Microbial keratitis is an infection of the cornea, the transparent, dome-shaped layer that covers the front of the eye. This condition occurs when the cornea becomes inflamed by microorganisms like bacteria, viruses, fungi, or parasites that breach its natural defenses. The resulting infection can be serious, potentially leading to complications that affect vision if not addressed promptly.
Causative Agents and Risk Factors
Microbial keratitis is triggered by microorganisms that successfully invade the cornea. Bacterial infections are the most frequent, often caused by species such as Pseudomonas aeruginosa and Staphylococcus aureus. Fungal agents, including Aspergillus and Fusarium, can also cause keratitis, as can the Herpes Simplex Virus. A particularly resilient type is caused by the amoeba Acanthamoeba, a parasite found in water and soil.
The single greatest risk factor for developing microbial keratitis is the use of contact lenses, and the risk increases significantly with improper hygiene. Sleeping in contact lenses, especially those not approved for overnight use, elevates the risk five to ten-fold. Other dangerous practices include failing to properly disinfect lenses, using tap water to rinse or store them, and wearing them beyond their recommended replacement schedule.
Beyond contact lens misuse, other factors can make an individual more susceptible to a corneal infection. Any injury to the eye, even a minor scratch, can create an opening for microbes to enter. Exposure to contaminated water sources like swimming pools or lakes while wearing contacts is another significant risk. A weakened immune system, from a medical condition or certain medications, also heightens the risk.
Signs and Symptoms
The onset of microbial keratitis is often sudden, with symptoms that can rapidly become severe. A primary indicator is significant eye pain, accompanied by intense redness in the white of the eye. Vision can become blurry or decrease noticeably, and individuals often develop a strong sensitivity to light, a condition known as photophobia.
Many people also experience the persistent feeling that there is a foreign object lodged in their eye. This sensation can be coupled with excessive tearing or a noticeable discharge from the eye, which may be watery or pus-like. Given the speed at which these symptoms can worsen, it is important to seek medical attention immediately.
Diagnosis and Medical Evaluation
A definitive diagnosis of microbial keratitis is performed by an ophthalmologist. The evaluation begins with a visual acuity test to measure any decline in vision. This is followed by a slit-lamp examination, which uses a high-powered microscope for a detailed, magnified view of the cornea and other structures at the front of the eye.
To better visualize any damage, the ophthalmologist may apply a special dye called fluorescein stain to the eye’s surface. This yellow-orange dye highlights any abrasions, ulcers, or areas of cell loss on the cornea under a blue light, revealing the extent of the infection.
To ensure the treatment is effective, the doctor must identify the specific microbe causing the infection. This is accomplished through a corneal scraping. During this procedure, the doctor numbs the eye with anesthetic drops and then uses a sterile instrument to collect a sample of cells from the affected cornea. This sample is sent to a laboratory for analysis to determine if the cause is bacterial, fungal, viral, or parasitic.
Treatment Approaches
The treatment for microbial keratitis is highly dependent on the specific microorganism identified. Once the pathogen is known, the primary line of defense is intensive antimicrobial eye drops. For bacterial infections, antibiotic drops are prescribed; for fungal infections, antifungal drops are used; and for viral infections, antiviral drops are administered. These treatments often require application as frequently as every hour to control the infection.
In some cases, eye drops alone may not be sufficient. An ophthalmologist might also prescribe oral medications to supplement the topical treatment. Infections caused by the Acanthamoeba parasite are notoriously difficult to treat, as the organism can be resistant to medication. This form of keratitis often requires a prolonged treatment course that can last for several months.
If the infection is severe, does not respond to medication, or has caused significant corneal damage, more invasive measures may be required. When extensive scarring leads to substantial vision loss, a corneal transplant (keratoplasty) may be recommended. This surgical procedure replaces the damaged cornea with healthy donor tissue to restore sight.
Prevention and Potential Complications
Preventing microbial keratitis largely centers on mitigating the most common risk factors, especially those related to contact lenses. Proper lens hygiene is paramount. This includes always washing hands before handling lenses, using only sterile solutions for cleaning and storage, and replacing the lens case every three to six months. Adhere to the prescribed wearing schedule and never wear lenses while swimming or sleeping unless specifically approved.
Failure to treat microbial keratitis promptly can lead to serious consequences. The infection can cause permanent scarring of the cornea, which can obstruct or distort vision, sometimes resulting in irreversible vision loss. Other potential complications include glaucoma from changes in eye pressure, perforation of the cornea, or the spread of the infection deeper into the eye (endophthalmitis).