Staining with methylthioninium chloride for the diagnosis of fungal keratitis

The aim of this study was to investigate the potential efficacy of staining with methylthioninium chloride (MC) for the diagnosis of fungal keratitis. A total of 70 cases of fungal keratitis were included in the study from January 2009 to December 2010. The corneal scraping specimens of the patients were collected and stained with MC or a 10% potassium hydroxide (KOH)-based smear prior to microscopic examination. The staining results were confirmed with fungal culture and strain identification, which are recognized as 'gold standards' for the diagnosis of fungal keratitis. Among the 70 cases of fungal keratitis, 58 cases were positive and the positive rate was 82.86%. MC staining showed a positive rate of 62.86%, with higher levels of sensitivity (70.69%) and specificity (34.61%) compared with staining with the 10% KOH-based smear. The KOH-based smear showed a positive rate of 44.29% (P<0.05), a level of sensitivity of 44.83% (P<0.05) and a specificity of 17.95% (P<0.05). In addition, the MC staining showed false positive and negative rates of 25.00 and 29.31%, respectively, an accuracy index of 5.30% and positive and negative predictive values of 93.18 and 34.61%, respectively. The results indicate that MC staining is a fast and effective method for the early diagnosis of fungal keratitis.