## **Core Concept**
Horner's syndrome is a neurologic disorder characterized by a triad of ptosis (drooping eyelid), miosis (pupillary constriction), and anhidrosis (absence of sweating) on one side of the face. It results from disruption of the sympathetic nerves supplying the eye.

## **Why the Correct Answer is Right**
The correct answer, , indicates that anisocoria (unequal pupil size) is not a feature of Horner's syndrome; rather, miosis (constricted pupil) is. Horner's syndrome involves a disruption in the sympathetic pathway that leads to a decrease in the pupil size (miosis) on the affected side, not an increase or variability in pupil size.

## **Why Each Wrong Option is Incorrect**
* **Option A:** Ptosis is indeed a feature of Horner's syndrome. It occurs due to the interruption of sympathetic nerves supplying the superior tarsal muscle, which assists in elevating the eyelid.
* **Option B:** Anhidrosis (lack of sweating) on the face is a feature of Horner's syndrome. This occurs because of the disruption of sympathetic nerves that control sweat glands.
* **Option C:** Miosis (pupillary constriction) is a hallmark of Horner's syndrome. It results from the interruption of the sympathetic nerves that normally cause pupillary dilation.

## **Clinical Pearl / High-Yield Fact**
A key clinical point to remember is that Horner's syndrome can be distinguished from other causes of ptosis and miosis by the presence of anhidrosis on the same side of the face. Additionally, the ptosis in Horner's syndrome is typically mild.

## **Correct Answer:** . Anisocoria