**Core Concept**
The extraocular muscles are responsible for controlling eye movements. The intorsion movement of the eye is a specific action that involves rotating the top of the eye towards the nose. This movement is essential for maintaining binocular vision and depth perception.

**Why the Correct Answer is Right**
Intorsion is achieved through the action of the inferior oblique muscle. This muscle is one of the four rectus muscles, along with the superior rectus, medial rectus, and lateral rectus, which control the primary movements of the eye (up, down, in, out, and rotation). The inferior oblique muscle is unique in its ability to intort the eye, which is essential for maintaining proper alignment of the visual axes.

**Why Each Wrong Option is Incorrect**
* **Option A:** The superior oblique muscle is actually an extorter of the eye, not an intorter. It helps to rotate the top of the eye away from the nose.
* **Option B:** The medial rectus muscle is responsible for adduction (moving the eye towards the nose), not intorsion.
* **Option C:** The lateral rectus muscle is responsible for abduction (moving the eye away from the nose), not intorsion.

**Clinical Pearl / High-Yield Fact**
The inferior oblique muscle is often involved in strabismus (crossed eyes) and other ocular motor disorders, making it an important muscle to consider in the evaluation and treatment of eye movement abnormalities.

**Correct Answer:** D. Inferior oblique muscle.