What Is Fungal Keratitis?

Fungal keratitis is an infectious keratopathy caused by pathogenic fungi with a high blinding rate. Fungal keratitis has a slow onset and a long course of disease, which can last up to 2 to 3 months. Corneal ulcers often occur within a few days of onset. In China, the majority of peasant patients.

Basic Information

English name

fungal keratitis

Visiting department

Ophthalmology

Multiple groups

Farmer

Common symptoms

Corneal infiltrates are white or gray, visually impaired

Causes of fungal keratitis

Fungal keratitis is an infectious keratopathy caused by pathogenic fungi with a high blinding rate. More than 70 species of fungi have been found to cause corneal infections. According to the different pathogenic effects of fungi in eye infections, they are divided into two categories, filamentous bacteria and yeasts.

Common pathogenic fungi

For Fusarium and Aspergillus. Others include Candida, Penicillium and Yeast.

2. History of plant trauma to the eye

Common stab wounds to branches, sugarcane leaves, straw, etc.

3. Decreased local resistance

Such as contact lens abrasions or corneal surgery, pathogenic fungi can invade the cornea, because 3% to 28% of healthy people can also isolate these fungi in the conjunctival sac.

4. The body's immune dysfunction

Related to the onset of some species. Such as systemic or local long-term use of broad-spectrum antibiotics, glucocorticoids or immunosuppressants.

Clinical manifestations of fungal keratitis

Slow onset, subacute passage, mild irritation, and visual impairment. The corneal infiltrates are white or gray, dense, dry and lackluster in appearance, showing a toothpaste-like or mossy-like appearance. The surface is formed by mycelia and necrotic tissue with a well-defined gray-white raised lesion (mycelium coat). Pseudofoot or satellite-like infiltrates can be seen next to the lesion. Around the ulcer there is a shallow groove formed by the dissolution of collagen or an immune loop formed by the reaction of antigens and antibodies. The body reacts to the antigens and antibodies of the fungus. spot). Anterior chamber pus, grayish white, sticky or pasty. Fungi are highly penetrating, and can easily cause fungal endophthalmitis when entering the anterior chamber or corneal puncture.

Fungal keratitis test

1. Laboratory examination finds fungus and mycelium can be confirmed. Smear examination is an effective method for early and rapid diagnosis of fungal infection. As the disease progresses, repeated scraping of different parts can increase the positive rate.

2. Common methods are corneal scraping Gram and Giemsa staining. Potassium hydroxide can dissolve non-fungal impurities and show fungal hyphae. If 10% to 20% potassium hydroxide wet scraping and culture are negative, the clinical level is high. If in doubt, consider corneal tissue biopsy. A positive corneal scrape or a tissue culture test is the most reliable basis for diagnosing a fungal infection, and it can also identify the fungal species.

3. In addition, immunofluorescence staining, electron microscopy and PCR are also used for the diagnosis of fungal keratitis. The corneal confocal microscope is a non-invasive examination that can directly detect the fungal pathogens in the lesion.

Diagnosis of fungal keratitis

According to the history of corneal plant injury, symptoms usually occur 24 to 36 hours after injury, non-specific changes occur 3 to 4 days, and typical symptoms 4 to 6 days, combined with the characteristics of corneal lesions, can make a preliminary diagnosis.

Mycotic Keratitis Treatment

1. Topical use of antifungal drugs, such as polyenes (pimamycin, amphotericin B), azoles (fluconazole), pyrimidines. Generally, drug treatment can be started based on clinical characteristics and corneal scraping results confirmed as a fungal infection, and medication should be further adjusted based on the results of fungal culture. After the infection is obviously controlled, the number of use can be gradually reduced. If the disease is severe, other methods of administration can be added. It can be injected under the conjunctiva, or the system can be administered intravenously with antifungal drugs. At the same time, carefully observe the clinical characteristics and evaluate the efficacy. The signs of drug action include pain reduction, reduced invasion range, disappearance of satellite foci, and rounded edges of ulcers.

During the treatment, pay attention to the ocular surface toxicity of the drug, including conjunctival congestion, edema, punctate epithelial shedding, etc. The drug treatment should last at least 6 weeks after the effect.

2. For patients with iridocyclitis, atropine eye drops or eye ointment should be used to dilate pupils, and glucocorticoid should not be used. Even if the diagnosis is clear and the medication is timely, some patients cannot be controlled, which may be strongly related to the invasiveness, toxicity, drug resistance of the pathogenic fungus, and the inflammatory response associated with the patient. At this time, surgical treatment should be considered, including debridement and conjunctiva Flap occlusion and corneal transplantation.

3. In principle, those who have not reached the posterior elastic layer should first consider lamellar corneal transplantation. Generally, the following four situations are used to judge the elastic layer before and during the infection without penetration: The slit lamp microscope does not infiltrate the posterior elastic layer; there is no endothelial plaque; There were no obvious lesions and endothelial plaques when peeled to the adjacent posterior elastic layer during the operation. Once the drug treatment fails and the infection reaches the full thickness, the corneal infection perforates, and the corneal lamellar transplant relapses, a penetrating corneal transplant is performed.