**Core Concept:** Pupillary reflexes are involuntary responses of the pupils to light that are mediated by the parasympathetic autonomic nervous system and the Edinger-Westphal nucleus in the midbrain. The optic nerve plays a crucial role in transmitting visual information from the retina to the brain.

**Why the Correct Answer is Right:** In this scenario, a gunshot wound to the head results in the severance of the right optic nerve. This disrupts the transmission of visual information to the brain, including the Edinger-Westphal nucleus responsible for the pupillary light reflex. Consequently, the right pupil will not contract in response to light, indicating a loss of pupillary light reflex.

**Why Each Wrong Option is Incorrect:**

A. This option is incorrect because the question states that the optic nerve is severed, which directly affects the pupillary light reflex.
B. This option is incorrect because a complete severance of the optic nerve would disrupt the pupillary light reflex on both sides.
C. This option is incorrect because the optic nerve injury directly affects the pupillary light reflex.
D. This option is incorrect because the injury to the optic nerve would not cause an opposite response in the left pupil due to the direct effect on the right optic nerve.

**Why the Correct Answer is Right:** The correct answer (D) is right because the severance of the optic nerve disrupts the transmission of visual information to the brain, including the Edinger-Westphal nucleus responsible for the pupillary light reflex. Due to the injury, the right pupil will not contract in response to light, indicating a loss of the pupillary light reflex.

**Why Each Wrong Option is Incorrect:**

A. This option is incorrect because the injury directly affects the pupillary light reflex in the right eye.
B. This option is incorrect because a complete severance of the optic nerve would disrupt the pupillary light reflex on both sides.
C. This option is incorrect because the injury to the optic nerve would directly affect the pupillary light reflex in the right eye.
D. This option is the correct answer because the injury to the optic nerve disrupts the transmission of visual information to the brain, resulting in the loss of the pupillary light reflex in the right eye.

**Core Concept:** The pupillary light reflex is an important clinical sign in assessing neurological function, particularly in assessing the integrity of the optic nerve and brainstem.

**Clinical Pearl:** A sudden, disproportionate constriction of the pupil on the affected side in cases of optic nerve injuries can be a clinical sign of the injury. It is essential for medical students and practitioners to recognize such signs to appropriately diagnose and manage patients with neurological deficits.