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Fungal keratitis

Disease name and synonyms

Fungal keratitis

Fungi responsible

Aspergillus flavus, Aspergillus fumigatus, occasionally other Aspergillus spp. Fusarium spp. Candida albicans, less common species include Curvularia lunata, Scedosporium apiospermum, Bipolaris spp., Lasiodiplodia theobromae, Cephaliophora irregularis,  Colletotrichum dematium and others.

Disease description

Follows ocular injury (~50%) or contaminated contacts lens fluid, invasion of the transparent cornea by fungi leads to inflammation and loss of vision. Symptoms include usually as in any other type of keratitis, but, perhaps, more prolonged in duration (five to ten days).

Frequency and global burden

Bacterial keratitis is more common in contact lens wearers and the western world, whereas in India and Nepal and some other countries, fungal keratitis is at least as common as bacterial keratitis. There are estimated to be over a million cases of fungal keratitis annually worldwide most in tropical countries.

Underlying problems and at risk patients

Trauma especially if associated with plant material is a common antecedent to fungal keratitis. Contact lens fluid contaminated with fungi (ie Fusarium) may lead to a mini-outbreak of fungal keratitis. Other possible risk factors include topical corticosteroids, traditional medicines and higher external temperatures and humidity.

Diagnostic testing

The best diagnostic specimen is material from the affected part of the cornea collected by scraping any area of ulceration or biopsy when the corneal epithelium is intact and the infection is within the corneal stroma.  Material should be collected from the base and edges of the ulcerated part of the cornea. Calcium alginate swabs premoistened with tryptone soy broth used for debridement may facilitate recovery of fungi in culture. Microscopy (lactophenol cotton blue, gram stain and Calcofluor white) and culture (and possibly PCR) are necessary, because of the wide variety of fungi involved. Prolonged culture (3 weeks) at 25ºC or 30ºC may be necessary. 

How to take a corneal scrape by Astrid Leck as published in "COMMUNITY EYE HEALTH JOURNAL VOLUME 28 ISSUE 89 | 2015" 1-20

Treatments

Topical antifungal therapy is essential, with the severity of the disease dictating how frequently eye drops are administered. In severe cases this is hourly, and can be reduced in frequency after 1- days as improvement is documented. For superficial lesions caused by filamentous fungi, topical natamycin 5%, amphotericin B 0.15% or voriconazole 2-3% (50µg/ml) are usually used. For Candida infections, amphotericin B 0.15% or voriconazole 2-3% may be used. For severe infections, oral therapy is also advised, voriconazole, fluconazole (if Candida) or itraconazole (if Aspergillus). Alternative therapies include topical (1%) and subconjunctival (10 mg) miconazole or topical itraconazole suspension (1%). Therapy is usually continued for at least 14 days.

Topical antifungal therapy has a 60% response rate with retention of vision if keratitis is severe and a 75% response if milder.

Surgical debridement is essential for severe disease (link to section under surgery).

 Managing keratitis.

Outlook and prognosis

Fungal keratitis is associated with a ~5- fold higher risk of subsequent perforation and need for penetrating keratoplasty than bacterial keratitis. Recovery of sight is higher if the diagnosis is made early.

Reviews:

Badiee 2013;  Thomas & Kaliamurthy 2013

Images

An example of severe fungal keratitis (Dr Philip Thomas, Tiruchirappalli).


Complete corneal opacifiaction following fungal keratitis; that is only remediable with a corneal transplant.

 

Videos

 

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