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At a glance
- A corneal ulcer is an open sore on the cornea, the clear front window of the eye, usually caused by infection.
- It is a potentially sight-threatening emergency that needs prompt treatment.
- Contact-lens misuse is a leading cause in Singapore.
- Warning signs include a painful red eye, light sensitivity and blurred vision.
What a corneal ulcer is
The cornea is the clear, dome-shaped front surface of the eye that lets light in and helps focus it. A corneal ulcer is an open sore — a break in this surface with underlying inflammation or infection — that can rapidly threaten sight. Because the cornea has no blood vessels and relies on a thin protective tear film, an infection that takes hold can spread and deepen quickly. Left untreated, an ulcer can scar the cornea, cloud vision permanently, or in severe cases perforate the eye. This is why any suspected corneal ulcer is treated as an urgent, sight-threatening problem rather than a minor irritation that will settle on its own.
Symptoms
A corneal ulcer usually causes significant eye pain, marked redness and watering, together with blurred or reduced vision and strong sensitivity to light. Many people feel as though something is stuck in the eye, and there may be discharge or a sticky, gritty sensation. Sometimes a whitish or greyish spot can be seen on the normally clear cornea, which reflects the ulcer itself. Symptoms typically come on over hours to a few days and tend to worsen — not improve — without treatment. A contact-lens wearer whose eye becomes red and painful should treat this as a warning sign and never try to push through the discomfort by wearing the lens longer.
What causes a corneal ulcer
Most corneal ulcers are caused by infection. Bacteria are the commonest culprit, but in this region fungal infections and the parasite Acanthamoeba are also important causes, and both can be aggressive and difficult to treat. Acanthamoeba in particular is strongly linked to contact-lens use combined with water exposure, such as swimming or showering in lenses. The cold-sore (herpes simplex) virus can also cause recurring corneal ulcers. Non-infective triggers include injury or a scratch to the cornea, a foreign body, severe dry eye, and problems with eyelid closure that leave the surface exposed and unprotected. In many cases the infection follows a break in the corneal surface that lets organisms enter — which is why contact-lens misuse, injuries and dry eyes are such frequent starting points.
Who is at higher risk
Contact-lens wearers are at the highest risk, and the risk rises sharply with certain habits: sleeping or napping in lenses that are not designed for overnight wear, overwearing lenses beyond their intended schedule, poor hand and lens hygiene, topping up rather than replacing solution, and any water exposure — swimming, showering or using a hot tub — while wearing lenses. Other people at greater risk include those with severe dry eye, previous eye surgery or a past corneal injury, reduced eyelid closure or facial-nerve weakness, a history of cold-sore eye infections, and anyone using long-term steroid eye drops or with a weakened immune system. Being in one of these groups does not mean an ulcer will develop, but it makes early attention to any red, painful eye especially important.
How it is diagnosed
Diagnosis needs an urgent, in-person eye examination. An eye specialist examines the cornea closely with a slit lamp — a special microscope — often after placing a harmless dye that highlights the ulcer and any surface break. To find the exact cause and guide targeted treatment, the specialist may gently scrape a small sample from the ulcer for laboratory tests, which can identify whether bacteria, fungi or a parasite are responsible. Contact-lens wearers are usually asked to bring their lenses, case and solution, as these can also be tested. Identifying the organism matters because bacterial, fungal and parasitic ulcers each need different medicines.
Treatment
Treatment is urgent and centres on intensive prescribed antimicrobial eye drops — antibiotic, antifungal or antiparasitic depending on the cause — which are often started very frequently, sometimes hourly at first, including through the night. Contact-lens wear is stopped completely until the eye has fully healed and the specialist gives the all-clear. Close, repeated follow-up is essential to confirm the ulcer is responding and to adjust treatment if it is not. More severe or advanced ulcers may need hospital admission for closer monitoring and intensive drops. Delay is the main enemy: a late-treated ulcer is more likely to leave a scar and reduce vision. In serious cases where the ulcer perforates or leaves dense scarring, surgery — including a corneal transplant — may eventually be needed to protect or restore sight. Started early, treatment greatly improves the outcome.
Contact-lens safety to prevent corneal ulcers
Since contact-lens misuse is a leading cause of corneal ulcers in Singapore, safe habits dramatically reduce the risk. Wash and dry your hands before handling lenses, never sleep in lenses unless they are specifically designed and approved for overnight wear, and do not top up old solution — empty the case and use fresh solution each time. Replace lenses and cases on the schedule you were given, and never rinse lenses or the case in tap water. Crucially, avoid wearing lenses while swimming, showering or using a hot tub, as waterborne organisms can cause severe, hard-to-treat infections. Give your eyes regular breaks from lenses, keep to any prescribed wear time, and have your fit and eye health checked as advised. Anyone with a red, painful eye while wearing lenses should remove them immediately and seek same-day care.
Recovery and long-term outlook
With prompt, intensive treatment most corneal ulcers heal, but the outlook depends on the size, depth and cause of the ulcer and how quickly treatment began. A superficial ulcer treated early may heal with little effect on vision, while a deeper or central ulcer can leave a scar that blurs sight. Follow-up appointments are important to confirm the infection is clearing, to taper medication safely, and to watch for any recurrence. If scarring significantly affects vision after healing, options such as a corneal transplant may be considered later to restore clarity. Preventing a repeat — particularly by reviewing contact-lens habits — is an essential part of recovery.
When to see a doctor
Seek urgent, same-day care for a painful red eye with light sensitivity or blurred vision, particularly if you wear contact lenses. Do not wait to see if it settles, and remove your lenses and bring them with you. A corneal ulcer can threaten sight and should not be left overnight. In Singapore you can attend an eye A&E such as the Singapore National Eye Centre, or ask your doctor for urgent referral to an eye specialist; reliable general guidance is also available on HealthHub.
Common questions
Is a corneal ulcer an emergency?
Yes. It can rapidly threaten vision and needs prompt assessment and treatment by an eye specialist.
Can contact lenses cause a corneal ulcer?
Yes. Overwear, sleeping in lenses, poor hygiene and swimming in lenses are major risk factors.
Will a corneal ulcer leave a scar?
It can, especially if deep or treated late; the effect on vision depends on the scar’s size and location.
Related conditions & guides
Sources
- Singapore National Eye Centre — corneal infection.
- American Academy of Ophthalmology — corneal ulcer.
- HealthHub Singapore — contact lens safety.
This article is for general information only and does not replace a consultation with a qualified eye-care professional. Please seek personalised advice for your own eyes.