Candida is a common yeast that naturally inhabits various areas of the human body, including the skin, mouth, and gastrointestinal tract. While usually harmless, an overgrowth or introduction into a sterile environment, such as the eye, can cause a serious infection. When Candida affects the eye, it causes ocular candidiasis, which manifests as either mycotic keratitis (an infection of the cornea) or endophthalmitis (an infection of the inner eye structures). These fungal eye infections are rare compared to bacterial or viral infections, but they represent a medical emergency due to their potential for rapid and permanent vision loss.
Routes of Infection and Primary Risk Factors
The fungus gains access to the eye tissue through two main pathways: exogenous (from an external source) or endogenous (from within the body). The exogenous route typically involves a breach of the eye’s protective surface, such as through trauma or a surgical procedure. An eye injury involving organic matter like a stick or plant debris is a significant risk factor, as environmental fungi can be directly inoculated into the cornea.
Improper contact lens hygiene is another common exogenous factor for the general public, where the yeast can contaminate the lens or storage solution and subsequently infect the corneal surface. Recent eye surgery, such as cataract removal or corneal transplantation, also creates an opportunity for the fungus to enter the eye. In these cases, the infection is often localized to the front of the eye as keratitis.
The endogenous route occurs when a Candida infection elsewhere in the body spreads to the eye through the bloodstream, a process called hematogenous dissemination. This often begins with candidemia, a systemic fungal infection in the blood that can seed the infection in the highly vascular choroid and retina. Individuals with weakened immune systems are at elevated risk for this internal spread, including those with diabetes, prolonged neutropenia, or those receiving high-dose corticosteroids. Other predisposed patients include those with indwelling catheters, those undergoing long-term use of broad-spectrum antibiotics, or intravenous drug users.
Recognizing Clinical Signs and Diagnostic Methods
The clinical signs of a Candida eye infection are often similar to other types of microbial keratitis, but they frequently progress more slowly or show resistance to initial antibiotic treatment. Patients commonly report symptoms like severe and persistent eye pain, redness, blurred vision, and heightened sensitivity to light, known as photophobia. A discharge from the eye and excessive tearing may also occur, though these signs are non-specific.
When the infection is deep within the eye, as with endophthalmitis, a distinctive presentation can include creamy-white, well-circumscribed lesions in the retina and vitreous, sometimes described as having a “string of pearls” appearance. Because the symptoms can mimic other conditions, a prompt and accurate diagnosis is required to prevent severe vision loss. The ophthalmologist begins with a thorough examination using a slit-lamp microscope to assess the cornea and the internal structures.
A definitive diagnosis relies on obtaining a sample of infected tissue or fluid, which is typically done via corneal scraping or, for deeper infections, a vitreous or aqueous humor biopsy. This sample is then sent to a laboratory for direct microscopic examination and culturing to confirm the presence of Candida and determine its specific species. Newer diagnostic techniques, such as Polymerase Chain Reaction (PCR) testing, can also be used to quickly detect the fungal DNA, providing a rapid result for initiating appropriate therapy.
Standard Medical and Surgical Treatment Strategies
Treatment for a Candida eye infection is often prolonged due to the challenging penetration of antifungal medications into the eye. For infections limited to the corneal surface (keratitis), the first line of defense involves intensive application of topical antifungal agents. Medications like amphotericin B drops are often the drug of choice, as they are effective against Candida species.
When the infection has spread deeper into the cornea or involves the internal eye (endophthalmitis), systemic antifungal therapy is essential, often administered both orally and intravenously. Voriconazole and fluconazole are commonly used systemic drugs that achieve good concentrations in the vitreous humor to eradicate the internal infection. The course of medical treatment typically lasts for several weeks to months, requiring consistent follow-up to ensure the infection is completely cleared.
If the infection fails to respond to drug therapy, or if the eye structure is severely compromised, surgical intervention becomes necessary. A vitrectomy, which involves surgically removing the infected vitreous gel from the eye, may be performed to reduce the fungal load and allow better penetration of antifungal drugs. In cases of severe corneal damage or perforation, a therapeutic penetrating keratoplasty, a type of corneal transplant, may be required to control the infection and preserve the integrity of the eye.
Prevention for High-Risk Groups
Preventing Candida eye infections focuses on minimizing the risk factors that allow the fungus to enter or spread to the eye. For the general population, maintaining strict contact lens hygiene is crucial, including cleaning lenses with fresh solution daily and never sleeping in lenses not approved for overnight wear.
Contact lens wearers should also clean their storage cases regularly and replace them as recommended to prevent biofilm formation by the yeast. Individuals whose work involves exposure to outdoor environments, such as agricultural workers, should always wear appropriate protective eyewear to prevent eye trauma from organic matter.
Any eye injury, particularly one involving plant material, should be examined by a healthcare provider immediately to flush out debris and assess for potential fungal inoculation. For patients with underlying health conditions, such as those with a history of candidemia, diabetes, or immune suppression, careful management of their systemic disease is important to reduce the overall risk of endogenous eye infection.