Some degree of watery eyes is normal. Tears are essential for stable vision, to lubricate and nourish the surface of our eyes, to wash away particles and irritants and to protect against infection.

Tears are produced by the lacrimal gland, a tiny gland located under the brow at the outer corner of each eye.

Tears flow over the surface of the eye by the action of the muscles around the eye (the muscle pump) and drain through the puncta (singular punctum), the tiny openings at the inner edge of the eyelids. From here, tears enter tiny channels, the tear canaliculi, and flow through to the lacrimal sac before draining into the nose through the nasolacrimal duct.

Instead of this healthy tear flow, some people experience constantly watery eyes, often made worse by exposure to bright light or cold wind.

Causes of watery eyes

Watery eyes occur because either too many tears are produced or because the tear ducts do not drain properly. Common causes of watery eyes include:

• Overproduction of tears
• Obstruction to tear ducts

Rare causes such as polyps or other nasal conditions that block the nasolacrimal duct or the lacrimal sac.

Overproduction of tears can be due to:

• Dry eyes, with abnormal tear composition and function
• Ingrowing eyelashes, which irritate the eye
• Ectropion or entropion: irritation caused by eyelids turning in or out
• Infections and inflammation: conjunctivitis, blepharitis (inflamed eyelids) keratitis (corneal damage)
• Foreign bodies on the cornea or under the eyelid
• Yawning, laughing, vomiting or eye strain

Tear duct obstruction can be caused by:

• Blockage or narrowing of the opening into the tear canaliculi
• Partial or functional blockage of the tear duct
• Abnormal development of the nasolacrimal duct
• Infection of the lacrimal sac (dacryocystitis)
• Reduced efficiency of the muscle pump related to ageing

Dry eyes causing watery eyes

Ironically, one of the most common causes of excessive tearing is dry eyes or dry eye syndrome. Lack of tears makes the eyes sore. This stimulates a reflex that produces more tears to relieve the uncomfortable feeling. In dry eye syndrome, the efficiency with which tears are able to wet the eyes is not normal and this makes the excessive watering worse.

Ingrowing eyelashes: trichiasis Watery eyes are a common accompaniment to ingrowing lashes. Blepharitis and eyelid infections may result in abnormally positioned eyelashes that constantly scratch the surface of the eye.

Other eye irritation

All surface irritants may be responsible for watery eyes. These include small abrasions, a foreign body under the eyelid, eye drops taken to treat glaucoma or other conditions, environmental irritants, chemicals, smog, airborne allergens or an allergic reaction to mould, dust and dander.

Conjunctivitis

Watery eyes may be associated with inflammation or infection of the conjunctiva, the membrane lining the eyelids. Normal reflex tearing helps to wash away bacteria. Tears also contain enzymes and antibodies that kill bacteria.

Blepharitis

Blepharitis is the inflammation of the rims of eyelids and this causes poorly spreading tears, which result in dry patches on the surface of the eye. The dry patches make the eye feel uncomfortable and this stimulates the tearing reflex.

Improper eyelid position

Watery eyes can also be caused by the position of the lower eyelid, which may be saggy or ‘lax’, turned in (entropian) or turned out (ectropian). Watering associated with thyroid eye disease is also partly caused by abnormal eyelid position.

Stenosis of the opening into the tear canaliculi

This is a common cause of watery eyes and may be as a result of infection or improper eyelid position. Sometimes it can be relieved temporarily by dilating the opening and syringing the tear duct with saline, but often needs a more permanent solution.

Clogged tear duct

A blockage somewhere in the tear canals or nasolacrimal duct can result in watery eyes. In a few cases, blockage may result in acute infection in the tear sac called acute dacryocystitis, which is a bit like an abscess and needs urgent antibiotic treatment and surgical drainage.

Partial or functional blockage of the tear duct

The tear drainage system is open but the tears do not drain away fully because weak eyelid muscles are less effective at pumping the tears into the canaliculi. In addition, the eyelids are usually slack and improperly positioned.

Delayed development of the nasolacrimal duct

This is a common cause of watery eyes in newborn babies. The one-way valves in the nasolacrimal duct are not developed fully at birth and the obstruction causes a backlog of tears. Often the tears accumulate as a sticky discharge.

The blockage usually resolves spontaneously in the first few months of life. Gentle massage over the lacrimal sac can help and cleansing of eyelid secretions prevents secondary infection.

Ageing and watery eyes

Elderly people often have watery eyes due to multiple factors. Ageing can reduce tear production, the eyelids may be slack causing the tear duct opening to become inflamed and the muscle pump around the eye often becomes inefficient and less able to direct tears into the tear canaliculi.