Brown skin cornea is seen in -a) Siderosisb) Mustard gas exposurec) Chalcosisd) Argyrosis

**Core Concept**
Brown skin cornea is a condition characterized by the deposition of metals or other substances in the cornea, leading to a discoloration resembling a brown skin. This condition is often associated with occupational or environmental exposure to certain metals.

**Why the Correct Answer is Right**
The correct answer is related to the deposition of silver in the cornea, which is a known side effect of silver nitrate exposure. This deposition can occur in the form of a brown discoloration, giving the appearance of "brown skin" on the cornea. The deposition of silver in the cornea is due to the reduction of silver ions to metallic silver, which then precipitates in the corneal tissue.

**Why Each Wrong Option is Incorrect**
**Option A:** Siderosis refers to the deposition of iron in the tissues, which can occur in cases of iron poisoning or exposure to iron-containing foreign bodies. However, it does not typically cause a brown skin cornea.

**Option B:** Mustard gas exposure can cause corneal damage and vision loss, but it is not typically associated with the deposition of metals or a brown skin cornea.

**Option C:** Chalcosis refers to the deposition of copper in the tissues, which can occur in cases of copper toxicity or exposure to copper-containing foreign bodies. While chalcosis can cause a range of ocular symptoms, it is not typically associated with a brown skin cornea.

**Option D:** Argyrosis refers to the deposition of silver in the tissues, which can occur in cases of silver nitrate exposure. While argyrosis can cause a range of ocular symptoms, it is not the most specific answer choice for brown skin cornea.

**Clinical Pearl / High-Yield Fact**
Brown skin cornea is a classic sign of argyrosis, and it is essential to consider this condition in patients with a history of silver nitrate exposure.

**Correct Answer:** D. Argyrosis