**Core Concept:** Horner's syndrome is a clinical condition characterized by the triad of ptosis, miosis, and anhidrosis due to a lesion involving the sympathetic chain. It is typically caused by a lesion in the cervical cord or sympathetic ganglia.

**Why the Correct Answer is Right:** Option C (Hypocalcemia) is incorrect because hypocalcemia does not directly result in Horner's syndrome. Hypocalcemia causes paresthesia, muscle weakness, tetany, and seizures, but not the specific constellation of symptoms seen in Horner's syndrome.

**Why Each Wrong Option is Incorrect:**

A. Hypothyroidism (Option A) is incorrect because hypothyroidism does not cause Horner's syndrome either. Hypothyroidism affects the autonomic nervous system, causing symptoms like constipation, dry skin, and fatigue, but not Horner's syndrome.

B. Posterior circulation stroke (Option B) is incorrect because a stroke affecting the posterior circulation would primarily affect the visual system, leading to visual disturbances rather than the specific neurological symptoms seen in Horner's syndrome.

D. Glaucoma (Option D) is incorrect because glaucoma primarily causes ocular symptoms like eye redness, pain, and visual disturbances, not the neurological symptoms of Horner's syndrome.

**Clinical Pearl:** Horner's syndrome can be caused by various conditions, including cervical cord injuries, sympathetic ganglionopathy, or tumors, making it essential for examiners to consider this condition in their differential diagnosis of patients presenting with specific neurological symptoms.