**Question:** Which of the following indicates activity of anterior uveitis?

A. Increased intraocular pressure
B. Reduced visual acuity
C. Proliferative vitreoretinopathy
D. Presence of hypopyon

**Core Concept:** Anterior uveitis, also known as iridocyclitis, is an inflammatory condition affecting the anterior part of the uvea (the middle layer of the eye containing vessels and immune cells) and the iris and ciliary body. This condition can be caused by various factors such as infections, autoimmune disorders, or malignancies.

**Why the Correct Answer is Right:** The correct answer, **D** - Presence of hypopyon, indicates activity of anterior uveitis because hypopyon is a characteristic feature of active uveitis. Hypopyon is a visible layer of inflammatory cells (predominantly neutrophils) that accumulates in the anterior chamber of the eye, leading to a cloudy, translucent appearance.

**Why Each Wrong Option is Incorrect:**

**A** - Increased intraocular pressure (IOP) is a potential complication of uveitis, but it is not an indicator of activity. IOP elevation can arise due to uveitis-induced trabecular meshwork dysfunction, but it does not specifically indicate active inflammation within the uvea.

**B** - Reduced visual acuity can be a symptom of uveitis but is not specific to anterior uveitis. Visual acuity is influenced by various factors, including retinal and optic nerve involvement, which are less common in anterior uveitis.

**C** - Proliferative vitreoretinopathy is a complication of diabetic retinopathy and is not directly related to anterior uveitis. It indicates the development of abnormal blood vessels in the retina and vitreous body, not anterior uveitis activity.

**Explanation of the Core Concept:**

Anterior uveitis is an inflammatory condition affecting the anterior part of the uvea, including the iris and ciliary body. It is a common cause of acute eye pain and redness and is a manifestation of an underlying disease process (e.g., infection, autoimmune disorders, or malignancies).

The correct answer, **D** - Presence of hypopyon, is a key indicator of active inflammation within the uvea, as it is a visible accumulation of inflammatory cells (predominantly neutrophils) in the anterior chamber of the eye, causing the eye to appear cloudy and translucent. This feature helps differentiate active uveitis from inactive or inapparent uveitis.

**Why Each Wrong Option is Incorrect:**

**A** - Increased intraocular pressure (IOP) can be a complication of uveitis but is not specific to anterior uveitis. IOP elevation can result from uveitis-induced trabecular meshwork dysfunction, but this is not directly related to anterior uveitis activity.

**B** - Reduced visual acuity can be a symptom of uveitis but is not specific to anterior uveitis. Visual acuity is influenced by various factors, including retinal and opt