Evaluation of impression smear in the diagnosis of fungal keratitis.

ABSTRACT

PURPOSE: To evaluate and compare impression smear with the conventional mechanical corneal scraping by potassium hydroxide (KOH) method in the diagnosis of fungal keratitis. MATERIALS AND METHODS: Fifty consecutive cases of clinically suspected fungal keratitis were included. Under topical anesthesia, impression smear was obtained from the lesion, followed by the conventional mechanical scraping and both were transferred to sterile glass slides. The slides were examined under direct microscopy with KOH 10% wet mount. Impression smear KOH was compared with the scraping KOH and culture. RESULTS: The KOH smear was positive in 36 (72%) patients with impression smear technique and positive in 35 (70%) patients from corneal scrapings. Sensitivity of impression smear technique as compared to scraping was 97.14%, specificity 92.86%, positive predictive value 94.4%, negative predictive value 92.86%, false positive rate 5.56%, false negative rate 7.14% and accuracy was 94%. As compared to culture, the sensitivity was 100%, specificity 46.67%, positive predictive value 55.56%, negative predictive value 100%, false positive rate 53.33%, false negative rate 0% and accuracy was 68%. CONCLUSION: Impression smear KOH examination is comparable to conventional mechanical corneal scraping KOH examination in making a tentative diagnosis of fungal keratitis and can be accurately relied upon for initiating anti-fungal therapy.