**Core Concept**
Temporal pallor in the optic disc is a clinical sign characterized by a pale appearance of the optic disc's temporal aspect, often associated with optic nerve damage or atrophy. This phenomenon is typically observed in conditions affecting the optic nerve, such as inflammation, compression, or degeneration.

**Why the Correct Answer is Right**
Glaucoma is a group of eye conditions that damage the optic nerve, often due to increased intraocular pressure. However, glaucoma typically causes a more diffuse optic disc cupping rather than temporal pallor. The increased intraocular pressure in glaucoma can lead to optic nerve damage, but the characteristic changes in the optic disc are more often cupping and not temporal pallor.

**Why Each Wrong Option is Incorrect**
**Option A:** Optic neuritis is an inflammatory condition that affects the optic nerve, often presenting with pain on eye movement, visual loss, and optic disc swelling. Temporal pallor can be seen in optic neuritis due to the involvement of the optic nerve.
**Option B:** Compression of the optic nerve can cause damage to the nerve, leading to temporal pallor. Conditions like pituitary tumors or other space-occupying lesions can compress the optic nerve, resulting in this clinical sign.
**Option C:** Leber's hereditary optic neuritis is a mitochondrial disorder that affects the optic nerve, leading to progressive visual loss. Temporal pallor can be a feature of this condition due to the degeneration of the optic nerve.

**Clinical Pearl / High-Yield Fact**
Temporal pallor in the optic disc is often associated with conditions that affect the optic nerve, particularly those with an inflammatory or compressive component. It is essential to differentiate between these conditions, as the management and prognosis can vary significantly.

**✓ Correct Answer: D. Glaucoma**