Introduction:
Fungal keratitis, a fungal infection of the cornea, is potentially a major cause of ocular morbidity in developing countries. It causes inflammation and destruction of corneal structures, which leads to blindness. It causes corneal lesions and changes in vision. Fungal keratitis is difficult to diagnose and treat.
What Is Fungal Keratitis?
Fungal keratitis, also called a fungal corneal ulcer, is an infection of the cornea caused by fungus. It includes Fusarium species, Aspergillus species, and Candida species.
What Are the Signs and Symptoms?
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Corneal lesions.
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Satellite lesions with hypopyon satellite lesions - the presence of smaller lesions near the edge of the principal lesion. hypopyon-accumulation of neutrophils and fibrins in the anterior chamber.
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Eye pain.
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Blurred vision.
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Excessive tearing.
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Light sensitivity.
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Eye discharge.
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Foreign body sensation.
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Corneal tearing.
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Purulent secretions from the eye.
What Are the Sources of Fungi?
Fusarium and Aspergillus species are found in the environment. Candida species normally live on human skin, the lining of the eyes, nose, and mouth.
What Are the Risk Factors for Fungal Keratitis?
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Weak immune system.
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Persistent eye disease
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Contact lens use.
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Eye trauma.
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Topical steroid use.
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Ocular surface disease.
How Does the Infection Occur?
The infection begins when there is a break in the epithelium, the integrity of the epithelium is lost, and the organism has access to the eye and starts proliferation. The organisms release various antigens, toxins, and enzymes that cause necrosis and damage. This causes alterations in the functioning of the eye.
How to Diagnose Fungal Keratitis?
Clinical Diagnosis:
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The diagnosis is made based on the characteristic clinical features. The presenting complaints of the patients will be sudden pain, watering, discharge from the eye, photophobia, and reduced vision.
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The classic sign of fungal keratitis is dry, raised lesions with feathery borders and the presence of satellite lesions and a hypopyon.
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Immune ring of Wesseley- deposition of immune complexes and inflammatory cells around the ulcer.
Confocal Microscopy:
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Noninvasive technique for the diagnosis of fungal keratitis.
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Produces images of the cornea with a resolution of one micrometer, which enables one to see microorganisms larger than one micrometer.
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Rapid and reliable diagnostic tool.
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In vivo, confocal microscopy, or IVCM helps to see the whole cornea with the presence of filamentous fungi.
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Rapid identification and differentiation of fungal species.
Laboratory Diagnosis:
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Conventional method.
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Corneal tissue is scraped off, and staining is done.
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Gram staining with 10 % potassium hydroxide wet mount, lactophenol cotton blue, and Giemsa stain are used.
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The most commonly used method to detect fungi.
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A rapid and inexpensive diagnostic method
Polymerase Chain Reaction (PCR):
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PCR involves repeated cycles of denaturation, amplification, and amplification of DNA segments.
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Specific and sensitive test for fungal keratitis.
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Higher positivity rate when compared to other techniques.
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The rapid test takes four to eight hours.
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A small clinical sample is required for PCR.
Metagenomic Deep Sequencing:
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A new technique for the diagnosis of fungal keratitis.
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A more accurate diagnosis is possible.
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Helps identify all the microorganisms involved.
How Fungal Keratitis Is Treated?
Topical antifungals or eye drops are the first line of treatment. Fungal keratitis is treated with topical or systemic antifungal medicines or in combination with surgical treatment. Following are the antifungal drugs.
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Polyenes:
- Amphotericin B.
- Natamycin.
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Azoles:
- Fluconazole.
- Itraconazole.
- Ketoconazole.
- Miconazole.
- Voriconazole.
- Posaconazole.
- Pyrimidines.
- Flucytosine.
What Is the Surgical Treatment for Fungal Keratitis?
When fungal keratitis does not respond to medical treatment, surgical treatment is considered.
1. Penetrating Keratoplasty:
Treatment for severe fungal keratitis. In this procedure, the damaged cornea or a part of the cornea is surgically removed and replaced with healthy corneal tissue from a donor. This procedure is also called a corneal transplant or corneal graft.
2. Intrastromal Voriconazol:
This procedure works on the principle of targeted drug delivery, where the deep fungal keratitis is not responding to standard topical therapy. It helps in the delivery of the drug close to the lesion or infected area. The drug is introduced by intrastromal injections.
3. Intracameral Amphotericin B:
It is also a targeted drug delivery system. This method is used when systemic and topical antifungal therapy has failed. Usually performed in cases with an endothelial plaque and with the presence of hypopyon associated with inflammation of the anterior chamber of the eye. The concentration of the drug ranges from 5 and 10 μg/0.1 ml.
4. Amniotic Membrane Transplantation:
This surgical procedure has emerged to prevent fungal keratitis secondary to penetrating Keratoplasty. The amniotic membrane helps in ocular surface reconstruction and re-epithelialization of the tissue. This procedure helps to prevent pain.
In patients undergoing penetrating Keratoplasty, there is a risk of graft rejection, which can increase the chance of fungal infections. To avoid such complications, the penetrating keratoplasty has to be delayed.
5. Lamellar Keratoplasty:
An alternate surgical procedure where only the affected or diseased layers of the corneal surface are removed and replaced with donor corneal tissue.
6. Corneal Collagen Cross-Linking (CXL):
CXL is a successful procedure that halts the progression of keratoconus by using riboflavin and UV-A light. In fungal keratitis, it provides a direct antifungal effect and stops the ongoing spreading. This also helps to avoid emergency Keratoplasty.
7. Rose Bengal Photodynamic Therapy:
This technique uses a photochemical process using Rose bengal, and generates reactive oxygen species. The technique was found useful in patients who were unresponsive to standard medical therapy. In fungal keratitis, the infection is controlled without leading to penetrating keratoplasty.
How to Prevent Fungal Keratitis?
It is prevented by using protective eyewear while doing tasks that could harm the eyes while working in agricultural fields. Also look for symptoms such as red eyes, pain, and discomfort and contact the doctor. Contact lens hygiene is to be maintained for the prevention of fungal keratitis.
Conclusion:
Early diagnosis and treatment for fungal keratitis is a bit challenging. Understanding pathogenesis is important in the management of disease. Recent advances have provided more efficient treatment options. Newer antifungals and targeted drug delivery systems helped improve the outcome. Most studies are being carried out to modify the immune response to the infection, which could stop the spread of infection and improve visual outcomes.
