Use of Potassium Hydroxide, Giemsa and Calcofluor White Staining Techniques in the Microscopic Evaluation of Corneal Scrapings for Diagnosis of Fungal Keratitis

Abstract

The aim of this study was to develop a quick and economical method for the diagnosis of fungal keratitis. Corneal scrapings were obtained from consecutive patients (n = 165) with clinically suspected fungal keratitis and were used for culture and to prepare two smears. Potassium hydroxide stain followed by calcofluor white stain was added to one smear and Giemsa stain followed by calcofluor white stain was added to the second. In comparison with the fungal culture results, the sensitivity of potassium hydroxide wet mounts was 81.0% and following the addition of calcofluor white was 96.6% in diagnosing fungal keratitis, whereas sensitivity using Giemsa stain was 39.7% and following the addition of calcofluor white was 98.3%. The Giemsa stain detected 23 cases of bacterial infection, of which six cases were mixed fungal and bacterial infections. Giemsa stain followed by calcofluor white was considered to be the better method for diagnosing fungal keratitis due to its high sensitivity combined with its ability to identify bacterial or mixed infections.