A corneal ulcer is an open sore on the cornea, the clear, dome-shaped surface that covers the front of your eye. It’s a medical emergency that can cause permanent vision loss if left untreated. Most corneal ulcers are caused by infections, particularly in contact lens wearers, though injuries, severe dry eye, and inflammatory conditions can also trigger them.
How a Corneal Ulcer Forms
Your cornea has several thin layers that protect the interior of your eye and focus incoming light. The outermost layer, called the epithelium, acts as a barrier against bacteria, viruses, and fungi. When that barrier is breached, whether by a scratch, a poorly fitting contact lens, or chronic dryness, microorganisms can invade the deeper tissue. The immune system responds with inflammation, and the resulting damage creates an ulcer: a crater-like defect that eats into the cornea’s structure.
Because the cornea is responsible for roughly two-thirds of your eye’s focusing power, even a small ulcer in the central zone can distort your vision. If the infection or inflammation goes deep enough, it can thin the cornea to the point of perforation, which is a sight-threatening emergency requiring surgery.
Common Causes
Bacteria are the most frequent culprits. The species most often identified in corneal ulcers include Staphylococcus aureus, Pseudomonas aeruginosa, and Streptococcus pneumoniae. Pseudomonas infections are particularly aggressive and progress fast, often within 24 to 48 hours.
Viruses, fungi, and parasites also cause corneal ulcers. Herpes simplex keratitis is a recurring viral infection that can flare up with stress, sun exposure, or anything that weakens the immune system. Fungal ulcers tend to develop after eye injuries involving plant material or organic matter. Acanthamoeba, a parasite found in water, causes a painful and difficult-to-treat infection almost exclusively in contact lens wearers, especially those who rinse or store lenses in homemade solutions or tap water.
Not all corneal ulcers are infectious. Autoimmune conditions like rheumatoid arthritis and lupus can trigger a type of ulceration at the edges of the cornea. Severely dry eyes, eyelids that don’t close completely (as in Bell’s palsy), and foreign bodies lodged under the lid can all break down the cornea’s protective surface and set the stage for an ulcer.
Contact Lenses and Risk
Contact lens wear is the single biggest risk factor for corneal ulcers in developed countries. A CDC analysis of over 1,000 contact lens-related corneal infections reported to the FDA between 2005 and 2015 found that about 25% of cases involved clearly modifiable behaviors. The most common: sleeping in lenses (extended wear accounted for 11.3% of reports, occasional overnight wear another 7%), wearing lenses longer than prescribed (7.9%), swimming in lenses (0.9%), and storing lenses in tap water (0.8%).
The risk isn’t just theoretical. Sleeping in contact lenses, even occasionally, deprives the cornea of oxygen and creates a warm, moist environment where bacteria thrive. If you wear contacts, the simplest way to reduce your risk is to take them out every night, replace them on schedule, and never let tap water touch them.
Symptoms to Watch For
A corneal ulcer typically causes intense eye pain that feels disproportionate to what you’d expect from a “red eye.” Other hallmarks include:
- A visible white or grayish spot on the cornea. This is the ulcer itself, and you may be able to see it in the mirror.
- Severe sensitivity to light that makes it hard to keep the affected eye open.
- Excessive tearing or discharge, which may be thick and yellowish if bacterial.
- Blurred vision, especially if the ulcer sits near the center of the cornea.
- A feeling that something is stuck in the eye.
These symptoms overlap with pink eye (conjunctivitis), but there are key differences. Pink eye usually causes mild irritation, gritty discomfort, and redness without a white spot on the cornea. A corneal ulcer causes sharper pain, more light sensitivity, and often a noticeable decline in vision. If you see a white or cloudy spot on your eye, or if the pain is severe enough that you can’t comfortably open your eye in normal light, treat it as urgent.
How It’s Diagnosed
An eye doctor will examine the cornea using a slit lamp, a specialized microscope that provides a magnified, cross-sectional view of each corneal layer. To make the ulcer easier to see, they’ll apply fluorescein dye as eye drops. The dye pools in any area where the surface is damaged, highlighting the ulcer’s size, depth, and location under blue light.
If the ulcer is large or doesn’t respond to initial treatment, the next step is identifying the specific organism. The doctor numbs your eye and gently scrapes a tiny sample from the ulcer’s surface. That sample is cultured in a lab to determine whether bacteria, fungi, a virus, or a parasite is responsible. For suspected herpes infections, a PCR test can detect the virus’s DNA directly from the scraping. Knowing exactly what’s causing the infection guides the choice of medication and can significantly affect the outcome.
Treatment
Treatment depends on the cause, but for bacterial ulcers, it centers on antibiotic eye drops, often given on a demanding schedule. In severe cases, drops are administered every hour around the clock, including overnight, for the first day or two. The goal is to saturate the cornea with medication and halt the infection before it penetrates deeper. As the ulcer responds, the frequency is tapered based on visible improvement: the edges of the ulcer soften, the white infiltrate shrinks, swelling decreases, and pain eases.
For smaller or less severe infections, a single antibiotic drop (typically a fluoroquinolone) may be sufficient. Fungal ulcers require antifungal drops, which generally need a longer course of treatment because fungi are slower to clear. Acanthamoeba infections are notoriously stubborn and can take weeks to months of intensive treatment. Herpes-related ulcers are treated with antiviral medications, and managing flare-ups over time is part of the long-term plan.
Severe cases may require hospitalization so the hourly drop schedule can be maintained by nursing staff. Systemic antibiotics are rarely needed but may be added if the infection has spread beyond the cornea into surrounding tissue, or if the cornea is at risk of perforating.
When Surgery Becomes Necessary
Most corneal ulcers heal with medication alone, but some progress to the point where the cornea thins dangerously or perforates. For very small perforations (under 2 mm), doctors can seal the hole with a medical-grade tissue adhesive, essentially a biological glue applied directly to the defect. For microperforations smaller than 0.5 mm, medications that reduce fluid production inside the eye may be enough to let the cornea seal on its own.
Larger perforations, or small ones surrounded by extensive dead tissue, require a corneal transplant. A full-thickness transplant (penetrating keratoplasty) replaces the entire damaged section with donor tissue and is the standard approach when active infection needs to be eliminated or when the perforation is larger than 2 mm with significant tissue loss. A partial-thickness transplant (lamellar keratoplasty) is an option when only some layers of the cornea are involved. Eye specialists recommend intervening before perforation occurs when possible, because repairing a thinning cornea is far easier than managing one that has already ruptured.
Long-Term Complications
Even after successful treatment, a corneal ulcer often leaves a scar. If that scar sits in the center of the cornea, it can permanently reduce vision by blocking or distorting light. The severity ranges from mild blurriness to significant vision loss, depending on the ulcer’s size, depth, and location.
Other potential complications include astigmatism from irregular healing, glaucoma from prolonged inflammation, cataracts, and recurrent corneal erosions where the healed surface periodically breaks down again. In rare cases, infection can spread to the interior of the eye (endophthalmitis), which threatens the entire eye. The single most important factor in limiting these outcomes is how quickly treatment begins. Corneal ulcers that are caught early and treated aggressively have a far better chance of healing with minimal scarring than those left to progress for days.