The common problem of watery eyes has many causes which are most easily understood if we approach it like a plumbing issue.
Tears are produced in glands (lacrimal glands) located in the outer corners of the upper eyelids, just underneath the bone above our eyes. The tears flow out of the gland through ducts in the eyelids and then wash over the surface of the eyes before entering a small channel (the canaliculus) through a minute opening called the punctum. They then flow down into the lacrimal sac, finally draining into the nose via the tear
Excessive tearing may be secondary to an overproduction from the gland (akin to too much water coming from the faucet) or insufficient drainage (akin to obstruction in the pipes). However, overproduction is usually a reaction to other inciting factors such as dry eyes or ocular allergies. When the eyes are dry and the surface becomes irritated, the body compensates by producing extra tears to lubricate the ocular surface. This is a protective function to ensure the eyes are bathed in nutrient-rich fluid and to reduce the risk of surface damage to the eye.
Seasonal allergies cause tearing when the body attempts to cleanse the eye of irritating allergens. These same allergens trigger a histamine-induced response that also increases tear production. No matter the cause of overproduction, the volume of tears may overwhelm the body’s baseline drainage capacity, resulting in tears that run down your cheeks (akin to the sink overflowing).
In cases of overproduction, tearing is often alleviated when the underlying condition is addressed. With dry eyes, many patients find relief with over-the-counter artificial tear drops. The only caution here is to avoid formulations made for “red eyes” as these often have an additional ingredient that may lead to worsened redness of the eyes with long-term use. If tears are applied more than 3-4 times per day, it is also advisable to use a preservative-free version to lessen the potential for irritation (and hence recurrent tearing). In the case of allergies, many patients find relief with over-the-counter or prescription allergy eye drops or oral allergy medications.
Poor drainage of tears is another cause of excessive tearing. Just as with partially or fully blocked pipes under the sink, any abnormalities to the lacrimal apparatus result in reduced or absent outflow of the tears.
Sometimes the opening of the tear drainage system (the punctum) is narrowed. This prevents the tears from entering the system, similar to having a drain hole in the sink that is too small, or even absent. In these cases, patients may get relief with an office procedure to “stretch” the opening wider. However, if the opening is too narrow to attempt stretching, or the stretching does not last, surgical options are the next steps. In some cases, the opening is stretched, and a tube is left in the drainage system for a few months to keep things open and help the body adapt and maintain a wider punctum. This would be like stretching the drain hole in the sink and then leaving a snake in the area for a few months to keep it open. When the tube is removed, the opening should remain more widely open.
Another cause of poor outflow is poor alignment of the eyelids with the eyes. If the lids are loose or not in proper contact with the eye, the opening to the drainage system will not be immediately adjacent to the surface of the eye. Thus, the tears will not drain down their natural path from the surface of the eye down into the pipes just past the opening (the canaliculi). In these cases, the eyelid position will need to be restored surgically.
There is a pipe (canaliculus) which lies just past the opening of the drainage system (the punctum). The pipes may be scarred from prior trauma or, as often the case, previously placed punctal plugs. To treat dry eyes, plugs are placed into the punctum or the far end of the canaliculus just beyond the punctum. In either location, this would be like placing a plug in the drain hole of the sink. The rationale is to prevent the tears from exiting the eye and thus remaining on the ocular surface, allowing for lubrication. In the case of a punctal plug, this can easily be removed to allow the tears to drain past. Plugs placed into the canaliculus are more difficult to address. Removal often requires a surgical approach as there is no “handle” to grasp in order to remove it from the lacrimal “pipes.”
Lastly, the lacrimal sac and duct may be the source of tearing. Sometimes small stones develop in the tear sac and create intermittent blockages of the opening where the sac meets the next outflow pipe, the nasolacrimal duct. Once lodged, stones prevent tears from draining into the nose. As the tear level builds up in the sac, the small stone may “float” out of the tight area, allowing tears to drain down into the duct from the sac. Patients describe episodes of terrible tearing that flare when the stone is lodged, or “stuck.” As time goes on, the stone becomes larger and may permanently obstruct
If the nasolacrimal duct becomes narrowed or totally occluded, tears become stagnant in the lacrimal sac. This would be like the pipe under the sink becoming narrowed or blocked. Thus, the tears (water) do not exit the system and subsequently pool in the sac (sink). Once sufficiently full, the tears (water) spill onto the surface of the eye (over the edge of the sink). If a duct is narrowed, it may be widened. A surgical procedure is done to place a stent (tube) through the entire lacrimal system. It is left in place for a few months in the hopes that upon removal, the narrowed area remains more open.
In cases where the duct is totally obstructed or a stent cannot be placed, the blocked duct must be bypassed. A DCR surgery (dacryocystorhinostomy) creates a new outflow track from the lacrimal sac (akin to adding a new pipe under the sink to bypass the blocked one). Once the new track is created, a stent is left in place for a few months to ensure the new path does not scar closed.
The mechanism for tear production and outflow is a finely tuned system. Any anomaly of the harmonious mechanism may lead to bothersome watery eyes and blurry vision. The analogy to the plumbing of your sink helps to explain the cause of the tearing and allows for more appropriate treatment of the cause.
Dr. Hui is the founder of The Eyelid Institute in Palm Desert. She is an oculoplastic surgeon with a special interest in helping patients with eyelid, lacrimal and orbital conditions and can be reached at (760) 610.2677.