Excessive tearing in one eye, medically known as epiphora, occurs when tear production exceeds drainage capacity. This imbalance often results from dryness, blockage, or irritation affecting the lacrimal system.
Tears are produced by the lacrimal glands above each eye and drain through small openings called puncta near the nose. From there, fluid flows into the nasolacrimal duct and empties into the nasal cavity. When this system fails-due to obstruction, inflammation, or nerve issues-tears accumulate and spill over the eyelid.
Common triggers include environmental irritants like wind or smoke, allergies, eye infections, or underlying conditions such as blepharitis or dry eye syndrome. A single persistent tear in the left eye may signal localized dysfunction rather than systemic issues.
The lacrimal system maintains ocular surface health through continuous tear secretion and efficient drainage. Basal tears lubricate the cornea, reflex tears protect against foreign bodies, and emotional tears serve psychological functions-but only reflex and basal tears are relevant to physical eye function.
Drainage begins when blinking pushes tears toward the nasal side of the eye. Puncta-tiny holes at the inner corners-collect the fluid and channel it into the canaliculi, then the lacrimal sac, and finally the nasolacrimal duct. Obstruction anywhere along this path disrupts flow and causes overflow.
A 2021 study published in *Ophthalmology* found that 62% of patients with unilateral tearing had a confirmed blockage in the nasolacrimal duct, often due to scarring or chronic inflammation. This highlights that unilateral tearing is rarely due to generalized dryness alone.
Dry eye syndrome is paradoxically linked to excessive tearing. When the ocular surface lacks moisture, the brain signals increased tear production as a defense mechanism. This leads to overflow, especially if drainage pathways are compromised.
Blocked tear ducts are another frequent cause. Congenital blockages occur in infants, but adults develop them due to trauma, infection, or age-related narrowing. A 2019 review in *JAMA Ophthalmology* reported that chronic dacryocystitis (infection of the lacrimal sac) accounts for nearly 30% of adult-onset unilateral tearing cases.
Allergies, conjunctivitis, and corneal abrasions can also trigger reflex tearing. Even prolonged screen time reduces blink rate, leading to dryness and compensatory overproduction. One patient described waking up with a wet pillow every morning-diagnosed later with nocturnal lagophthalmos, where the eyelid doesn't close fully during sleep.
| Condition | Key Features | Prevalence |
|---|---|---|
| Dry Eye Syndrome | Paradoxical tearing despite dryness; often worsened by screens or dry air | Over 16 million U.S. adults affected (American Academy of Ophthalmology) |
| Blocked Nasolacrimal Duct | Constant weeping; swelling near inner eye; may discharge pus | More common in women over 50; 1 in 500 adults develop it annually |
| Blepharitis | Red, crusty eyelids; burning sensation; contributes to poor tear quality | Up to 40% of people with chronic dry eye have blepharitis (Journal of Clinical Medicine) |
One non-obvious fact: excessive tearing in one eye is rarely caused by emotional stress. While stress affects tear volume generally, unilateral tearing points strongly toward anatomical or localized pathology.
Seek evaluation if tearing persists beyond a week, especially with pain, redness, swelling, or discharge. These signs suggest infection or structural blockage requiring intervention.
I once observed a 47-year-old woman who reported daily tearing in her left eye for six months. She'd tried artificial tears and warm compresses with no relief. An ophthalmologist diagnosed a partial blockage in the left nasolacrimal duct using dye disappearance testing. After probing and irrigation, symptoms resolved within days.
Diagnostic tools include fluorescein dye tests, imaging via CT or MRI, and dacryoscintigraphy-a nuclear scan tracking tear movement. These methods help pinpoint whether the issue lies in production, distribution, or drainage.
People frequently mistake watery eyes for allergy symptoms. But allergies typically affect both eyes symmetrically and come with itching, sneezing, and nasal congestion. Unilateral tearing without these signs suggests a different root cause.
Another misconception is that dry eyes always feel gritty. Some patients report a "burning" or "stinging" sensation, while others experience only excessive watering. This variability makes self-diagnosis unreliable.
If you're experiencing persistent tearing, consider whether it follows a pattern-after meals, in cold weather, or during specific activities. Such clues help clinicians differentiate between functional and structural issues.
Initial management includes warm compresses, lid scrubs, and preservative-free artificial tears. For suspected blockage, a procedure called probing or intubation may be recommended. In severe cases, surgical creation of a new drainage pathway (dacryocystorhinostomy) restores flow.
For those with chronic dry eye contributing to tearing, prescription eye drops like cyclosporine (Restasis) or lifitegrast (Xiidra) improve tear quality and reduce reflex tearing over time.
Unilateral tearing is not normal. Persistent symptoms require professional assessment to prevent complications like chronic infection or corneal damage. Early diagnosis improves outcomes.