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A 24-year-old contact lens wearer with unilateral vision loss requiring penetrating keratoplasty
Digital Journal of Ophthalmology 2019
Volume 25, Number 2
June 30, 2019
DOI: 10.5693/djo.03.2019.06.001
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Jonathan T. L. Lee, MBBS, BMedSc | Department of Ophthalmology, Alfred Health, Melbourne, Victoria, Australia Chengde Pham, MBBS, BMedSci | Department of Ophthalmology, Alfred Health, Melbourne, Victoria, Australia Edward Greenrod, MBBS, FRANZCO | Department of Ophthalmology, Alfred Health, Melbourne, Victoria, Australia
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| Diagnosis and Discussion | The fungus Metarhizium anisopliae was first described nearly 140 years ago and is a common insect pathogen, with a wide range of hosts comprising 200 insect species.(2) It is used commercially as a natural pesticide for biocontrol of many insect populations across the world. It is typically considered safe to humans, because optimal temperature for growth is between 25° C and 30° C, but isolates that are able to grow at temperatures near 35° C exist, particularly in tropical regions.(2)
Our search of the English-language literature yielded fewer than 10 reported cases of Metarhizium anisopliae ocular infection worldwide.(3-9) Mode of transmission typically involves agricultural exposure, with a history of vegetal trauma or soft contact lens wear. Although fungal keratitis is thought to be more common in tropical regions,(1) most published cases of Metarhizium anisopliae keratitis have arisen in temperate or extratropical climates, including Japan,(5) France,(6,7) the United States,(8) and Australia.(4) In this case, initial symptoms developed in Australia, but it is possible that the keratomycosis only became established on travel to Vietnam, which has a tropical climate and high relative humidity.
Management of filamentous fungal keratitis requires prompt identification through corneal scrapings or biopsy to aid directed therapy. The prognosis of Metarhizium anisopliae keratitis may be favorable with early administration of topical natamycin.(3,8,9) However, factors that contribute to poor visual outcomes include anterior chamber inflammation, large ulcer size, or scleral involvement.(4-7) In cases of deeper fungal invasion into the underlying corneal stroma, intraocular and systemic antifungals are recommended, and ideally tailored according to in vitro antifungal susceptibility testing.(1) Antifungal therapy should be maintained for at least 6 weeks, because negative scrapings during treatment may not exclude deep-seated fungal infection.
Surgical intervention may be required in up to 35% of patients with fungal keratitis refractory to maximal medical therapy.(10) Ideally, medical management should be provided to reduce the microbial burden, but surgery may be necessary in cases of progressive keratitis approaching the limbus or when perforation is imminent. The aim of surgery is to completely remove all infectious elements and involved tissue, and this may involve debridement, conjunctival flap, lamellar keratectomy, or penetrating keratoplasty, depending on the depth and severity of infection.(1,10) This may also include an iridectomy when the iris is involved. The poor surgical outcomes previously reported for Metarhizium anisopliae keratomycosis are likely attributable to advanced disease with associated scleral necrosis(4,5) or endophthalmitis(7) at the time of operation.
We report a case of Metarhizium anisopliae ocular infection with a favorable visual outcome following keratoplasty. Several reasons may account for the successful response in this patient, including the peripheral location of the infiltrate, aggressive targeted antifungal therapy (topical, intraocular, and systemic) based on isolate susceptibilities, and keratoplasty before scleral involvement. Fungal infections of the cornea are a challenging disease entity, and early recognition remains crucial to facilitate appropriate treatment and avoid potentially devastating outcomes.
Acknowledgments
The authors thank Drs. Helen Alexiou, Ian Ross, and Sarah Kidd, of the National Mycology Reference Centre, SA Pathology, Adelaide, South Australia, for their assistance with the microbiological identification, sensitivities, and sequencing. | |
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