KOH exams are one of the fundamental skills we are must possess to be good at taking care of peoples's skin. The trick to a good KOH exam is to get adequate scale, ensure the patient has not had antifungals prior to the exam, preparing the slide properly and knowing what a positive exam looks like.
When scraping for a KOH, get far more scale than you think youneed. Try to get it from inflamed and noninflamed areas, and after scrpaing the scale onto the lside, drop the KOH solution (we use Swarz-Lamkins) onto the slide, and then lightly heat the slide until the small bubbles underneath the cover slip expand, but before the fluid boils.
After slide prep, expect the slide to be readable: no thick scale on the slide, good stain, all the carbon suet removed from the slide. Examine the slide by using a quick up and down motion of the objective, it will help you identify which are real hyphal elements and which are just cell borders.
This slide is very positive, as demonstrated by the parallel margins of the cell walls of the hyphal elements, the septations and the branches coming off the main hyphae.