Fungal Infections in Eye: Causes, Symptoms, Diagnosis & Treatment

Fungal infections of the eye are among the most underdiagnosed — and most dangerous — ocular conditions a clinician encounters or a patient can experience. Unlike bacterial infections, which respond quickly to standard antibiotic treatment, fungal eye infections are slow to develop, difficult to identify, and require specific antifungal therapy to resolve.

Left untreated or misidentified, fungal keratitis — the most common form of fungal eye infection — can progress to permanent corneal scarring, vision loss, and in severe cases, the need for a corneal transplant. Understanding this condition in depth is not just clinically important; it is sight-saving.

This guide covers everything you need to know: what causes fungal eye infections, how to recognise them, how they are diagnosed and treated, and — critically — how they can be prevented.

What Are Fungal Eye Infections?

A fungal eye infection occurs when a fungal organism invades one or more structures of the eye. The most common target is the cornea — the clear, dome-shaped front surface of the eye — resulting in a condition known as fungal keratitis or keratomycosis. Less commonly, fungi can invade deeper ocular structures, causing conditions such as fungal endophthalmitis, an infection of the interior of the eye that carries an even graver prognosis.

Unlike bacterial or viral infections, fungal eye infections are not caused by a single organism. Over 70 fungal species have been implicated in ocular infections, though the most clinically significant fall into two broad categories: filamentous fungi and yeasts.

Types of Fungal Eye Infections

Fungal Keratitis (Keratomycosis)

Fungal keratitis is an infection of the cornea caused by fungal organisms. It is the most common form of fungal eye infection and is responsible for a significant proportion of infectious corneal blindness worldwide — particularly in tropical and subtropical regions where agricultural trauma is prevalent.

It is characterised by corneal ulceration, which can progress rapidly if not treated promptly. The infection can penetrate deeply into corneal stroma, making it difficult to eradicate with topical treatment alone.

Filamentous Fungal Keratitis

Caused by mould species such as Fusarium, Aspergillus, and Curvularia, filamentous fungal keratitis is the most common type globally. It is strongly associated with ocular trauma involving plant material — a thorn scratch, a grain of rice, or a branch to the eye can introduce these organisms directly into the corneal tissue.

Filamentous fungi grow as branching, thread-like structures called hyphae that can spread across corneal layers rapidly, making the infection particularly aggressive and difficult to treat.

Yeast Keratitis

Caused by species such as Candida albicans and other Candida species, yeast keratitis presents differently from filamentous infections. It tends to occur in immunocompromised patients, those with pre-existing ocular surface disease (such as dry eye or chronic keratitis), or patients on long-term topical corticosteroids.

Candida keratitis typically progresses more slowly than filamentous disease and may have a somewhat different clinical appearance, often presenting with a more discrete, creamy-white infiltrate.

Fungal Endophthalmitis

Fungal endophthalmitis is an infection of the vitreous cavity and internal structures of the eye. It can arise in two ways: as an extension of severe fungal keratitis that has perforated the cornea, or — more commonly in developed countries — through haematogenous spread in patients with systemic fungal infections, particularly those with Candida bloodstream infections (candidaemia).

Patients at highest risk include those in intensive care, recipients of prolonged intravenous lines, solid organ transplant recipients, and patients receiving immunosuppressive therapy. Fungal endophthalmitis carries a poor visual prognosis and requires aggressive systemic and, often, intravitreal antifungal therapy.

Causes and Risk Factors

Understanding who is at risk — and why — is fundamental to both prevention and early suspicion of fungal eye infection. The risk factors differ somewhat depending on whether the infection is filamentous or yeast-based.

Common Causes

• Ocular trauma, particularly with plant or agricultural material: Accounts for the majority of filamentous fungal keratitis cases globally. Farmers, gardeners, and agricultural workers are disproportionately affected.
• Contact lens wear: Extended wear, poor hygiene, using tap water to rinse lenses or cases, and wearing lenses during swimming or showering all significantly increase risk.
• Previous ocular surgery: Any surgery that disrupts the corneal epithelium — including LASIK and corneal transplantation — creates a potential entry point for fungal organisms.
• Long-term topical corticosteroid use: Corticosteroids suppress local immune defences and can promote fungal proliferation. This is also why misdiagnosed fungal keratitis treated with steroids rapidly worsens.
• Systemic immunosuppression: HIV/AIDS, diabetes mellitus, haematological malignancies, and immunosuppressive medications all reduce the body’s capacity to contain fungal organisms.
• Chronic ocular surface disease: Conditions such as severe dry eye, bullous keratopathy, and neurotrophic keratitis compromise the corneal epithelial barrier.

Geographic and Environmental Factors

The epidemiology of fungal keratitis varies significantly by geography. In tropical and subtropical regions (South Asia, Sub-Saharan Africa, Latin America), filamentous fungi — particularly Fusarium — dominate. In temperate, developed countries, Candida species are proportionally more prevalent, especially in urban hospital settings.

Seasonal variation also plays a role — fungal keratitis incidence rises during harvest seasons in agricultural communities, consistent with the association between plant trauma and filamentous infection.

Symptoms: What to Look For

The symptoms of fungal keratitis overlap with other forms of infectious keratitis, which is one of the reasons it is so frequently misdiagnosed. However, certain features — particularly the clinical context and the time course — can raise suspicion.

Symptoms in the Patient

• Eye pain — often described as a deep, aching discomfort, which may be disproportionate to visible signs
• Redness — diffuse or localised conjunctival injection
• Photophobia — sensitivity to light, often significant
• Excessive tearing or watering of the eye
• Blurred or reduced vision
• Sensation of a foreign body within the eye
• Discharge — typically less purulent than in bacterial keratitis
• Eyelid swelling in moderate-to-severe cases

Distinguishing Fungal from Bacterial and Viral Keratitis

While definitive differentiation requires laboratory investigation, the following clinical features can aid initial suspicion:

Diagnosis: How Fungal Eye Infections Are Identified

Accurate diagnosis of fungal keratitis requires a combination of clinical assessment and laboratory investigation. The diagnosis should be suspected clinically and confirmed microbiologically — empirical antifungal treatment while awaiting results is often appropriate in high-risk presentations.

Clinical Examination

A thorough slit-lamp examination is the cornerstone of clinical assessment. Slit-lamp biomicroscopy allows the clinician to assess the size, depth, and characteristics of any corneal infiltrate or ulcer. Specific features that raise the probability of fungal aetiology include a feathery or irregular infiltrate border, satellite lesions, immune rings, and an endothelial plaque.

The depth of stromal involvement is also an important prognostic indicator — deep infiltrates that approach or involve Descemet’s membrane carry a high risk of perforation and a poor visual prognosis.

Microbiological Investigation

• Corneal scraping: The gold standard for diagnosis. Samples are taken from the leading edge of the ulcer and sent for microscopy, culture, and sensitivity. Multiple scraping techniques may be used — spatula, Kimura spatula, or surgical blade.
• Microscopy with stains: Gram stain, Giemsa stain, potassium hydroxide (KOH) preparation, and calcofluor white staining can identify fungal elements (hyphae or yeast cells) directly. KOH preparation with calcofluor white fluorescence is particularly sensitive for rapid fungal identification.
• Culture: Samples are plated on Sabouraud dextrose agar and other fungal media. Culture remains the definitive method for species identification and antifungal sensitivity testing, though results take 1–3 weeks.
• PCR (Polymerase Chain Reaction): Increasingly available in specialist centres. PCR can identify fungal DNA within hours from corneal scrapings, offering much faster species identification than culture.

Advanced Imaging

In vivo confocal microscopy (IVCM) of the cornea has emerged as a valuable non-invasive adjunct in the diagnosis of fungal keratitis. This technology enables real-time imaging of corneal layers at cellular resolution, allowing direct visualisation of fungal hyphae within corneal stroma without requiring a scraping.

Treatment: What Works and What Doesn’t

Fungal keratitis is notoriously difficult to treat. The cornea has limited vascularity, which restricts drug penetration, and many antifungal agents have poor corneal bioavailability. Treatment is typically prolonged — often weeks to months — and requires close monitoring for response and complications.

Topical Antifungal Therapy

Topical antifungal eye drops are the first line of treatment for fungal keratitis. The choice of agent depends on the suspected or confirmed organism:

• Natamycin 5% ophthalmic suspension: The only commercially available topical antifungal specifically formulated for ophthalmic use. It is the treatment of choice for filamentous fungi, particularly Fusarium. It works by binding to ergosterol in the fungal cell membrane, disrupting membrane integrity.
• Voriconazole 1% eye drops: A broad-spectrum azole antifungal with excellent activity against both filamentous fungi and Candida. Increasingly used as first-line or adjunctive therapy, particularly for Aspergillus and deep keratitis. Available as compounded eye drops in most settings.
• Fluconazole 0.3% eye drops: Primarily used for Candida keratitis. Less effective against filamentous fungi.
• Amphotericin B 0.15% eye drops: A broad-spectrum agent with activity against many filamentous fungi and yeasts. Often used in combination regimens or when first-line agents have failed.

In severe cases, drops may initially be prescribed hourly during waking hours, with gradual tapering as the infection responds. Total treatment duration is typically 6–12 weeks, though some cases require longer therapy.

Systemic Antifungal Therapy

Oral or intravenous antifungal agents are used as adjuncts to topical therapy in severe keratitis, when there is scleral involvement, or in cases of fungal endophthalmitis. Voriconazole has excellent oral bioavailability and good ocular penetration, making it the preferred systemic agent for filamentous infections. Fluconazole is preferred for systemic Candida infections.

Intrastromal and Intracameral Injection

In cases of deep stromal keratitis not responding to topical therapy, direct injection of antifungal agents into the corneal stroma (intrastromal injection) or anterior chamber (intracameral injection) can achieve drug concentrations far exceeding those attainable topically. Voriconazole is the most commonly used agent for this approach.

Surgical Intervention

When medical therapy fails to control the infection, surgical options may be required:

• Corneal debridement: Removal of infected epithelium to enhance drug penetration. Often performed at the time of diagnostic scraping.
• Therapeutic penetrating keratoplasty (TPK): Emergency corneal transplantation performed not to restore vision, but to remove the infected tissue and prevent perforation or intraocular spread. TPK carries significant risks in an actively infected eye and has variable outcomes.
• Conjunctival flap: In select cases, covering the ulcer with a conjunctival flap can provide vascular support to the avascular cornea, improving drug delivery and tectonic stability.
• Evisceration or enucleation: In end-stage cases with complete visual loss and uncontrollable infection, removal of the eye contents or the entire globe may be necessary to prevent spread and relieve pain.

Prevention: Reducing Your Risk

Many cases of fungal keratitis are preventable. The strategies below are relevant both for individual patients and for clinical settings advising at-risk populations.

For All Patients

• Wear protective eyewear during gardening, agricultural work, woodworking, and any activity involving plant or vegetative material
• Seek immediate medical attention after any eye injury involving plant material — do not wait for symptoms to develop
• Avoid touching or rubbing your eyes with unwashed hands
• Do not self-medicate with over-the-counter antibiotic eye drops for eye pain or redness — this delays diagnosis and the use of steroids for presumed inflammation can worsen a fungal infection

For Contact Lens Wearers

• Always wash hands thoroughly before handling lenses
• Never rinse lenses or storage cases with tap water, saliva, or any solution other than sterile contact lens solution
• Replace lens cases monthly and allow them to air dry between uses
• Remove lenses before swimming, showering, or using hot tubs
• Follow the replacement schedule for your lenses — never overwear
• Remove lenses immediately if you experience any pain, redness, or blurred vision and consult an eye care professional

For Clinicians and Practice Managers

• Maintain a high index of suspicion for fungal keratitis in patients presenting with corneal ulcers following ocular trauma, particularly in agricultural contexts
• Perform corneal scraping and microbiological investigation early — do not delay for the sake of a treatment trial
• Ensure diagnostic equipment — particularly slit lamps — is properly maintained and calibrated for reliable clinical assessment
• Educate patients in at-risk occupations about protective eyewear and the importance of early presentation after eye injury

The Role of Ophthalmic Equipment in Diagnosis and Monitoring

The quality of ophthalmic equipment directly affects the quality of clinical decisions made in cases of fungal keratitis. This is not a minor point — in a condition where the margin between a good and poor outcome can be days, having reliable, well-maintained diagnostic tools is clinically significant.

Essential Equipment for Fungal Keratitis Management

• Slit-lamp biomicroscope: Every detail matters in corneal examination — infiltrate borders, depth, satellite lesions, endothelial involvement, and anterior chamber reaction. A slit lamp with poor optics or inadequate illumination limits the clinician’s ability to make these assessments accurately.
• Corneal topographer: Provides a detailed map of corneal curvature and can help track changes in corneal shape and regularity as an indirect measure of disease progression or resolution.
• Anterior segment OCT: Enables precise measurement of infiltrate depth within the corneal stroma — critical for surgical planning and assessing proximity to Descemet’s membrane.
• In vivo confocal microscope: Allows direct non-invasive visualisation of hyphal elements within the cornea, supporting rapid clinical diagnosis without requiring a scraping in some cases.
• Fundus camera and posterior segment OCT: Essential in cases where fungal endophthalmitis is suspected — allows assessment of vitreous clarity, retinal involvement, and posterior segment complications.

When to Seek Urgent Care

Fungal keratitis is a medical emergency. If you or a patient experiences any of the following, same-day ophthalmological assessment is essential — do not wait and see:

Early intervention is the single most important determinant of outcome in fungal keratitis. Patients who present within the first week of symptoms have significantly better visual outcomes than those who delay. The eye care professional’s ability to act quickly — and to have the diagnostic tools to do so — makes all the difference.

Frequently Asked Questions

Q: Can a fungal eye infection go away on its own?

A: No. Fungal eye infections do not resolve without treatment. Unlike minor bacterial conjunctivitis, which can sometimes self-resolve, fungal keratitis will progress without appropriate antifungal therapy. Early treatment is critical — delays worsen outcomes significantly.

Q: How long does treatment for fungal keratitis take?

A: Treatment is prolonged compared to bacterial infections. Most cases require 6–12 weeks of topical antifungal therapy, and some severe cases require longer. Patients should not stop treatment when symptoms improve — premature cessation is a common cause of relapse.

Q: Are antifungal eye drops available over the counter?

A: No. Antifungal eye drops such as natamycin and voriconazole are prescription-only medications. Over-the-counter eye drops — particularly those containing antibiotics or steroids — are not appropriate for fungal keratitis and can worsen the condition.

Q: Can contact lenses cause fungal eye infections?

A: Yes. Contact lens wear is one of the significant risk factors for fungal keratitis, particularly when lenses are worn in water (swimming, showering), stored improperly, or worn beyond their recommended schedule. Proper lens hygiene dramatically reduces this risk.

Q: What is the difference between fungal keratitis and bacterial keratitis?

A: Both are infections of the cornea, but they are caused by different organisms and require different treatments. Bacterial keratitis responds to antibiotic eye drops; fungal keratitis requires specific antifungal agents. Fungal keratitis typically progresses more slowly, is associated with plant trauma or contact lens use, and is more difficult to treat. Misidentification of fungal keratitis as bacterial — and the subsequent use of antibiotics (and potentially steroids) — is a major cause of poor outcomes.

Q: Can fungal keratitis cause blindness?

A: Yes, in severe or inadequately treated cases. Fungal keratitis can lead to corneal perforation, scarring, and permanent vision loss. However, with early diagnosis and appropriate treatment, many patients retain good vision. This is why prompt presentation and accurate diagnosis are so critical.

Q: Is fungal endophthalmitis different from fungal keratitis?

A: Yes. Fungal keratitis involves the cornea — the front surface of the eye. Fungal endophthalmitis involves the interior of the eye (vitreous, retina, choroid) and carries a more serious prognosis. Endophthalmitis can develop as a complication of untreated keratitis, or arise independently through the bloodstream in systemically unwell patients.

Conclusion

Fungal infections of the eye represent a serious, sight-threatening group of conditions that demand clinical vigilance, accurate diagnosis, and timely targeted treatment. Fungal keratitis in particular is a condition where delays — whether in presentation, diagnosis, or the initiation of correct therapy — carry a disproportionate cost to the patient’s vision.

The fundamentals are clear: know the risk factors, recognise the symptoms, investigate early with the right tools, treat promptly with appropriate antifungal agents, and never apply steroids to an eye with an undiagnosed corneal ulcer. For patients in at-risk occupations or with contact lens habits, prevention through protective eyewear and good hygiene practice is entirely achievable.

For eye care professionals, having reliable, well-maintained diagnostic equipment is not a secondary concern — it is central to the quality of care that can be delivered. Every examination that leads to an earlier diagnosis, every corneal image that guides a surgical decision, depends on the quality of the instruments in use.