**Core Concept**
Horner's syndrome is a neurologic disorder characterized by a disruption in the sympathetic nerves supplying the eye. It typically presents with a triad of ptosis, miosis, and anhidrosis due to the interruption of sympathetic fibers.

**Why the Correct Answer is Right**
The correct answer will be a feature that does not belong to Horner's syndrome. The key features of Horner's syndrome are due to the interruption of sympathetic fibers. Miosis, anhidrosis, and ptosis are all a direct result of the disruption of these fibers.

**Why Each Wrong Option is Incorrect**
**Option A:** Ptosis - This is actually a feature of Horner's syndrome, due to the disruption of sympathetic fibers that supply the superior tarsal muscle, leading to drooping of the eyelid.
**Option B:** Miosis - This is also a feature of Horner's syndrome, resulting from the interruption of sympathetic fibers that supply the dilator pupillae muscle, leading to constriction of the pupil.
**Option C:** Enophthalmos - This is actually a feature of Horner's syndrome, resulting from the disruption of sympathetic fibers that supply the orbital muscles, leading to a sunken appearance of the eye.

**Clinical Pearl / High-Yield Fact**
One way to remember the features of Horner's syndrome is to use the mnemonic "PTM" for ptosis, miosis, and anhidrosis.

**Correct Answer: D.**