Corneal Infection

Overview

A corneal infection, also called infectious keratitis, is an infection of the cornea, the transparent dome at the front of the eye that focuses light. Because the cornea is clear and central to vision, infection there can quickly cloud sight and, if untreated, leave permanent scarring. When the infection causes an open sore, it is called a corneal ulcer.

Corneal infections can be caused by bacteria, viruses, fungi, or rarer organisms such as Acanthamoeba. They are most common in contact lens wearers and after eye injuries, because both can breach the cornea's protective surface and let organisms in. This is generally an urgent eye condition: an infection can progress over hours to days, so prompt treatment aimed at the specific cause gives the best chance of preserving vision.

The cornea has a remarkable ability to heal when treated early, but it has no blood vessels of its own and depends on tears, the surrounding tissue, and treatment to fight infection. A small, peripheral infection caught early may heal with little or no lasting effect, whereas a deep or central infection can leave a scar that blurs vision permanently. This is why any painful red eye, particularly in someone who wears contact lenses, should be taken seriously and assessed without delay rather than treated at home.

Symptoms

Symptoms usually affect one eye and can develop quickly. They include:

• Eye pain, often moderate to severe
• Redness
• Blurred or reduced vision
• Sensitivity to light
• Watering and discharge
• A white, grey, or cloudy spot on the cornea
• A feeling that something is in the eye

Any painful red eye with blurred vision, especially in a contact lens wearer, should be treated as an emergency and assessed the same day.

Common Causes

Different organisms can infect the cornea, usually after the eye's surface has been compromised:

• Bacteria: The most common cause, often linked to contact lenses or injury.
• Viruses: Especially herpes simplex, which can recur and scar the cornea.
• Fungi: Often after an injury involving plant material.
• Acanthamoeba: A water and soil organism linked to contact lenses and water exposure.

In most cases the cornea's surface is breached first, by a contact lens, a scratch, severe dryness, or eyelid disease, which allows organisms that are normally kept out to invade. Healthy tears and a smooth, intact corneal surface are powerful natural defenses, so anything that disrupts them raises the risk. This is why contact lens hygiene, prompt care for eye injuries, and treatment of chronic dry eye or eyelid inflammation all help prevent infection.

Risk Factors

• Contact lens wear, especially overnight use, poor hygiene, or water exposure
• Eye injury or foreign body
• Severe dry eye or eyelid inflammation
• Recent eye surgery
• A weakened immune system
• Misuse of steroid eye drops

Diagnosis

An ophthalmologist examines the cornea with a slit lamp microscope. To find the cause and guide treatment they may:

• Apply fluorescein dye to highlight an ulcer or damaged area
• Take a corneal scraping for culture and microscopy
• Use special stains or confocal microscopy in selected cases
• Review contact lens use, injury, and any rash suggesting herpes or shingles

The history is often as informative as the examination. Contact lens wear points toward bacterial or Acanthamoeba infection, an injury with plant material toward fungal infection, and a prior cold sore or a branching ulcer toward herpes. Severe pain that seems out of proportion to the eye's appearance can be a clue to Acanthamoeba. By combining these clues with the examination findings and, when needed, laboratory results, the doctor narrows down the likely cause and chooses the most appropriate treatment.

Treatment

Treatment is tailored to the organism and is usually managed by an eye specialist.

• Antibiotic drops for bacterial infection, often intensive at first.
• Antiviral medication for herpes-related infection.
• Antifungal drops or tablets for fungal infection, often for weeks.
• Specialized antiseptic drops for Acanthamoeba, often for months.
• Stopping contact lens wear until the eye has fully healed and an eye professional confirms it is safe to resume.

Because the different causes need very different drugs, identifying the organism, or at least the most likely one, is central to effective treatment. Doctors often begin broad treatment immediately and refine it once test results return. Frequent follow-up checks confirm the infection is responding and allow the plan to be adjusted. Most cases improve with prompt, targeted treatment, though a scar may remain, especially after central or deep infections. Severe infections that threaten the eye occasionally require a corneal transplant, either to treat the infection or later to restore vision lost to scarring.

Prevention

• Follow contact lens hygiene strictly and never sleep in lenses unless approved
• Keep lenses and eyes away from water; remove lenses before swimming or showering
• Wear eye protection during activities that risk injury
• Manage dry eye and eyelid disease with your eye doctor
• Do not use steroid eye drops without medical guidance
• Seek care promptly for any eye injury or painful red eye

When to See a Doctor

A corneal infection is an eye emergency. Seek same-day care if you have:

• A red, painful eye, especially as a contact lens wearer
• Blurred vision or a white spot on the cornea
• Light sensitivity with watering or discharge
• Symptoms worsening over hours

Do not wait to see if it settles. Early, targeted treatment offers the best chance of saving vision.

Related Topics

Frequently Asked Questions

References

1. American Academy of Ophthalmology. Bacterial Keratitis.
2. National Eye Institute (NEI). Keratitis.
3. Centers for Disease Control and Prevention (CDC). Contact Lenses and Eye Infections.
4. MedlinePlus, U.S. National Library of Medicine. Corneal injuries and infections.