**Question:** Which of the following is the drug of choice of treatment of corneal ulcers caused by filamentous fungi?

A. Amphotericin B
B. Nystatin
C. Fluconazole
D. Itraconazole

**Core Concept:** Filamentous fungal infections, especially those affecting the cornea, can cause significant morbidity and visual impairment. Filamentous fungi are treated with antifungal agents that target the fungal cell wall, specifically inhibiting ergosterol synthesis.

**Why the Correct Answer is Right:** Amphotericin B is a polyene antifungal agent that binds to ergosterol, a vital component of fungal cell membranes, leading to membrane instability and cell death. This broad-spectrum antifungal agent is particularly effective against filamentous fungi, making it the preferred choice for treating corneal ulcers caused by these organisms.

**Why Each Wrong Option is Incorrect:**

B. Nystatin is a polyene antifungal agent, but it is primarily active against yeast and not filamentous fungi, making it an inappropriate choice for treating corneal ulcers.

C. Fluconazole is a triazole antifungal agent that primarily targets yeast and dermatophytes, not filamentous fungi. Therefore, it is an unsuitable choice for treating corneal ulcers caused by filamentous fungi.

D. Itraconazole is a triazole antifungal agent that primarily targets yeasts and dermatophytes, similar to fluconazole. It is not the most effective choice for treating corneal ulcers caused by filamentous fungi.

**Clinical Pearl:** Filamentous fungal infections, especially those affecting the cornea, should be considered in patients with risk factors such as prolonged steroid use, compromised immune systems, and previous eye trauma. Prompt diagnosis and treatment with appropriate antifungal agents like Amphotericin B can prevent severe complications and visual impairment.