**Core Concept**
Fungal corneal ulcers are a specific type of corneal infection caused by fungi, typically seen in immunocompromised patients, contact lens wearers, or those with a history of trauma. The presence of certain clinical features can help differentiate fungal corneal ulcers from bacterial or other types of ulcers.

**Why the Correct Answer is Right**
Fungal corneal ulcers are characterized by a lack of significant inflammation, a relatively slow progression, and a distinctive feathery or fluffy appearance at the edge of the ulcer. The presence of these features is crucial in making a diagnosis of fungal corneal ulcer. In contrast, bacterial ulcers typically present with significant inflammation, a rapid progression, and a well-defined edge. The correct answer is related to a clinical feature that is more suggestive of a bacterial or other type of corneal ulcer.

**Why Each Wrong Option is Incorrect**
* **Option A:** The presence of a hypopyon (accumulation of pus in the anterior chamber) can be seen in both bacterial and fungal corneal ulcers, making it an unreliable distinguishing feature.
* **Option B:** A history of trauma is a risk factor for both bacterial and fungal corneal ulcers, and its presence does not rule out a fungal etiology.
* **Option C:** The presence of a significant inflammatory response can be seen in both bacterial and fungal corneal ulcers, particularly in immunocompromised patients.

**Clinical Pearl / High-Yield Fact**
The "feathery" or "fluffy" appearance at the edge of the ulcer is a classic clinical feature of fungal corneal ulcers. This feature is often described as a "feathery" or "brush-like" appearance, and is a key differentiator from bacterial ulcers.

**Correct Answer: D.**