**Question:** Person is not able to look down. Which extraocular muscle is affected?

**Core Concept:** Extraocular muscles are a group of six pairs of muscles that control the movement of the eyes. These muscles are responsible for the six basic eye movements: upgaze, downgaze, rightward gaze, leftward gaze, inward gaze, and outward gaze.

**Why the Correct Answer is Right:** The correct answer is **C. inferior rectus muscle**. The inferior rectus muscle is responsible for downward gaze. When this muscle is affected, the individual will have difficulty or inability to look downwards.

**Why Each Wrong Option is Incorrect:**

A. **Superior rectus muscle**: This muscle is responsible for upward gaze and would not cause difficulty in looking downwards.
B. **Inferior oblique muscle**: This muscle is involved in downward and medial movements of the eye but would not cause difficulty in looking downwards.
D. **Superior oblique muscle**: This muscle is involved in downward and lateral movements of the eye but would not cause difficulty in looking downwards.

**Clinical Pearl:** A lesion affecting the inferior rectus muscle can lead to a condition known as "accommodation-convergence insufficiency" or "incomplete ductions". This condition presents with difficulty in looking downwards and may also involve a reduced ability to accommodate (focus) and converge (bring the eyes together) when viewing near objects.

**Correct Answer:** C. Inferior rectus muscle