**Core Concept**
The Voissius ring is a clinical sign associated with a specific condition that affects the eye. It is characterized by a circular, white or grayish ring that appears around the iris. This phenomenon is related to the anatomy of the eye, specifically the interaction between the iris and the ciliary body.

**Why the Correct Answer is Right**
The Voissius ring is seen in conditions where there is an increase in intraocular pressure, causing the iris to become pushed forward and rub against the ciliary body. This results in the formation of a ring-like structure due to the deposition of inflammatory cells and tissue debris. The Voissius ring is often associated with uveitis, a form of eye inflammation that can be caused by various factors, including infections, injuries, and autoimmune disorders.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the Voissius ring is not typically associated with conditions that affect the retina, such as diabetic retinopathy or age-related macular degeneration.
**Option B:** This option is incorrect because the Voissius ring is not a characteristic feature of glaucoma, although increased intraocular pressure can contribute to its development.
**Option C:** This option is incorrect because the Voissius ring is not typically seen in conditions that affect the cornea, such as keratitis or corneal ulcers.

**Clinical Pearl / High-Yield Fact**
The Voissius ring is a classic sign of uveitis, and its presence should prompt further investigation to determine the underlying cause of the eye inflammation. Remember that the Voissius ring is a "sentinel sign" that can indicate the presence of a more serious underlying condition.

**Correct Answer:** D.