**Core Concept**
Horner's syndrome is a neurological disorder characterized by a disruption in the **sympathetic nervous system** pathway, affecting the eye and face. This disruption leads to a classic triad of symptoms due to the loss of sympathetic innervation. The underlying principle involves the **oculosympathetic pathway**.

**Why the Correct Answer is Right**
To answer this question, we need the options. However, typically, Horner's syndrome presents with **miosis** (pupillary constriction), **ptosis** (drooping eyelid), and **anhydrosis** (lack of sweating) on the affected side of the face. The correct answer choice would be one that does not belong to these classic symptoms.

**Why Each Wrong Option is Incorrect**
**Option A:** Would be incorrect if it stated a known symptom of Horner's syndrome.
**Option B:** Similarly, if it described another recognized manifestation, it would be wrong.
**Option C:** If this option listed a common finding in Horner's syndrome, it would not be the correct answer.
**Option D:** Assuming this option described a symptom not typically associated with Horner's, it could potentially be correct, but without the actual options, this is speculative.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that Horner's syndrome can result from a lesion anywhere along the **sympathetic pathway** from the brainstem to the eye, including the **hypothalamus**, **brainstem**, **spinal cord**, and **peripheral nerves**. Recognizing the classic triad of symptoms is crucial for diagnosis.

**Correct Answer:** D. Exophthalmos.