**Core Concept**
The pupillary light reflex is a complex process involving the afferent and efferent pathways of the autonomic nervous system. It is a protective mechanism to regulate the amount of light entering the eye, ensuring optimal vision. The efferent pathway of the pupillary light reflex involves the contraction of a specific muscle, leading to the constriction of the pupil.

**Why the Correct Answer is Right**
The correct muscle contracted as part of the pupillary light reflex is the sphincter pupillae. This smooth muscle is innervated by the parasympathetic division of the autonomic nervous system through the oculomotor nerve (cranial nerve III). When light enters the eye, it stimulates the retina, which sends signals to the oculomotor nerve, resulting in the contraction of the sphincter pupillae muscle. This contraction causes the pupil to constrict, reducing the amount of light entering the eye.

**Why Each Wrong Option is Incorrect**
**Option A:** The ciliary muscles are involved in changing the shape of the lens for accommodation, not in the pupillary light reflex.
**Option B:** The dilator pupillae muscle is responsible for pupil dilation, which is the opposite of the pupillary light reflex.
**Option C:** The extraocular muscles control eye movements and are not involved in the pupillary light reflex.

**Clinical Pearl / High-Yield Fact**
The pupillary light reflex is a useful clinical tool for assessing the integrity of the afferent and efferent pathways of the autonomic nervous system. A normal pupillary light reflex is essential for diagnosing conditions such as third nerve palsy or optic nerve damage.

**Correct Answer: D. Sphincter pupillae.**