FUNGAL KERATITIS

By:Sina MotallebiM.Optom(2nd Sem)Amity Medical School

A fungus is any member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds,as well as the more familiar mushrooms.

Many species produce bioactive compounds called mycotoxins, such as alkaloids and polyketides, that are toxic to animals including humans.

Fusarium Candida albicans

Fungal Keratitis is caused when Fungi gain access into the corneal stroma through a defect in the epithelium, then multiply and cause tissue necrosis and an inflammatory reaction.

Causes

It is caused due to Aspergillus,Fusariumand Candida albicans fungus.Morecommonly by Apergillus.

Its often seen after injury with vegetable matter such as a thorn or a wooden stick.

Risk factors Trauma (eg, contact lenses, foreign

body).

Topical corticosteroid use.

Corneal surgery such as penetrating keratoplasty, clear cornea (sutureless) cataract surgery, photorefractive keratectomy, or laser in situ keratomileusis (LASIK)

Previous history of trauma (vegetable matter).

Agricultural occupations.

Workup

Laboratory:

Corneal scrapings are obtained using a platinum spatula, surgical blade, or calcium alginate swab inoculated on Sabouraud agar plates, and then maintained at 25°C to enhance fungal growth.

Symptoms

Foreign body sensation.

Increasing eye pain or discomfort.

Sudden blurry vision.

Unusual redness of the eye.

Excessive tearing and discharge from the eye.

Increased light sensitivity.

Signs

Conjunctival injection.

Epithelial defect.

Stromal infiltration.

Suppuration

Hypopyon

Presenting clinical features:

Fine or coarse granular infiltrate within the epithelium and anterior stroma.

Gray-white color, dry, and rough corneal surface that may appear elevated.

Typical irregular feathery-edged infiltrate.

White ring in the cornea and satellite lesions near the edge of the primary focus of the infection.

Ophthalmic imaging:

If clinical evidence or suspicion of posterior segment involvement exists, ophthalmic B-scan ultrasound may be necessary to rule out concurrent fungal endophthalmitis.

Other tests:

Immunofluorescence staining.

Electron microscopy.

Confocal microscopy- It may help in correctly

diagnosing early stages of fungal keratitis and in monitoring disease progress at the edges and depth.

Treatment

Medical care:Antifungal agents are classified into the following groups:

Polyenes include natamycin, nystatin, and amphotericin B. Polyenes disrupt the cell by binding to fungal cell wall.

Amphotericin B is the drug of choice for treatment of fungal keratitis caused by Candida.

Natamycin is the only commercially available topical ophthalmic antifungal preparation. It is effective against filamentous fungi, particularly for infections caused by Fusarium.

However, because of poor ocular penetration, it has primarily been useful in cases with superficial corneal infection.

Azoles (imidazoles and triazoles) include ketoconazole, miconazole, fluconazole, itraconazole, econazole, and clotrimazole.

Azoles inhibit ergosterol synthesis at low concentrations, and, at higher concentrations, they appear to cause direct damage to cell walls.

Biomicroscopic signs to assess he efficacy of the medications being used:

Blunting of the perimeters of the infiltrate.

Reduction of the density of the suppuration.

Reduction in cellular infiltrate and edema in the surrounding stroma.

Reduction in anterior chamber inflammation.

Progressive reepithelization.

Loss of the feathery perimeter of the stromal inflammation.

Surgical care:

Patients who do not respond to medical treatment of topical and oral antifungal medications usually require surgical intervention, including corneal transplantation.

Frequent corneal debridement with a spatula is helpful; it debulks fungal organisms and epithelium and enhances penetration of the topical antifungal agent.

Approximately one third of fungal infections fail to respond to medical treatment and may result in corneal perforation. In these cases, a therapeutic penetrating keratoplasty is necessary.

The main goals of surgery are to control the infection and to maintain the integrity of the globe.

Topical antifungal therapy, in addition to systemic fluconazole or ketoconazole, should be continued following penetrating keratoplasty.

References Vaddavalli PK, Garg P, Sharma S, Sangwan VS, Rao GN,

Thomas R. Role of confocal microscopy in the diagnosis of fungal and acanthamoeba keratitis. Ophthalmology. Jan 2011;118(1):29-35.

Dunlop AA, Wright ED, Howlader SA, Nazrul I, Husain R, McClellan K. Suppurative corneal ulceration in Bangladesh. A study of 142 cases examining the microbiological diagnosis, clinical and epidemiological features of bacterial and fungal keratitis. Aust N Z J Ophthalmol. May 1994;22(2):105-10.

Kanski J Jack;Clinical ophthalmology a systemic approach;6th edition;butterworth and heinnmen.

Ramanjit Sihota,Radhika Tandon(eds);Parson’s Diseases of the Eye;15;199-200.

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