Korean J Ophthalmol.  2024 Apr;38(2):98-104. 10.3341/kjo.2023.0106.

Efficacy and Rapidity of Potassium Hydroxide Mount and Modified Chicago Sky Blue 6B Stain with Potassium Hydroxide in Fungal Keratitis Detection

• Warnnissorn P
• Sawatdiwithayayong J
• Surit P

• KMID: 2554163
• DOI: http://doi.org/10.3341/kjo.2023.0106

Abstract

Purpose
To compare the efficacy and rapidity of direct microscopic detection of fungal elements from corneal ulcers between 10% potassium hydroxide (KOH) and 1% Chicago Sky Blue 6B (CSB) in 10% KOH (CSB-KOH).
Methods
Thirty patients with clinically suspected fungal keratitis were recruited. Participants with impending corneal perforation were excluded. Two slides were smeared with corneal ulcer scrapings from the ulcer’s edge and base for comparison of fungal staining solutions. One slide was infused with KOH, and the other slide was filled with CSB-KOH. Additional scraping was collected for inoculation on Sabouraud dextrose agar for fungal culture. The sensitivity, specificity and rapidity of both stainings were analyzed.
Results
The sensitivity of fungal culture, KOH, and CSB-KOH were 43.75% (95% confidence interval [CI], 19.75%–70.12%), 62.50% (95% CI, 35.43%–84.80%), and 87.50% (95% CI, 61.65%–98.45%), respectively. The specificity were 100% (95% CI, 69.15%–100%) of both stainings and fungal culture which analyzed from 16 fungal keratitis cases by laboratory and clinical diagnosis. Mean CSB-KOH examination time was quicker than KOH with the mean time difference of 5.6 minutes (95% CI, 3.22–7.98 minutes) and p-value < 0.001.
Conclusions
CSB-KOH was more effective and faster than KOH in detecting fungal elements from corneal ulcers. Therefore, CSB-KOH may be beneficial in diagnosing fungal keratitis and preventing blindness. Moreover, to the best of our knowledge, this is the first use of CSB stain in fungal keratitis detection.

Keyword

Chicago Sky Blue 6B; Corneal scraping; Fungal keratitis; Potassium hydroxide stain