Microbial keratitis (corneal infections)

Corneal infections are named after the type of germ causing them. The main groups include:

• Bacterial keratitis: caused by bacteria. This is the usual cause of microbial keratitis in UK practice and is often associated with wearing contact lenses².
• Fungal keratitis: caused by fungi, including moulds such as Aspergillus and Fusarium, and yeasts such as Candida. It may follow an injury involving plant material or occur in an eye with an already damaged surface⁴.
• Acanthamoeba keratitis: caused by a microscopic amoeba found in water and soil. It is particularly associated with contact lens wear and exposure to water, including showering or swimming in lenses⁵.
• Viral keratitis: can be caused by the herpes simplex virus, which also causes cold sores. The virus can remain in the body and reactivate, so infections may return⁶.

Damage to the protective surface of the cornea can make it easier for germs to cause an infection. Factors that increase the risk include⁷:

• Contact lens wearing: especially sleeping in lenses, wearing them for longer than recommended, or not cleaning and storing them correctly⁸.
• Water exposure while wearing lenses: including swimming, showering, or rinsing lenses in tap water. This is a particular risk for Acanthamoeba infection⁵.
• Eye injuries: a scratch from a thorn, branch or other plant material can introduce fungi into the cornea⁴.
• Existing eye problems: dry eye, poor eyelid closure, previous eye surgery or other damage to the eye surface can increase susceptibility².
• Reduced immunity or steroid use: a weakened immune system and corticosteroid medicines can increase the risk of fungal eye infection⁴.

Symptoms often affect one eye and may include²:

• Eye pain and redness.
• Blurred or reduced vision.
• Sensitivity to light.
• Watering or discharge.
• A gritty feeling, as though something is in your eye.
• A white or cloudy spot on the clear front surface of your eye¹.

Do not try to identify the type of infection yourself. Fungal and other corneal infections can have similar symptoms, and prompt examination is important. If your eye becomes more painful or red, your vision worsens, or a white spot gets bigger during treatment, seek urgent advice from your eye-care team or attend A&E^4,1.

An eye specialist will examine your cornea using a slit lamp, a microscope with a bright light. They may ask about contact lenses, recent eye injuries and your symptoms. In some cases, they will numb your eye with anaesthetic drops and gently collect a small sample from the affected cornea, known as a corneal scrape^9,1.

The sample can be examined under a microscope or grown in a laboratory to identify the germ. Fungal infections can be difficult to diagnose, and specialists may also use tests that detect genetic material, such as PCR, or detailed imaging called confocal microscopy⁴.

Treatment may start before all results are available and can be adjusted when the results return or depending on how your eye responds. Tell your eye-care team if your symptoms are not improving^9,1.

Current treatments:

Treatment fundamentally depends on the germ causing the infection and how severely your eye is affected:

• Bacterial infections: usually need antibiotic eye drops. Drops may be needed very frequently, including through the night in severe cases¹.
• Fungal infections: need antifungal medicines rather than antibiotics alone. Treatment usually involves antifungal eye drops; some people also need tablets or specialist procedures^2,7.
• Acanthamoeba infections: need specialist antiseptic eye drops. Treatment can take months and must be closely monitored⁹.
• Herpes simplex infections: are treated with antiviral medicines, such as eye drops, ointment or tablets. Some people need longer-term treatment to help prevent recurrences⁶.

Severe infections may require hospital care. If a fungal infection does not respond to medicines, surgery, including a corneal transplant, may be needed. A transplant may also be considered for sight-limiting scarring after some corneal infections^2,7,9.

Use your prescribed drops exactly as directed and attend follow-up appointments. Do not restart contact lenses until your eye-care team says it is safe. Steroid eye drops are only suitable in selected circumstances under specialist supervision; they are not a treatment to start yourself for a suspected infection^1,9.

Potential treatments and better diagnosis:

Research is exploring ways to improve the treatment of fungal keratitis, including more targeted delivery of antifungal medicines and whether corneal cross-linking could help alongside medication. These approaches need careful evaluation; corneal cross-linking is not an established routine treatment for fungal keratitis⁷.

A potential new treatment for bacterial keratitis

At Sight Research UK, we have supported Dr Imran Mohammed and his team at Cardiff University to explore a new way of treating bacterial keratitis. Their approach uses synthetic peptides inspired by the eye’s natural infection-fighting defences. The team developed a potential treatment called SMP16, based on a natural defence molecule called human cathelicidin¹¹.

The aim is to tackle bacterial biofilms: protective layers that can make infections harder to treat. In early laboratory studies using a corneal infection model, SMP16 penetrated these biofilms and killed bacteria more effectively than moxifloxacin, a commonly used antibiotic, even at lower concentrations. These are encouraging experimental findings, rather than evidence that the treatment works better in patients.

If further studies confirm these benefits, the approach could mean patients need less medicine or fewer doses. This could make treatment easier to manage at home and potentially reduce the need for a hospital stay. However, further testing in living tissue and clinical trials would be needed to establish its safety and effectiveness in people. SMP16 remains a potential future treatment, not an established option for patients.

Faster diagnosis of fungal keratitis

Better diagnosis is another important route to protecting sight. In a published feasibility study, researchers at the University of Edinburgh and Aravind Eye Hospital in India tested a lateral flow device for identifying Aspergillus in corneal samples. Results from both scrape and swab samples were promising, but this was an early diagnostic study, not proof that a test can detect every fungal infection or improve outcomes in routine care¹⁰.

At Sight Research UK, we have supported work to develop a lateral flow test led by Dr Beth Mills that can detect a wider range of fungi. Using a format familiar from COVID-19 tests, the aim is a simple test that could help healthcare professionals choose the right treatment sooner. The project described in our research material includes laboratory testing, clinical evaluation with partners in India and development of a smartphone-based reader. These research approaches should not be presented as home tests or substitutes for urgent clinical assessment.

You cannot prevent every corneal infection, but good contact lens care and protecting your eyes from injury can reduce your risk^8,4.

• Wash and dry your hands thoroughly before touching your lenses⁸.
• Keep lenses away from water. Take them out before swimming, showering or bathing, and never rinse or store them in tap water⁸.
• Do not sleep in your lenses. Follow your contact lens practitioner’s advice on wearing time and replacement. Never reuse daily disposable lenses⁸.
• Care for reusable lenses properly. Use the recommended cleaning and disinfecting solution, keep the case clean and replace it regularly as advised⁸.
• Do not wear lenses in a red or sore eye. Remove them and seek prompt advice rather than continuing to wear them⁸.
• Wear suitable protective eyewear when gardening, farming or doing work where plant material could injure your eyes⁴.

Acting early matters. If you develop pain, redness, light sensitivity or changes to your vision, get urgent eye-care advice. Prompt diagnosis and appropriate treatment offer the best chance of protecting your sight^2,3.

This information is a general guide and does not replace advice from your eye-heath professional.