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Early diagnosis of mycotic keratitis: predictive value of potassium hydroxide preparation
S Sharma1, M Silverberg, P Mehta
1L.V. Prasad Eye Institute, Hyderabad, India. savitri@lvpeye.stph.net
Abstract:
Potassium hydroxide (KOH) preparation is an underutilized modality in the diagnosis of mycotic keratitis. We have earlier shown its utility in the diagnosis of Nocardia and Acanthamoeba keratitis. The aim of this study was (i) to evaluate the sensitivity, specificity and predictive value of KOH preparation, and (ii) to compare its efficacy with other methods of corneal scraping examination, for the diagnosis of mycotic keratitis. The study was conducted in two phases. In phase I, randomized corneal scrapings were examined by KOH, Gram's stain, and lactophenol cotton blue (LPCB) in 91 infectious keratitis subjects. In phase II, 53 corneal scrapings were stained with KOH and calcofluor white (CFW), and viewed with bright field (KOH) and fluorescence (CFW) microscopy. The KOH and CFW readings were recorded by an observer masked to the clinical findings and culture results. Nineteen scrapings were examined by two masked observers. In 22 culture positive fungal keratitis patients in phase I, the sensitivity of KOH, Gram's stain, and LPCB methods was 100%, 86.4%, and 77.3%, respectively. In phase II, the specificities of KOH and CFW were identical (83.8%), while the sensitivities were 81.2% and 93.7%, respectively (p = 0.59), in 16 culture positive mycotic keratitis patients. There was no significant difference between the negative and positive predictive values of KOH and CFW. Furthermore, no significant interobserver variability was found in the specificity and sensitivity. The KOH method compares well with other microscopy methods in the diagnosis of keratomycosis and has a definite place in the armamentarium of diagnostic techniques.
Insights
Potassium hydroxide (KOH) preparation is a highly sensitive and specific diagnostic tool for fungal keratitis. This method effectively aids in diagnosing mycotic keratitis, comparing favorably with other microscopy techniques.
Area of Science:
- Ophthalmology
- Mycology
- Diagnostic Microbiology
Background:
- Mycotic keratitis diagnosis often relies on various microscopy techniques.
- Potassium hydroxide (KOH) preparation's utility in diagnosing fungal keratitis requires further evaluation.
- Previous studies highlighted KOH's effectiveness for Nocardia and Acanthamoeba keratitis.
Purpose of the Study:
- To assess the sensitivity, specificity, and predictive value of KOH preparation for diagnosing mycotic keratitis.
- To compare the efficacy of KOH preparation with other corneal scraping examination methods.
Main Methods:
- Phase I: 91 infectious keratitis cases examined using KOH, Gram's stain, and lactophenol cotton blue (LPCB).
- Phase II: 53 corneal scrapings stained with KOH and calcofluor white (CFW) using bright field and fluorescence microscopy.
- Interobserver variability assessed on 19 samples.
Main Results:
- In Phase I, KOH sensitivity was 100% for fungal keratitis (22 cases), compared to 86.4% for Gram's stain and 77.3% for LPCB.
- In Phase II, KOH and CFW showed identical specificity (83.8%), with sensitivities of 81.2% for KOH and 93.7% for CFW.
- No significant differences in predictive values between KOH and CFW; low interobserver variability.
Conclusions:
- Potassium hydroxide (KOH) preparation demonstrates high sensitivity and specificity in diagnosing mycotic keratitis.
- KOH preparation is a valuable and effective diagnostic method for fungal keratitis, comparable to other microscopy techniques.
- KOH preparation should be considered a standard diagnostic tool for keratomycosis.