**Core Concept**
The inferior oblique muscle is one of the six extraocular muscles responsible for controlling eye movements. Its secondary action is a complex movement that involves a combination of rotations and translations of the eyeball.

**Why the Correct Answer is Right**
The secondary action of the inferior oblique muscle is to rotate the eyeball laterally (outward) in the orbit, which is achieved through its insertion on the sclera of the globe. This action occurs due to the muscle's anatomical orientation, which allows it to generate a force that counteracts the primary action of the superior oblique muscle. The inferior oblique muscle's secondary action is essential for maintaining binocular vision and preventing diplopia (double vision) during lateral gaze.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the inferior oblique muscle's primary action is to rotate the eyeball downward, not upward.
**Option B:** This option is incorrect because the inferior oblique muscle does not have a direct effect on convergence, which is the inward movement of the eyes during binocular vision.
**Option C:** This option is incorrect because the inferior oblique muscle's secondary action is not to rotate the eyeball medially (inward), but rather laterally (outward).

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the inferior oblique muscle's secondary action is a critical component of normal binocular vision, and its dysfunction can lead to complex eye movement disorders, such as esotropia (crossed eyes).

**Correct Answer:** D.