Microsporidial keratitis is an infrequent infection of the cornea, the transparent front layer of the eye. This condition is caused by a group of parasites known as microsporidia. While once considered rare, it is increasingly recognized as a cause of corneal inflammation. The infection can lead to a range of symptoms and requires specific diagnostic procedures to distinguish it from other eye conditions.
Understanding Microsporidia and Corneal Infection
Microsporidia are spore-forming, single-celled parasites classified as fungi or closely related organisms. As obligate intracellular parasites, they can only reproduce inside a host’s cells. Spores from these organisms are widespread in the environment, found in soil and water. Infection occurs when these spores directly contact the eye, penetrating the cornea’s cellular layers and multiplying.
Several factors increase the risk of this infection. Eye trauma involving soil, mud, or contaminated water can introduce spores to the corneal surface. Contact lens wear combined with poor hygiene, such as using tap water for rinsing or storage, is another risk factor. Individuals with compromised immune systems were historically the most affected, but the infection is now more frequently reported in people with healthy immune systems.
The infection can manifest differently depending on which corneal layers are affected. It can present as keratoconjunctivitis, an inflammation of both the cornea and the conjunctiva. In other cases, it may cause a deeper inflammation within the main structural layer of the cornea, referred to as stromal keratitis.
Recognizing the Signs of Infection
The symptoms of microsporidial keratitis can develop gradually and often resemble those of other common eye infections, making self-diagnosis difficult. A primary symptom is often a persistent feeling that something is in the eye, known as a foreign body sensation. This is frequently accompanied by eye pain, which can range from mild irritation to more significant discomfort, and noticeable redness of the eye.
Visual disturbances are also a common characteristic of the infection. Patients may experience blurred vision, which can worsen as the infection progresses. Another frequent complaint is photophobia, an increased sensitivity to light that can make being in bright environments uncomfortable. The eye may also produce excessive tears or a watery discharge as it attempts to respond to the infection.
In some presentations, the clinical signs can be quite specific. An ophthalmologist might observe grayish-white lesions on the surface of the cornea during an examination. The infection can also cause a pattern of small dots on the cornea, a condition called superficial punctate keratitis.
Diagnostic Procedures for Microsporidial Keratitis
Confirming a diagnosis of microsporidial keratitis involves a patient history, a detailed eye examination, and laboratory tests. During the examination, an eye doctor will use a slit-lamp microscope for a highly magnified view of the cornea, looking for characteristic signs of the infection.
To definitively identify the parasite, a procedure called corneal scraping is performed to collect a small sample of cells from the cornea’s surface. The sample is sent to a laboratory where special stains, like Giemsa or calcofluor white, are used to make the microsporidial spores visible under a microscope for confirmation.
If the infection is suspected to be deeper within the corneal tissue (stromal keratitis), surface scrapings may not be sufficient. In these situations, in vivo confocal microscopy (IVCM) allows an ophthalmologist to view the corneal layers at a cellular level in real-time. This can reveal the highly reflective microsporidia spores without a physical sample. For precise species identification, molecular methods like polymerase chain reaction (PCR) can be used to amplify the parasite’s DNA from a corneal sample.
Therapeutic Approaches to Treatment
The treatment for microsporidial keratitis is tailored to the infection’s depth and severity. For infections confined to the superficial epithelial layer of the cornea, medical therapies are employed. This often begins with debridement, the mechanical removal of infected cells to reduce the number of parasites on the eye’s surface.
Following debridement, topical antimicrobial medications are prescribed. Antifungal eye drops containing voriconazole or antiseptic agents like chlorhexidine are used to eliminate the remaining organisms. In some cases, topical fumagillin, an antimicrobial agent effective against microsporidia, may be compounded for use, though its availability can be limited.
When the infection penetrates into the deeper stromal layer of the cornea, treatment becomes more challenging and may require a combination of topical and oral medications. Oral antifungal drugs like albendazole might be added to the treatment plan to help fight the infection systemically. In severe cases that do not respond to medication or where significant scarring has occurred, a surgical procedure such as a corneal transplant (keratoplasty) may be necessary to remove the infected tissue and restore vision.
Outlook and Prevention Strategies
With timely diagnosis and appropriate treatment, the outlook for microsporidial keratitis is positive. Most cases affecting only the corneal surface resolve with medication, leading to a full recovery of vision. Delays in diagnosis or treatment can lead to complications. Deep stromal infections are more difficult to manage and can result in corneal scarring, which may cause permanent vision impairment.
Prevention involves minimizing exposure to parasites and practicing good eye hygiene. Contact lens wearers should wash hands thoroughly before handling lenses and never use tap water or non-sterile solutions for cleaning or storage. Following the recommended schedule for lens replacement is also important. Additionally, wearing protective eyewear during activities like gardening or construction can prevent eye injuries involving contaminated soil or water.