**Question:** Nummular keratitis is a feature of:

A. Herpes simplex virus infection
B. Tinea corporis
C. Pityriasis rosea
D. Lyme disease

**Core Concept:**
Nummular keratitis is a specific type of keratitis characterized by circular, coin-shaped lesions on the cornea. This condition is typically caused by bacterial infections, specifically Staphylococcus aureus and Streptococcus pyogenes. Infections are often associated with underlying immunodeficiency, and the condition is more common in men between 30-60 years of age.

**Why the Correct Answer is Right:**
The correct answer is D, Lyme disease, because nummular keratitis is a manifestation of Lyme disease-induced keratitis. Lyme disease is caused by the bacterium Borrelia burgdorferi, which is transmitted to humans through the bite of infected black-legged ticks. The infection can lead to various ocular manifestations, including nummular keratitis.

**Why Each Wrong Option is Incorrect:**
A, Herpes simplex virus infection (HSV), is another cause of keratitis but does not present with nummular keratitis lesions. HSV keratitis is typically characterized by diffuse, irregular, and painful ulcers.

B, Tinea corporis (ringworm), is a fungal infection affecting the skin, not the cornea. Tinea corporis presents with ring-shaped, scaly, and itchy skin lesions.

C, Pityriasis rosea (rose spots), is a skin condition characterized by a single large herald patch followed by smaller satellite lesions. Nummular keratitis does not manifest as rose spots on the skin.

**Clinical Pearl:**
Understanding the clinical features and differential diagnosis is crucial for proper diagnosis and management of eye disorders. Ocular manifestations of Lyme disease are often misdiagnosed as other conditions, leading to delayed treatment and potential complications.

**Correct Answer:** D, Lyme disease.