**Question:** Keratitis is caused by

A. bacteria
B. viruses
C. fungi
D. parasites

**Correct Answer:** B. viruses

**Core Concept:** Keratitis refers to inflammation of the cornea, the transparent, dome-shaped outer layer of the eye that provides protection and clear vision. Viral keratitis is an example of an infectious keratitis caused by viruses.

**Why the Correct Answer is Right:** Viral keratitis is primarily caused by viruses that infect the cornea directly or indirectly through the tear film, leading to inflammation and potential damage to the corneal cells. Two common viruses that cause viral keratitis are herpes simplex virus (HSV) and varicella-zoster virus (VZV). HSV is responsible for cold sores on the lips and can spread to the eye, while VZV is associated with chickenpox and shingles.

**Why Each Wrong Option is Incorrect:**

A. Bacteria (keratitis bacilli) are typically responsible for bacterial keratitis, a different condition characterized by bacterial invasion and inflammation of the cornea.

B. Fungi are responsible for fungal keratitis, characterized by fungal invasion and immune response. While viral keratitis can be associated with secondary fungal infection, they are not the primary cause.

C. Fungi are typically associated with mycotic infections, not specifically keratitis. Fungal keratitis is caused by fungal invasion, while fungi are not the primary cause of viral keratitis.

**Clinical Pearl:**

Viral keratitis can lead to complications such as corneal ulceration, scarring, and vision impairment if not treated promptly and effectively. Prompt diagnosis and antiviral therapy are crucial for preventing these complications and maintaining ocular health. In cases of suspected viral keratitis, consulting an ophthalmologist is essential for proper management and treatment.