**Core Concept**
The Doll's eye phenomenon, also known as the oculocephalic reflex, is a neurological sign that tests the integrity of the brainstem and cranial nerve VIII. It involves the movement of the eyes in response to head rotation.

**Why the Correct Answer is Right**
When a comatose patient exhibits the Doll's eye phenomenon, it indicates that the brainstem and cranial nerve VIII are functional. In this reflex, the eyes move in the direction of the head rotation due to the vestibulo-ocular reflex (VOR), which is mediated by the vestibular apparatus in the inner ear and the brainstem. The VOR helps to stabilize the image on the retina during head movement.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the vestibulo-ocular reflex (VOR) is the correct mechanism underlying the Doll's eye phenomenon, not the corneal reflex.
**Option B:** This option is incorrect because the gag reflex is not related to the Doll's eye phenomenon.
**Option C:** This option is incorrect because the pupillary light reflex is not directly related to the Doll's eye phenomenon.

**Clinical Pearl / High-Yield Fact**
The Doll's eye phenomenon is an important clinical sign that can indicate brainstem function in comatose patients. It is often used in conjunction with other neurological examination findings to assess the level of consciousness and the integrity of the brainstem.

**Correct Answer: C. Convergence-retraction nystagmus is another term for this phenomenon.