**Core Concept**
Acute anterior uveitis is an inflammatory condition of the anterior chamber of the eye, characterized by the presence of inflammatory cells, flare, and often, a painful red eye. The condition affects the iris and ciliary body, leading to symptoms such as pain, photophobia, and decreased vision.

**Why the Correct Answer is Right**
The pupil in acute anterior uveitis is typically constricted due to the spasm of the iris sphincter muscle, which is a result of the inflammation in the anterior chamber. This spasm causes the pupil to become smaller and more constricted, leading to a condition known as a constricted or miosed pupil. The inflammation also leads to the release of prostaglandins, which cause the iris sphincter muscle to contract.

**Why Each Wrong Option is Incorrect**
**Option A:** A dilated pupil is not typically associated with acute anterior uveitis, as the inflammation in the anterior chamber leads to a constricted pupil.
**Option B:** A normal pupil size is not typically seen in acute anterior uveitis, as the inflammation leads to a constricted pupil.
**Option C:** A mid-dilated pupil may be seen in conditions such as iris sphincter paralysis, but it is not typically associated with acute anterior uveitis.

**Clinical Pearl / High-Yield Fact**
A constricted pupil in the context of acute anterior uveitis is a classic clinical finding that should raise suspicion for this condition, and prompt further investigation and treatment to prevent complications such as synechiae and vision loss.

**Correct Answer: C. Constricted pupil.**