Unilateral tearing, where tears emerge from only one eye, can be puzzling. While both eyes typically work in tandem, various factors can lead to this phenomenon.
The Science of Tears
Tears are fluids produced by the lacrimal glands, located above the outer corner of each eye. These glands continuously secrete basal tears, forming a protective film over the eye’s surface. This film keeps the eye lubricated, nourished, and free from debris, consisting of three layers: an oily outer layer, a watery middle layer, and a mucin inner layer.
Beyond basal tears, the eyes produce reflex tears and emotional tears. Reflex tears respond to irritation, flushing out harmful substances like dust or smoke. Emotional tears are triggered by strong feelings. After serving their purpose, tears normally drain through small openings called puncta, located in the inner corner of the eyelids, into tear ducts that lead to the nasal cavity.
Why Only One Eye Cries
Unilateral tearing, or epiphora, often results from an issue affecting one eye’s tear production or drainage. A common reason is an irritant like dust or an eyelash. When a foreign body enters one eye, it triggers reflex tearing to flush it out, causing tears from only that side.
Allergies can cause unilateral tearing if one eye is more reactive. Allergic reactions inflame the eye, increasing tear production. Environmental factors like wind or cold can also provoke a reflex tearing response in one eye.
A blocked tear duct, or nasolacrimal duct obstruction, is a frequent cause of chronic unilateral tearing. Tears cannot drain properly, accumulating and overflowing onto the cheek. This blockage can lead to watery eyes, discharge, and recurrent eye infections.
Dry eye syndrome can also lead to excessive tearing in one or both eyes. When the eye’s surface is too dry, it becomes irritated, triggering a reflex to produce tears. These reflex tears often lack the proper balance for effective lubrication, leading to a cycle of dryness and watery eyes.
Eye infections like conjunctivitis (pink eye) can cause unilateral tearing, redness, itching, and discharge. These infections inflame the eye, increasing tear production to clear the infection. A corneal abrasion or injury to the eye’s outer layer can also cause pain and reflex tearing.
In rare instances, neurological conditions can impact tear production or drainage, leading to unilateral tearing. Tumors or cysts near the lacrimal gland or tear drainage system are also rare but possible causes.
When to Consult a Doctor
While many instances of unilateral tearing are temporary, certain symptoms warrant professional medical attention. Consult a doctor if tearing is persistent, causes pain, or is accompanied by vision changes. Other concerning signs include significant redness, discharge, eyelid crusting, or a feeling that something is constantly in the eye. If a foreign body cannot be easily removed or if there is suspicion of an eye injury, prompt medical evaluation is important.