**Core Concept**
Fungal keratitis is a serious ocular infection caused by fungi, typically affecting the cornea. It can occur in individuals with compromised corneal integrity, such as following trauma or in patients with pre-existing corneal conditions.

**Why the Correct Answer is Right**
Fungal keratitis is characterized by its unique features, including **fever**, **severe visual impairment**, and **non-response to conventional antibiotic therapy**. The infection often presents with **severe pain** and **redness**, and can lead to **corneal perforation** if left untreated. The pathogenesis of fungal keratitis involves the invasion of fungal spores into the corneal tissue, where they multiply and cause tissue damage.

**Why Each Wrong Option is Incorrect**
**Option A:** While fever can be a feature of fungal keratitis, it is not the most distinctive characteristic.
**Option B:** Severe visual impairment is indeed a feature of fungal keratitis, making this option incorrect.
**Option C:** Non-response to conventional antibiotic therapy is a hallmark of fungal keratitis, as fungi are resistant to most antibiotics.
**Option D:** Corneal perforation is a potential complication of fungal keratitis, but it is not as specific a feature as non-response to conventional antibiotic therapy.

**Clinical Pearl / High-Yield Fact**
Remember that fungal keratitis often presents with a **delayed onset** of symptoms, making early diagnosis challenging. A thorough history, including exposure to contaminated water or soil, and a high index of suspicion, are crucial in diagnosing this condition.

**Correct Answer: B. Severe visual impairment is indeed a feature of fungal keratitis.