Use of lactophenol cotton blue mounts of corneal scrapings as an aid to the diagnosis of mycotic keratitis

Lactophenol cotton blue (LPCB) mounts of corneal ulcer scrapings were assessed as a diagnostic tool in cases of mycotic keratitis over a period of 15 months. We investigated 568 cases of ulcerative keratitis by microbiological techniques consisting of direct microscopic examination of LPCB mounts and Gram-stained smears as well as culture of material scraped from the ulcer. Fungi were isolated in large numbers on multiple media from the corneal scrapings of 179 patients (culture-proven mycotic keratitis). Direct microscopic examination of LPCB mounts of corneal scrapings yielded positive results in 140 (78%) of 179 culture-positive patients and negative results in 371 (95%) of 389 culture-negative patients. There was a significant difference between the percentage of positive results obtained by LPCB mounts and by Gram-stained smears in the culture-positive cases. The LPCB mount was positive in greater than 80% of cases of keratitis due to Fusarium spp. and Aspergillus spp. The LPCB mount is strongly recommended as a simple, rapid, inexpensive, and sensitive diagnostic technique in cases of mycotic keratitis.