Fungal Keratitis: Causes, Diagnosis and Treatment
What Is Fungal Keratitis
Fungal keratitis is a serious infection of the cornea caused by microscopic fungi that can threaten your eyesight if not identified and treated promptly. The cornea is a transparent dome of tissue that covers the iris and pupil, providing roughly two-thirds of the eye's focusing power and serving as a protective barrier. When the cornea becomes infected, its clarity can diminish, directly affecting the quality of your vision.
Fungi do not typically penetrate an intact, healthy cornea. An infection usually begins when a break in the corneal surface, whether from an injury, a contact lens complication, or a surgical wound, allows fungal organisms to enter the tissue. Once inside, fungi can spread slowly through the layers of the cornea, triggering inflammation and tissue damage. According to the CDC and published studies, fungal keratitis accounts for approximately 5 to 10 percent of infectious keratitis cases in the United States, with higher rates in tropical and subtropical regions.
The most frequently identified organisms include Fusarium species (found in soil and on plants, the leading cause of fungal keratitis in tropical and subtropical regions), Aspergillus species (another filamentous mold commonly associated with outdoor eye injuries involving organic matter), and Candida species (a type of yeast that tends to affect people with pre-existing ocular surface disease or compromised immune systems).
Causes of Fungal Eye Infections
One of the most well-documented causes of fungal keratitis is an eye injury involving vegetation, soil, or other organic matter. Activities such as gardening, farming, trimming branches, or working outdoors in windy conditions can lead to small corneal scratches that introduce fungal spores directly into the tissue. Even a seemingly minor scratch can become a pathway for infection.
Improper contact lens hygiene is another significant risk factor. Sleeping in lenses, rinsing them with tap water, or reusing old solution creates an environment where fungi can colonize the lens surface. Patients should also be aware that organisms like Acanthamoeba can cause similarly serious corneal infections through comparable hygiene failures.
Topical corticosteroid eye drops can suppress the local immune response on the ocular surface, making it easier for fungal organisms to establish an infection. This is particularly concerning when steroid drops are used to treat an eye condition that has not been properly cultured. Systemic immunosuppression from conditions such as diabetes, HIV, or immunosuppressive medications can also increase susceptibility.
Symptoms of Fungal Keratitis
The initial symptoms of fungal keratitis often resemble those of other types of corneal infection. You may notice increasing eye pain, redness, tearing, sensitivity to light, and a sensation that something is stuck in your eye. Blurred vision may develop gradually as the infection spreads.
Certain clinical features can help differentiate a fungal infection from a bacterial one. Fungal keratitis may produce a corneal infiltrate with feathery or irregular borders, satellite lesions (small spots of infection surrounding the main area), and a raised or dry-looking ulcer surface. These characteristics differ from the more well-defined edges typically seen in bacterial keratitis.
Any combination of eye pain, redness, light sensitivity, and worsening vision after an eye injury or during contact lens wear should be evaluated promptly. If your symptoms are not improving with prescribed antibiotic drops, this may be an important clue that a fungal or atypical organism is involved.
How Fungal Keratitis Is Diagnosed
The evaluation begins with a detailed slit-lamp examination, which allows your doctor to view the cornea under high magnification. Special dyes such as fluorescein may be applied to highlight areas of tissue damage. The pattern and depth of the corneal infiltrate often provide the first clues.
To confirm the diagnosis and identify the specific fungus, our cornea specialists perform a corneal scraping. A small sample of tissue is collected from the edges and base of the ulcer and sent for laboratory culture and staining. Cultures may take several days to grow.
Because fungal keratitis can mimic other corneal infections, particularly herpes simplex keratitis, early and accurate identification of the causative organism is critical. Misdiagnosis can lead to inappropriate treatment, delayed recovery, and a greater risk of permanent corneal damage.
Frequently Asked Questions
Fungi grow more slowly than bacteria and can penetrate deeper into the corneal layers, making them harder to reach with topical medications. Many antifungal drugs also have limited ability to pass through intact corneal tissue. Additionally, fungal keratitis is often diagnosed later than bacterial infections.
The primary treatment is intensive topical antifungal eye drops. Natamycin is generally the first-line agent for filamentous fungi like Fusarium and Aspergillus, while amphotericin B is often preferred for yeast infections caused by Candida. In more severe infections, oral antifungal medications such as voriconazole or fluconazole may be added.
Treatment typically lasts several weeks to months, depending on the severity of the infection. Eye drops are often administered as frequently as every hour during the initial phase, then gradually tapered as the infection improves.
Yes, fungal keratitis can cause lasting vision impairment if the infection leads to significant corneal scarring, perforation, or spread to the interior of the eye. Early detection and aggressive treatment offer the best chance of preserving vision. In cases where scarring is substantial, a corneal transplant may eventually be considered.
Protective eyewear during gardening, yard work, and outdoor activities is one of the most effective preventive measures. If you wear contact lenses, always follow recommended cleaning and storage guidelines, replace your lens case regularly, and never expose your lenses to tap water.
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