Bacterial Keratitis

Overview

Bacterial keratitis is an infection of the cornea, the clear dome of tissue at the front of the eye. Bacteria invade the corneal surface and multiply, causing inflammation, ulceration, and sometimes a visible white or grey spot on the cornea. Because the cornea is responsible for focusing light, even a small infection can blur vision, and a severe or untreated one can leave permanent scarring.

This is an urgent eye condition. Bacterial keratitis can progress over hours to days, and prompt treatment with antibiotic eye drops is needed to clear the infection and protect sight. It is one of the most common causes of corneal blindness worldwide and is strongly associated with contact lens wear.

Under normal circumstances the cornea is well protected by the eyelids, the tear film, and its own smooth, intact surface. Bacteria usually take hold only when this protection is broken, most often by a contact lens that has been worn too long, slept in, or poorly cleaned, or by a scratch or foreign body. Some bacteria, such as Pseudomonas, can multiply rapidly and cause serious damage in a short time, which is why even early symptoms should not be ignored. The good news is that, treated promptly and correctly, most bacterial corneal infections clear without losing useful vision.

Symptoms

Symptoms usually come on quickly and affect one eye. They include:

• Eye pain, often moderate to severe
• Redness of the eye
• Blurred or reduced vision
• Sensitivity to light (photophobia)
• Watering and thick or pus-like discharge
• A white or grey spot on the normally clear cornea
• A feeling that something is in the eye

Any of these symptoms in a contact lens wearer, or rapidly worsening eye pain and redness in anyone, should be treated as an emergency and assessed the same day.

Causes

Bacterial keratitis develops when bacteria breach the cornea's protective surface. Common bacteria include Staphylococcus, Streptococcus, and Pseudomonas aeruginosa, the last of which is especially aggressive and linked to contact lenses.

• Contact lens wear: Sleeping in lenses, poor cleaning, topping up old solution, or wearing lenses too long damages and contaminates the cornea.
• Eye injury: A scratch, abrasion, or foreign body can let bacteria in.
• A pre-existing eye surface problem: Severe dry eye, eyelid disease, or previous corneal damage.

Risk Factors

• Wearing contact lenses, especially overnight or extended-wear lenses
• Poor lens hygiene or swimming and showering in lenses
• Recent corneal injury or surgery
• Chronic dry eye or eyelid inflammation
• A weakened immune system
• Misuse of steroid eye drops

Diagnosis

An eye specialist (ophthalmologist) examines the eye with a slit lamp, a microscope that magnifies the cornea. To identify the bacteria and guide treatment, they may:

• Apply a dye such as fluorescein to highlight the ulcer or damaged area
• Take a scraping or swab of the cornea for laboratory culture in moderate or severe cases
• Measure how deep and large the infection is

Distinguishing bacterial infection from viral or fungal causes is important because treatment differs, and the history often helps: contact lens wear points toward bacteria, an injury with plant material toward fungi, and a prior cold sore or branching ulcer toward herpes. In milder cases, treatment may be started based on the examination alone, while moderate or severe infections are usually sampled first so the responsible bacterium and the antibiotics it responds to can be identified. The eye is then reviewed frequently to make sure it is improving.

Treatment

Treatment must begin promptly and is usually managed by an ophthalmologist.

• Antibiotic eye drops: Intensive drops, sometimes used every hour day and night at first, are the mainstay. Broad-spectrum antibiotics are started before culture results return.
• Stopping contact lens wear: Lenses are removed and not worn until the eye has fully healed and is cleared by a doctor.
• Close monitoring: Frequent reviews ensure the infection is responding; treatment is adjusted if needed.
• Supportive care: Pain relief and, later, drops to reduce inflammation may be added under specialist guidance.

The intensive early drop schedule, sometimes hourly through the day and night, can be demanding but is important to bring the infection under control quickly. As the eye improves, the frequency is gradually reduced. It is essential to keep using the drops as directed and to attend every follow-up, even once symptoms ease, because stopping too soon can let the infection return. Most cases resolve with prompt treatment, though a small scar may remain, which matters most if it sits over the center of the cornea. Severe or central infections occasionally need a corneal transplant, either during the infection or later to improve vision affected by scarring.

Prevention

• Wash and dry your hands before handling contact lenses
• Never sleep in lenses unless they are specifically approved for it
• Use fresh solution each time and never top up old solution or use water
• Avoid swimming, showering, or using hot tubs while wearing lenses
• Replace lenses and cases as directed and attend regular eye checks
• Seek care promptly for any eye injury or red, painful eye

When to See a Doctor

Bacterial keratitis is a medical emergency for the eye. Seek same-day care from an eye doctor or emergency service if you have:

• A red, painful eye, especially if you wear contact lenses
• Blurred vision or a white spot on the cornea
• Light sensitivity with watering or discharge
• Symptoms that are getting worse over hours

Do not wait to see if it settles on its own. Early antibiotic treatment greatly improves the 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.