**Core Concept**
The Brown sign is a clinical observation related to the diagnosis of a specific neurological condition. It is characterized by the appearance of a brownish discoloration of the optic disc due to the presence of a particular type of fluid.

**Why the Correct Answer is Right**
The Brown sign is seen in papilledema, which is the swelling of the optic disc due to increased intracranial pressure. In papilledema, there is a breakdown of the blood-retinal barrier, leading to the accumulation of fluid in the retina and the subsequent formation of a brownish discoloration of the optic disc, known as the Brown sign. This is a significant clinical finding that helps in the diagnosis of conditions such as idiopathic intracranial hypertension.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the Brown sign is not typically associated with optic neuritis, which is characterized by inflammation of the optic nerve.
**Option B:** This option is incorrect because the Brown sign is not seen in normal tension glaucoma, which is a condition characterized by progressive optic nerve damage despite normal intraocular pressure.
**Option C:** This option is incorrect because the Brown sign is not associated with retinal detachment, which is a condition where the retina separates from the underlying tissue.

**Clinical Pearl / High-Yield Fact**
The Brown sign is an important clinical finding that helps in the diagnosis of papilledema and increased intracranial pressure. Remember that the Brown sign is characterized by a brownish discoloration of the optic disc, which is a critical differentiator from other conditions that may present with similar symptoms.

**Correct Answer:** D.