Fungal Keratitis Workup

  • Author: Daljit Singh, MBBS, MS, DSc; Chief Editor: Hampton Roy Sr, MD   more...
 
Updated: Oct 27, 2011
 

Laboratory Studies

The diagnosis of fungal keratitis continues to be problematic. Many clinical characteristics are not specific to fungal ulcers; therefore, antifungal therapy should be withheld until a diagnosis is confirmed by laboratory studies.

The most important step in the initial management of suspected fungal keratitis is to obtain corneal material for directed smears and inoculation of media. Smears are used to obtain rapid information about the pathogen. Gram stain identifies yeast, and Giemsa stain is useful in detecting fungal elements. However, if fluorescein microscopy is available, acridine orange and calcofluor white are the stains of choice. The primary isolation cultures for fungus are Sabouraud and blood agar at room temperature.

In all patients with suspected fungal keratitis, initial corneal smears and cultures should be performed. Culture media for suspected fungal keratitis should include the same media used for a general infectious-keratitis workup.

  • 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.
  • Brain-heart infusion broth is another medium that can be used.
  • Cycloheximide should not be present in the medium because it inhibits fungal growth.
  • Corneal scrapings provide for initial debridement of organisms and epithelium, which may be a barrier to antifungal penetration.
  • Gram and Giemsa stains of corneal scrapings have sensitivities of about 50% in establishing a diagnosis. Calcofluor white stain (requires a fluorescent microscope) also can identify fungal organisms.
  • Initial growth in culture occurs within 72 hours in 83% of cultures and within 1 week in 97% of cultures.
  • A waiting period of 2 weeks is usually necessary for confirmation of no growth in culture.
  • Culture has been used as the criterion standard to aid ophthalmologists in the diagnosis of fungal keratitis; therefore, the true sensitivity of culture techniques is unknown.
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Imaging Studies

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

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Other Tests

The laboratory diagnosis of fungal keratitis may be problematic because of the very small sample obtained by scraping the corneal ulcer. Therefore, recent methods for the identification of fungi have been under study and include immunofluorescence staining, electron microscopy, and confocal microscopy. Confocal microscopy may help in correctly diagnosing early stages of fungal keratitis and in monitoring disease progress at the edges and depth. It may also help guide timely decision for keratoplasty and may be helpful in determining when to stop medication.[2]

The polymerase chain reaction (PCR) technique holds promise as an effective method of diagnosing fungal keratitis because it offers increased sensitivity and significant reduction in the time required to establish a diagnosis.

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Procedures

If corneal smears and cultures are negative at 48-72 hours in a patient who is strongly suspected of having a fungal infection and who is not improving on the initial, broad-spectrum antibacterial therapy, the authors recommend proceeding to a corneal biopsy to establish a diagnosis.

The corneal biopsy specimen should be submitted to the laboratory. A substantial portion also should be submitted for histopathologic examination. The pathologist should be alerted regarding the suspected diagnosis and especially that the specimen is a small piece of cornea.

A negative biopsy result indicates that the destructive corneal process is progressing, and hypopyon exists; therefore, anterior chamber paracentesis or excisional biopsy (keratoplasty) should be performed.

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Histologic Findings

Histopathologic examination of corneal buttons can reveal the presence of fungal elements in 75% of patients. Fungal hyphae usually lie parallel to the corneal surface and lamellae. The presence of vertical oriented fungal elements in regard to stromal lamellae depicts high virulence of the organism and usually is associated with more aggressive infection. The Descemet membrane may serve as a partial barrier for invasion of fungal organisms. Penetration of the Descemet membrane by the fungal elements depicts an aggressive organism and a higher risk for contamination of the globe.

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Contributor Information and Disclosures
Author

Daljit Singh, MBBS, MS, DSc  Professor Emeritis, Department of Ophthalmology, Guru Nanak Dev University, Amritsar, India; Director, Daljit Singh Eye Hospital

Daljit Singh, MBBS, MS, DSc is a member of the following medical societies: All India Ophthalmological Society, American Society of Cataract and Refractive Surgery, Indian Medical Association, International Intraocular Implant Club, and Intraocular Implant and Refractive Society, India

Disclosure: Nothing to disclose.

Coauthor(s)

Arun Verma, MD  Senior Consultant, Department of Ophthalmology, Dr Daljit Singh Eye Hospital, India

Disclosure: Nothing to disclose.

Specialty Editor Board

Anastasios J Kanellopoulos, MD  Assistant Program Director, Clinical Associate Professor, Department of Ophthalmology, Manhattan Eye, Ear, and Throat Hospital, New York University

Anastasios J Kanellopoulos, MD is a member of the following medical societies: American Academy of Ophthalmology, Association for Research in Vision and Ophthalmology, Eye Bank Association of America, and International Society of Refractive Surgery

Disclosure: Nothing to disclose.

Francisco Talavera, PharmD, PhD  Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Medscape Salary Employment

Christopher J Rapuano, MD  Professor, Department of Ophthalmology, Jefferson Medical College of Thomas Jefferson University; Director of the Cornea Service, Co-Director of Refractive Surgery Department, Wills Eye Institute

Christopher J Rapuano, MD is a member of the following medical societies: American Academy of Ophthalmology, American Society of Cataract and Refractive Surgery, Contact Lens Association of Ophthalmologists, Cornea Society, Eye Bank Association of America, International Society of Refractive Surgery, and Pan-American Association of Ophthalmology

Disclosure: Allergan Honoraria Speaking and teaching; Allergan Consulting fee Consulting; Alcon Honoraria Speaking and teaching; Inspire Honoraria Speaking and teaching; RPS Ownership interest Other; Vistakon Honoraria Speaking and teaching; EyeGate Pharma Consulting; Inspire Consulting fee Consulting; Bausch & Lomb Honoraria Speaking and teaching; Bausch & Lomb Consulting fee Consulting

Lance L Brown, OD, MD  Ophthalmologist, Affiliated With Freeman Hospital and St John's Hospital, Regional Eye Center, Joplin, Missouri

Disclosure: Nothing to disclose.

Chief Editor

Hampton Roy Sr, MD  Associate Clinical Professor, Department of Ophthalmology, University of Arkansas for Medical Sciences

Hampton Roy Sr, MD is a member of the following medical societies: American Academy of Ophthalmology, American College of Surgeons, and Pan-American Association of Ophthalmology

Disclosure: Nothing to disclose.

Additional Contributors

The authors and editors of eMedicine gratefully acknowledge the contributions of previous author, George Alexandrakis, MD, to the development and writing of this article.

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Fungal corneal ulcer.
Perforated fungal ulcer.
Fungal infection under treatment.
Perforated fungal corneal ulcer.
Fungal ulcer in an elderly woman.
Fungal ulcer.
Fungal corneal ulcer, with excessive vascularization.
Marginal ulcer, fungus positive.
Healed fungal ulcer.
Fungal keratitis.
Corneal perforation, blocked by a crystalline lens and being covered by epithelium.
Fungal keratitis, being controlled.
Fungal infection.
Fungal infection.
Fungal abscess.
Fungal corneal abscess/ulcer. A proven case of fungal infection, 5 days' duration. Intense infiltration around the abscess.
 
 
 
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