (tube bringing tears to the lacrimal sac), c) lacrimal sac, d) nasolacrimal duct. An obstruction of the nasolacrimal duct (NLDO) is the most common location seen in adults, while a non-patent valve at the far end of the nasolacrimal duct (Valve of Hasner) is the most common location in infants. Different procedures are performed for obstructions at these different locations: a) punctoplasty, b) canaliculoplasty or conjunctivodacryocystorhinostomy (cDCR) or c) dacryocystorhinostomy (DCR) or e) probing and intubation with stents.
Since the tears are normally actively moved across the eye and pumped down the tear drain by natural eyelid blinking, a weakness of the 7th cranial nerve (Facial nerve) or interruption of eyelid blinking may also lead to a form of decreased tear outflow.
II. INCOMPETENT CONTAINER
If the eyelids, especially the lower eyelid, is too loose or turned outward (ectropion), tears can’t be held effectively in the pocket between the lower eyelid and the eye (the inferior sulcus) and thus pour down the face.
III. TEAR OVER PRODUCTION
The most common cause of tear overproduction is a dry eye! The eye is not terribly smart. When it feels an irritation, it suspects a foreign body, such as a twig or particle of dirt, and produces large amounts of fluid to wash the irritant away. The problem is that this is not a good quality tear with all the essential healthy lubricating components, but a fluid that is mostly saltwater. Often, the rate of washing fluid production greatly exceeds the eye’s normal tear drain ability, and “tears” pour down the face. There are, of course, many causes of eye irritation, including blepharitis or an eyelid (entropion) or eyelash (trichiasis) turned inward and rubbing on the eye.
IV. OILY TEAR FILM
People often complain of “tearing” when what they really mean is their vision is “smeared” or “swimmy” as though they are underwater. This is frequently caused by a thick oil slick in the tear film, which is the result of posterior lid margin disease, called blepharitis or meibomitis.