Corneal Ulcers and Serious Eye Infections: Signs and Urgency

Most eye infections are mild. Viral and bacterial conjunctivitis, the familiar pink eye, are uncomfortable but usually settle without lasting harm. Infections that reach the cornea (the clear window at the front of the eye), the inside of the eye or the tissues of the eye socket are a different matter: they can damage vision permanently within days, sometimes within hours. Recognising the difference is one of the most useful pieces of eye knowledge anyone can have.

This guide explains infectious keratitis and corneal ulcers, including bacterial, fungal, Acanthamoeba and herpes simplex infections; the special risks for contact lens wearers; endophthalmitis, an infection inside the eye; and orbital cellulitis, an infection of the eye socket. Above all, it explains why these conditions are emergencies and what to do if you suspect one.

Infection versus inflammation: why location matters

The eye has several layers, and the danger of an infection depends on where it is. The conjunctiva is the thin membrane over the white of the eye and inside the lids; infection here usually causes redness, discharge and grittiness but little pain and normal vision. The cornea is clear and has no blood vessels, so it relies on tears and a healthy surface for defence. Once microbes break through its outer layer, they can multiply quickly, and the scar that remains can permanently blur vision. Deeper still, the inside of the eye contains fluid and the delicate retina, which tolerate infection very poorly.

Our guides to conjunctivitis and red eye causes cover milder conditions in more detail.

Infectious keratitis and corneal ulcers

Keratitis means inflammation of the cornea. When an infection destroys part of the corneal surface and underlying tissue, it is called a corneal ulcer. Infectious keratitis is a leading cause of preventable visual impairment worldwide, especially in agricultural regions where eye injuries with plant material are common.

Bacterial keratitis

Bacteria are the most common cause of corneal ulcers in many high-income countries. Pseudomonas aeruginosa, a bacterium that thrives in water and contact lens cases, is particularly feared because it can destroy corneal tissue within a day or two. Staphylococci and streptococci are also common.

• Risk factors: contact lens wear (especially overnight), corneal injury, dry eye, previous eye surgery, eyelid problems, and long-term use of steroid drops.
• Symptoms: rapidly increasing pain, redness, light sensitivity, blurred vision, watering or discharge, and a visible white spot on the cornea.
• Treatment: the doctor takes samples (corneal scrapings) for laboratory testing, then starts intensive antibiotic eye drops, initially as often as every hour, day and night. Treatment is adjusted according to results and response.

Fungal keratitis

Fungal infections are more common in warm, humid climates and after injuries with plant matter, such as a twig or crop leaf scratching the eye. They also occur in contact lens wearers and in people using steroid drops. Fungal ulcers often develop more slowly than bacterial ones, may have feathery edges, and can penetrate deep into the cornea. Treatment requires antifungal drops for weeks to months and sometimes tablets or surgery. The Mycotic Ulcer Treatment Trial (MUTT) helped establish natamycin as a preferred topical treatment for filamentous fungal ulcers.

Acanthamoeba keratitis

Acanthamoeba is a microscopic organism found in tap water, swimming pools, hot tubs, lakes and soil. It is a rare cause of keratitis but one of the most difficult to treat, and the great majority of cases occur in contact lens wearers. Typical risk behaviours include rinsing lenses or cases with tap water, swimming or showering in lenses and using homemade saline.

• Symptoms: pain that can be severe and out of proportion to what the doctor sees, light sensitivity, redness and blurred vision. Early stages are easily mistaken for herpes or a simple abrasion.
• Diagnosis: special laboratory tests, PCR or confocal microscopy.
• Treatment: specific antiseptic drops used intensively for many months. Some patients need corneal transplantation once the infection is controlled.

Herpes simplex keratitis

Herpes simplex virus type 1, the same virus that causes cold sores, can infect the cornea. After the first infection, the virus stays dormant in nerves and can reactivate, so herpes keratitis tends to recur, often in the same eye. Each episode can leave more scarring and reduce corneal sensation.

• Forms: epithelial keratitis, affecting the surface with a characteristic branching (dendritic) ulcer, and stromal keratitis, a deeper immune reaction that causes haze and scarring.
• Symptoms: red, watery, light-sensitive eye with blurred vision, often in one eye only. Pain may be less than expected because the virus reduces corneal sensation.
• Treatment: antiviral drops, gels or tablets. For deeper disease, a specialist may add carefully controlled steroid drops together with antiviral cover. People with frequent recurrences may be advised long-term antiviral tablets, a strategy supported by the Herpetic Eye Disease Study.

Herpes zoster (shingles) affecting the forehead and nose can also involve the eye. A shingles rash near the eye, especially on the tip of the nose, needs prompt medical review and antiviral treatment.

Contact lenses: the biggest modifiable risk

Contact lenses are safe for millions of people when used correctly, but they reduce oxygen to the cornea and can trap microbes against it. Research consistently identifies overnight wear as the strongest risk factor for microbial keratitis; sleeping in lenses increases the risk many times over compared with daily wear. Read our detailed article on contact lens hygiene mistakes and our contact lens guide.

• Do not sleep or nap in lenses unless they are specifically approved for extended wear and your practitioner has advised it.
• Keep lenses away from water: no swimming, showering or hot tubs with lenses unless you wear tight goggles, and never rinse lenses or cases with tap water.
• Wash and dry your hands before handling lenses.
• Use fresh solution every time; never top up old solution.
• Rub and rinse reusable lenses as instructed, and air-dry the case upside down. Replace the case at least every three months.
• Replace lenses on schedule; daily disposables carry a lower risk of complications for many people.
• Never wear lenses when your eye is red or painful. Remove them and keep them and the case, as they may help the laboratory identify an organism.
• Buy cosmetic or coloured lenses only with a proper fitting from a qualified practitioner.

Endophthalmitis: infection inside the eye

Endophthalmitis is an infection of the fluids and tissues inside the eye. It is rare but one of the most serious emergencies in ophthalmology.

• Causes: most commonly after eye surgery, such as cataract surgery, or intravitreal injections; after penetrating eye injuries; and occasionally from infection spreading through the bloodstream (endogenous endophthalmitis), for example in people with diabetes, weakened immunity, intravenous lines or drug injection.
• Symptoms: increasing pain, redness, worsening vision and sometimes a layer of pus visible in the front of the eye, usually within days of surgery or injection, though some forms appear weeks later.
• Treatment: urgent injection of antibiotics directly into the eye after taking fluid samples, and sometimes vitrectomy surgery. Hours matter for the visual outcome.

Orbital and preseptal cellulitis

Cellulitis is a bacterial infection of soft tissues. Around the eye, doctors distinguish two types separated by a thin layer called the orbital septum.

• Preseptal (periorbital) cellulitis – infection of the eyelid and skin in front of the septum. The lids are red, swollen and tender, but vision and eye movements are normal. It is more common in children and is usually treated with antibiotics by mouth, with close follow-up.
• Orbital cellulitis – infection behind the septum, in the eye socket, most often spreading from the sinuses. Signs include pain on moving the eye, restricted or painful eye movements, double vision, bulging of the eye, reduced vision and fever. It requires hospital admission, intravenous antibiotics, scans and sometimes surgical drainage, because it can threaten vision and, rarely, spread to the brain.

A swollen eyelid in a child with a recent cold or sinus infection should always be checked by a doctor the same day, especially if the child has a fever or the eye cannot move normally.

Diagnosis and what to expect

At an eye clinic or emergency department, the doctor will check your vision, examine the eye with a slit lamp microscope and use fluorescein dye, which highlights damaged areas of the cornea under a blue light. Samples may be taken from the cornea, lenses or case. For suspected orbital cellulitis, a CT scan is usually arranged. Severe ulcers may require frequent visits, sometimes daily, until they are clearly improving.

After the infection is controlled, scarring may remain. Depending on its location and density, vision can sometimes be improved with glasses or rigid contact lenses, and occasionally a corneal transplant is needed.

Prevention checklist

• Follow contact lens hygiene rules carefully and avoid water contact with lenses.
• Wear protective eyewear for gardening, DIY, farming and sports; our page on eye safety at work and in sports explains suitable types.
• Do not use steroid eye drops without specialist supervision.
• Treat eyelid conditions such as blepharitis and manage dry eye.
• Keep diabetes well controlled, as it increases the risk of infection.
• Seek help early: a corneal ulcer treated on day one has a much better outcome than one treated on day four.

When to see a doctor: urgent warning signs

When in doubt, it is always better to be examined and reassured than to wait. For a broader overview of urgent problems, see our page on eye emergencies and first aid.