**Core Concept:** Buphthalmos is a condition characterized by abnormally enlarged eyeballs due to various causes such as uveitis, glaucoma, or hypotony. It leads to structural and functional changes in the eye, potentially causing vision loss.

**Why the Correct Answer is Right:** The correct answer, **C. Vision impairment**, is the most common symptom of buphthalmos because the enlarged eyeball disturbs the normal optical path, leading to reduced visual acuity and ocular motility impairment. This results in blurred vision, photophobia, and discomfort.

**Why Each Wrong Option is Incorrect:**

A. **D. Iris enlargement**: While iris enlargement may be present in some cases of buphthalmos, vision impairment is the more significant symptom.

B. **Glaucoma**: Although glaucoma can be a consequence of buphthalmos, it is not the most common symptom. Vision impairment takes precedence.

D. **Anterior uveitis**: While anterior uveitis can contribute to buphthalmos, vision impairment is the primary symptom, making it the correct answer choice.

**Clinical Pearl / High-Yield Fact:** Buphthalmos should be promptly diagnosed and managed to prevent further vision loss and protect the patient's quality of life. Prompt evaluation and management are essential, especially in cases of hypotony-related buphthalmos, which can lead to severe vision loss if left untreated.