Bacterial conjunctivitis starting in one eye
Bacterial conjunctivitis commonly begins in one eye and then spreads to the other, often within a day or two. In the early stage, when only one eye is affected, people often assume something more specific is wrong, but this is simply the natural history of bacterial conjunctivitis: the infection arrives in one eye first and then spreads through hand-to-eye contact or by sharing towels and pillowcases.
The discharge in bacterial conjunctivitis is typically yellow or green and tends to accumulate overnight, sticking the eyelids together on waking. The eye is usually red and uncomfortable but not painful in a deep, aching sense. Vision is not usually reduced. The condition is self-limiting in most healthy adults, clearing within seven to ten days without antibiotic drops, though topical antibiotics are commonly prescribed to shorten the duration and reduce the risk of spread.
If the discharge from one eye is unusually heavy, or if it is accompanied by reduced vision, significant pain, or intense light sensitivity, this warrants same-day assessment rather than waiting for the condition to resolve on its own.
Dacryocystitis: infection of the tear sac
The tear drainage system runs from the inner corner of each eye, through a small sac called the lacrimal sac, and down through a channel in the bone into the nose. When this drainage pathway becomes blocked, stagnant tear fluid and mucus can accumulate in the lacrimal sac, creating a warm, moist environment that bacteria can colonise. The resulting infection is called dacryocystitis.
Dacryocystitis is almost always one-sided. It produces a characteristic and recognisable picture: redness, swelling, and tenderness at the inner corner of the eye, just below the medial end of the lower eyelid. There is often discharge at the inner corner, and in some cases pressing gently over the swelling produces a reflux of mucus or pus through the tear duct puncta (the tiny openings at the inner corners of the eyelids).
Acute dacryocystitis requires antibiotic treatment, which is usually given orally. A significant or rapidly enlarging swelling, or one accompanied by high fever or spreading redness, may require hospital admission for intravenous antibiotics. Once the acute infection has settled, the underlying blocked tear duct usually needs to be addressed surgically to prevent recurrence.
- A tender, swollen lump at the inner corner of one eye
- Redness and warmth spreading beyond the inner corner toward the cheek
- Fever alongside the eye swelling and discharge
- A rapidly enlarging or fluctuant swelling that looks as though it may burst
Blocked tear duct without active infection
A blocked nasolacrimal duct, even without superimposed infection, can cause a chronic one-sided discharge. When tear drainage is obstructed, tears and mucus accumulate and may overflow at the inner corner of the eye. The discharge in uncomplicated blocked tear duct is typically clear or white and mucoid rather than yellow or green, and it may be associated with a watery eye on that side.
Pressing gently over the tear sac area in a patient with a blocked duct often produces a reflux of clear mucus through the puncta, which is diagnostically useful. This finding indicates that the sac is filled with stagnant fluid and that drainage is obstructed downstream.
A blocked tear duct on its own does not require urgent treatment, but it is worth having assessed by an ophthalmologist if the discharge is troublesome, as surgical unblocking (dacryocystorhinostomy) is a reliable and effective procedure.
Watery eye alongside dischargeA one-sided watery eye and one-sided discharge occurring together strongly suggest a blocked tear drainage pathway on that side. The two symptoms share a common cause: the tear drainage system is not working on that side.
Corneal infection (keratitis)
An infection of the cornea, the clear front surface of the eye, can produce discharge alongside other symptoms that are typically more prominent and alarming than in conjunctivitis. Corneal infection causes significant pain, often described as a deep, aching, or severe discomfort, marked light sensitivity, reduced vision if the infection is near the centre of the cornea, and a visible white or grey opacity on the corneal surface.
Contact lens wearers are at elevated risk of corneal infection, particularly if they sleep in their lenses or use them beyond the recommended wear period. Acanthamoeba keratitis, a particularly serious corneal infection caused by a microscopic organism found in tap water and swimming pools, is almost exclusively a disease of contact lens wearers who have been exposed to contaminated water.
Any red, painful eye with reduced vision in a contact lens wearer should be treated as a potential corneal infection until proven otherwise, and assessed urgently the same day.
Foreign body
A foreign body on or in the eye, such as a fragment of metal, grit, or plant material lodged under the eyelid or on the corneal surface, produces a one-sided reflex tearing response and, if the eye is irritated enough, a mucopurulent discharge. The hallmark symptom is a sensation that something is in the eye that does not go away with blinking or washing.
A foreign body embedded in the cornea or under the upper eyelid requires removal by an ophthalmologist. Attempting to remove it at home risks pushing it deeper or causing additional corneal damage. If you have persistent foreign body sensation in one eye that has not resolved after gentle irrigation, seek assessment the same day.
One-sided discharge and reduced vision
The combination of discharge from one eye and reduced vision in that eye is always worth taking seriously. Bilateral conjunctivitis rarely causes significant visual loss, but a corneal infection, a serious dacryocystitis, or certain other conditions affecting one eye can do so. If discharge is accompanied by any of the following, seek same-day assessment.
Seek same-day assessment if
- The discharge is accompanied by pain in or around the eye
- Vision is reduced in the discharging eye
- There is significant light sensitivity alongside the discharge
- The eye is very red with a visible opacity or white spot on the cornea
- There is swelling at the inner corner of the eye with fever or rapidly spreading redness
- You are a contact lens wearer and the eye is red and uncomfortable
Common questions
My eye has been sticky every morning for weeks. Should I be concerned?
Chronic morning stickiness in one eye, where the eye is pasted shut or has a buildup of mucus each morning, suggests either a drainage problem (blocked tear duct or dacryocystitis) or chronic low-grade blepharitis. It is not usually urgent but is worth having assessed if it is persistent and troublesome.
Can a watery eye from a blocked tear duct look like discharge?
Yes. A chronically watery eye with a blocked tear duct often produces a mucopurulent overflow at the inner corner, which people describe as discharge. The tears and mucus accumulate because they cannot drain, and they pool at the corner of the eye where they are visible as a sticky residue, particularly on waking.
Is yellow discharge always bacterial?
Yellow or green discharge strongly suggests bacterial infection, but it is not exclusively so. Viral conjunctivitis can produce some mucopurulent discharge, though typically less than bacterial conjunctivitis. The character of the discharge alone cannot reliably distinguish the two, but the clinical setting, spread pattern, and associated symptoms help to narrow the diagnosis.
