Nocturnal epiphora, the medical term for watering eyes during sleep, is a common symptom. Individuals often wake with tears pooled on their cheeks or crusting on their eyelids. This overflow occurs due to an imbalance in the system that controls tear production and drainage. The cause is usually related to either the eye producing too many tears in response to irritation, or the normal drainage system failing to keep up.
Why the Eye Produces Too Many Tears
The most frequent cause of overnight watering is reflex tearing, where the eye responds to dryness by flooding the surface with tears. During the night, the eyes can become dry due to incomplete eyelid closure, a condition called nocturnal lagophthalmos, which exposes the cornea to the air. This exposure causes rapid evaporation of the tear film, irritating the delicate eye surface.
When the corneal nerves detect this dryness, they send a distress signal to the main lacrimal gland, which then secretes a large volume of tears. These reflex tears are typically more watery than normal basal tears and lack the necessary oil and mucus components to properly coat and lubricate the eye. Since they evaporate quickly and are of poor quality, they fail to resolve the underlying dryness, creating a cycle of irritation and temporary flooding.
A related issue is Meibomian Gland Dysfunction (MGD). MGD occurs when the tiny glands along the eyelid margin fail to produce the oily layer of the tear film. This lipid layer is responsible for preventing the watery layer from evaporating too quickly. Without a stable oil layer, the tear film breaks up rapidly, causing the eye to dry out and trigger the reflex tearing mechanism.
How Poor Drainage Causes Overflow
The tear drainage system, or lacrimal apparatus, is designed to channel tears away from the eye surface and into the nasal cavity. Tears normally flow through two small openings, called puncta, located on the inner corner of the upper and lower eyelids. From there, they travel through the canaliculi and into the nasolacrimal duct, eventually draining into the back of the nose and throat.
When you are lying down, the gravitational assistance that helps pull tears toward the puncta is significantly reduced, which slows the passive drainage. Any pre-existing narrowing of the puncta (punctal stenosis) or a partial blockage within the nasolacrimal duct becomes a more pronounced problem in this horizontal position. Tears pool on the eye surface because the system cannot handle the normal tear volume without gravity’s help.
Eyelid position can also impair this drainage process, particularly with age-related changes. If the lower eyelid sags or rolls outward (ectropion), the punctum is pulled away from the eye surface, preventing effective tear collection. Conversely, if the eyelid rolls inward (entropion), the lashes can irritate the eye, stimulating tear production while the punctum is poorly positioned to drain them.
Overnight Environmental Triggers
External elements in the sleeping environment can irritate the eyes or accelerate tear evaporation, triggering reflex tearing. Low humidity is a major factor, especially in bedrooms where heating systems or air conditioning units are running, drying out the air significantly. When dry air passes over the exposed corneal surface, moisture evaporates more quickly, leading to irritation and subsequent tear overproduction.
The direct flow of air from a vent, ceiling fan, or open window across the face can also exacerbate the problem by speeding up tear film evaporation. Furthermore, the bedroom environment is a natural collector of microscopic allergens like dust mites, pet dander, and mold spores. Exposure to these irritants overnight can cause localized allergic conjunctivitis, resulting in inflammation that directly stimulates tear production.
Even certain sleeping positions can contribute by placing physical pressure on the eye or the drainage system. Sleeping with the face pressed into a pillow may cause the eyelid to slightly open or compress the lacrimal sac, which is part of the drainage pathway. This compression can temporarily impede tear flow, causing the tears to overflow onto the face.
When To Talk To An Eye Doctor
While occasional watery eyes upon waking may be benign, persistent or worsening nocturnal tearing warrants a professional examination. Seek an assessment if the tearing is accompanied by pain, a noticeable change in vision, or significant redness. These symptoms may suggest an underlying infection, inflammation, or corneal issue requiring targeted treatment.
It is important to see a specialist if the tearing occurs only in one eye, which often signals a structural issue like a blocked tear duct or punctal obstruction. The doctor can perform specialized tests, such as a fluorescein dye disappearance test, to check the efficiency of your tear drainage system. Treatment may range from lubricating eye ointments applied at night to procedures designed to open a narrowed drainage pathway.