When tears flow from only one eye, a condition known as unilateral epiphora, it means the delicate balance of tear production and drainage has been disrupted on one side of the face. While the symptom may cause immediate concern, the underlying cause is often a temporary physical issue localized to that eye or its drainage system.
Understanding the Lacrimal System
The lacrimal system manages the continuous cycle of tear creation and removal, operating as two distinct systems, one for each eye. Tears are primarily produced by the lacrimal gland, located in the upper outer portion of the eye socket. This gland secretes the aqueous component of the tear film that spreads across the eye’s surface, lubricating the cornea and flushing away debris.
After washing the eye, tears are collected at the inner corner of the eyelid, near the nose. They enter tiny openings called the puncta, which lead through small tubes called canaliculi into the lacrimal sac, a reservoir behind the bridge of the nose.
The final step is the nasolacrimal duct, which carries the fluid from the lacrimal sac down into the nasal cavity. Tears typically evaporate or are swallowed once they reach the nose, explaining why crying often causes a runny nose.
Common Reasons for Unilateral Tear Overflow
The most frequent causes of one-sided tear overflow generally involve a temporary excess of tear production or a mild, localized obstruction in the drainage pathway. Unilateral symptoms usually point to an issue affecting the eye itself or the corresponding drainage structures.
Reflex Tearing
Reflex tearing is the body’s protective response to localized irritation, causing the lacrimal gland to immediately produce a large volume of tears to wash the irritant away. This overproduction can be triggered by a single eyelash rubbing the surface of the eye, a small piece of dust, or a microscopic corneal abrasion. Since the irritation is isolated to one eye, the resulting overflow is also limited to that side.
Environmental factors frequently induce this reflex tearing, such as exposure to strong wind, smoke, or airborne chemicals. These irritants stimulate the nerve endings on the eye’s surface, signaling the lacrimal gland to initiate a flushing response.
Drainage Obstruction and Dry Eye
Mild allergic reactions or temporary inflammation, like that caused by a common cold, can cause the lining of the nasolacrimal duct to swell slightly. This slight swelling can temporarily narrow the duct, slowing the drainage of tears and causing them to back up and spill over the lower eyelid.
A paradoxical condition known as reflex hypersecretion, or the “dry eye paradox,” can cause excessive tearing. When the eye surface becomes dry, the body attempts to compensate by intensely stimulating the lacrimal gland to produce a sudden flood of tears. Because this dryness or irritation can sometimes be more pronounced in one eye than the other, the resulting compensatory tearing may also be unilateral. These causes are often transient, resolving naturally once the irritant is removed or the temporary swelling subsides.
Indicators That Require Medical Attention
While many cases of unilateral tearing are temporary, certain accompanying signs suggest a more complex issue requiring professional diagnosis. Any tearing that persists for several weeks without an obvious, temporary cause should be evaluated by an eye care specialist. Chronic overflow can indicate a structural obstruction that will not resolve on its own.
The presence of pain is a warning sign, particularly if it is localized to the eye, the orbit, or the area around the lacrimal sac near the nose. This pain, especially when accompanied by tenderness or swelling, may indicate a developing infection within the tear drainage system.
Other changes to the appearance or function of the eye also warrant a prompt consultation:
- Noticeable redness of the eye.
- A significant change in vision, such as blurring or loss of clarity.
- The presence of thick discharge.
- Discharge that appears yellow or green, signaling a bacterial infection.
A history of trauma to the face or nasal area, or a recent sinus infection, should also raise the need for a professional check-up if it precedes the onset of unilateral tearing. These events can sometimes lead to damage or blockage of the tear drainage pathway.