Corneal Infection (Infectious Keratitis)

What happens in a corneal infection

The cornea is a thin, transparent layer with no blood vessels and many pain nerves. It is protected by tears, blinking and a tough outer surface (the epithelium). Infection usually needs a break in that surface, from a scratch, a contact lens, dry eye or a damaged cornea. Microbes then invade and destroy corneal tissue. Without treatment, an area of tissue loss (a corneal ulcer) forms, heals with a scar that can blur vision permanently, or in severe cases perforates the eye.

This page focuses on infection specifically. For non-infectious causes of an inflamed cornea, such as dry eye or UV injury, see keratitis.

Symptoms

• Eye pain, often severe, or a feeling that something is stuck in the eye
• Redness, mainly around the colored part (iris)
• Sensitivity to light
• Blurred or reduced vision
• Watery or pus-like discharge
• A white, gray or cream spot on the cornea, visible in a mirror in larger infections
• Swollen eyelids

It usually affects one eye. Conjunctivitis, by contrast, often affects both eyes, causes little pain and does not reduce vision.

Types of corneal infection

Causes and risk factors

• Contact lenses: the single biggest risk. Overnight wear raises the risk many times over. Rinsing or storing lenses in tap water, topping up old solution, and swimming or showering in lenses are well-known triggers.
• Eye injury: scratches, especially from plants or soil.
• Eye surface disease: severe dry eye, eyelids that do not close, previous corneal surgery.
• Steroid eye drops, used without supervision.
• Weakened immunity and diabetes.

How it is diagnosed

An eye doctor examines the eye with a slit lamp microscope and fluorescein dye, which makes damaged surface glow green. They measure the size and depth of the infiltrate and look for inflammation or pus in the front chamber.

For anything more than a small, peripheral infiltrate, the doctor takes a corneal scraping under numbing drops to identify the organism by microscopy, culture and sometimes PCR testing. Contact lenses and their case may be cultured too. Confocal microscopy, where available, can show fungi or Acanthamoeba cysts directly.

Treatment

Treatment begins the same day, often before culture results return, and is adjusted once the organism is known.

• Bacterial: fortified or fluoroquinolone antibiotic drops, initially every hour day and night for the first 24 to 48 hours.
• Herpes simplex: antiviral eye gel or oral antivirals. Long-term oral antivirals may be used to prevent recurrences.
• Fungal: antifungal drops such as natamycin, sometimes with oral antifungals; treatment lasts weeks.
• Acanthamoeba: specialized anti-amoebic drops for months.
• Supportive care: dilating drops ease pain from iris spasm; pain relievers by mouth (follow the label dose).
• Steroid drops: may be added later in some bacterial infections to limit scarring, but only by an eye specialist, because they can worsen fungal and herpes infections.

Stop wearing contact lenses until the eye doctor says the cornea has fully healed, and throw away the lenses and case you were using.

If the infection does not respond, options include corneal cross-linking, an amniotic membrane graft or a corneal transplant (keratoplasty), which is also used later to restore vision through a dense scar.

Complications

• Corneal scarring and permanent blurred vision
• Irregular astigmatism
• Corneal thinning or perforation
• Spread inside the eye (endophthalmitis), which is rare but serious
• Loss of the eye in the most severe cases

Prevention for contact lens wearers

• Do not sleep in lenses unless your eye doctor has prescribed extended wear.
• Never let lenses touch tap water; do not swim or shower in them.
• Use fresh solution every time and replace the case every 1 to 3 months.
• Wash and dry your hands before handling lenses.
• Remove lenses and see an eye doctor promptly if your eye becomes red or painful.

Frequently asked questions

How do I know if my cornea is infected?

Warning signs are a painful red eye, light sensitivity, blurred vision, discharge and sometimes a white spot on the clear front of the eye. Pain and blurring separate it from simple conjunctivitis. Contact lens wearers with these symptoms should remove their lenses and see an eye doctor the same day.

How long does a corneal infection take to heal?

A mild bacterial infection usually starts improving within 2 to 3 days of intensive drops and heals over 1 to 3 weeks. Fungal infections can take several weeks to months, and Acanthamoeba infections often need 6 months or more of treatment.

Can a corneal infection cause blindness?

Yes. Untreated or severe infections can scar the cornea or perforate the eye, causing permanent vision loss. Corneal infection is a leading cause of preventable vision loss worldwide. Prompt treatment greatly improves the outcome.

Is a corneal infection contagious?

The cornea infection itself is not usually spread by casual contact. Herpes viruses can spread from cold sores, and bacteria on hands or towels can reach the eye. Wash hands often and do not share towels or eye drops.

Can I treat a corneal infection with over-the-counter drops?

No. Corneal infections need prescription antimicrobial drops chosen by an eye doctor, often after a scraping test. Over-the-counter redness or lubricating drops can mask symptoms and delay treatment.