Experiencing tears flowing from just one eye can be unsettling. This seemingly unusual phenomenon has several common explanations related to the eye’s tear production and drainage system.
How Tears Normally Work
Tears are produced by the lacrimal glands, located above each eyeball, and are important for maintaining eye health. These glands supply tear fluid, spread across the eye’s surface with every blink, forming a protective tear film. This film has three layers: an oily outer layer to prevent evaporation, a watery middle layer for hydration and nourishment, and an inner mucus layer that helps the tear film adhere to the eye.
After lubricating the eye, excess tears drain through openings called puncta, located in the inner corners of both the upper and lower eyelids. From the puncta, tears travel through channels called canaliculi into a lacrimal sac, then down the nasolacrimal duct, which empties into the nose. This drainage system explains why your nose might run when you cry. Each eye has its own independent tear production and drainage system, meaning an issue in one eye does not necessarily affect the other.
Common Causes of Unilateral Tearing
Excessive tearing in only one eye results from external irritants or mild internal conditions. A foreign body, such as dust, an eyelash, or grit, can enter one eye, triggering a reflex to produce more tears to flush it out. This heightened tearing is the eye’s natural defense mechanism to clear the irritant.
Environmental factors like wind or smoke can irritate a single eye, leading to increased tear production. Allergies might primarily affect one eye, causing it to water more than the other. An ingrown eyelash, medically known as trichiasis, can continuously rub against the cornea or conjunctiva, causing irritation, redness, and tearing in the affected eye.
Paradoxically, dry eye syndrome can cause excessive tearing, known as reflex tearing. When the eye’s surface becomes too dry or the quality of tears is poor, it triggers the lacrimal glands to produce watery tears. This reflex response can occur in just one eye, leading to a watery, irritated sensation despite underlying dryness.
Understanding Tear Duct Blockage
A frequent cause of one-sided watery eyes is a blocked tear duct, also known as nasolacrimal duct obstruction. This condition occurs when the tear drainage system, which carries tears from the eye to the nose, becomes partially or completely obstructed. When the duct is blocked, tears cannot drain normally and instead back up, overflowing onto the cheek.
Blockages can develop for various reasons. Chronic eye inflammation or infections can lead to scar tissue buildup, narrowing the ducts. Injuries to the face, eye, or nose may cause swelling or tissue changes that impede tear flow. Age-related narrowing of the puncta, the drainage holes, or the ducts themselves can contribute to obstruction. A tumor near the tear drainage system can also cause a blockage, and this backup of tears can increase the risk of infection within the tear duct system.
When to Seek Medical Advice
While many instances of watery eyes resolve on their own, certain symptoms warrant medical attention. You should seek medical attention if the excessive tearing is persistent and does not improve. A doctor should evaluate any accompanying symptoms such as vision changes, including blurred vision.
Other concerning signs include pain around the eye, redness, swelling, or discharge, which might be yellow, green, or bloody. If you feel something is stuck in your eye, or if tearing is accompanied by a severe headache or tenderness around your nose or sinuses, prompt medical evaluation is needed. These symptoms could indicate a more serious underlying condition that requires professional diagnosis and treatment.