Bacterial keratitis is a severe infection of the cornea, the clear, dome-shaped outer layer at the front of the eye. It occurs when bacteria invade corneal tissue, potentially leading to significant damage if not addressed promptly. Immediate evaluation and care from an ophthalmologist are essential to prevent vision impairment. Early intervention is crucial due to the cornea’s role in focusing light for clear vision.
Causes and Risk Factors
Wearing contact lenses is the most common factor contributing to bacterial keratitis, especially with inadequate hygiene. Sleeping in contact lenses significantly increases risk by reducing corneal oxygen supply and creating a favorable environment for bacterial growth. Improper cleaning, disinfection, using expired solutions, or extending wear schedules also elevate infection likelihood. Rinsing or storing lenses in tap water or homemade saline solutions introduces microorganisms like Pseudomonas aeruginosa.
Eye injuries, even minor abrasions, can break down the cornea’s protective barrier, allowing bacteria to enter. Recent eye surgery, such as cataract removal or LASIK, can temporarily compromise the eye’s natural defenses, increasing susceptibility during healing. Pre-existing eye conditions, including severe dry eye, eyelid disorders preventing complete lid closure, or chronic blepharitis, increase susceptibility due to compromised tear film or persistent inflammation. Contaminated eye drops, makeup, or shared towels can also introduce bacteria to the ocular surface.
Signs and Symptoms
Bacterial keratitis presents with a sudden onset of symptoms that can worsen rapidly. Patients experience severe eye pain, often described as a persistent ache or sharp sensations. Significant eye redness is a prominent indicator, appearing as deep crimson around the iris and pupil. Vision becomes blurred, and patients report sensitivity to light (photophobia), making bright environments difficult to tolerate.
A foreign body sensation, like grit, often persists despite blinking. The eye may produce discharge, which can cause eyelids to stick together, especially upon waking. These symptoms typically affect one eye and warrant immediate medical evaluation.
Diagnosis Process
Diagnosing bacterial keratitis begins with a comprehensive eye examination by an ophthalmologist. The doctor uses a slit-lamp microscope, which provides a magnified, three-dimensional view of the cornea and other anterior eye structures. This allows for detailed inspection of the corneal surface to identify the size, shape, and depth of any corneal infiltrate or ulcer. White or yellowish spots on the cornea indicate bacterial presence and inflammation.
To confirm the diagnosis and identify the specific bacteria, the doctor takes a sample from the infected area. This procedure, known as a corneal scraping or culture, involves gently rubbing a sterile instrument over the corneal surface to collect a specimen. The sample is then sent to a laboratory for microscopic examination and bacterial culture. Lab analysis helps determine the type of bacteria, guiding the selection of the most effective antibiotic treatment.
Treatment Protocols
Treatment for bacterial keratitis involves intensive application of antibiotic eye drops. These drops are administered frequently at the beginning of treatment, sometimes hourly, to achieve high concentrations in the cornea. Initial treatment involves broad-spectrum antibiotics, effective against a wide range of common bacteria, to immediately combat the infection while awaiting lab results.
Once the specific bacterium is identified through culture, the ophthalmologist may switch to a more targeted antibiotic. In some cases, after the acute infection is controlled, doctors may introduce corticosteroid eye drops. These drops are used cautiously and only when the infection has significantly resolved, as they can suppress the immune response and potentially worsen an active bacterial infection. Steroid drops reduce inflammation and minimize corneal scarring, which can otherwise impair vision. Adhering to the prescribed dosage and schedule for all eye drops is vital for successful treatment and preventing complications.
Potential Complications
Delayed or ineffective treatment of bacterial keratitis can lead to serious complications that may permanently affect vision. A common consequence is the development of a corneal ulcer, an open sore on the cornea resulting from tissue breakdown due to the infection. As the ulcer heals, it often leaves behind permanent corneal scarring, which appears as an opaque area on the normally clear cornea, obstructing light entry and causing persistent vision impairment. The extent of vision loss depends on the size and location of the scar, with centrally located scars having a more significant impact.
In severe and untreated cases, the infection can progress to cause corneal perforation, where a hole forms through the entire thickness of the cornea. This is an ophthalmic emergency that can lead to a sudden decrease in intraocular pressure and potentially allow bacteria to spread inside the eye, leading to a more widespread and severe infection called endophthalmitis. Endophthalmitis is a severe condition that can result in complete loss of the eye or permanent blindness. If significant corneal scarring occurs and severely impairs vision, a corneal transplant, a surgical procedure to replace the damaged cornea with healthy donor tissue, may be necessary to restore sight.