**Core Concept**
Bitemporal hemianopic field defect results from compression of the optic chiasm, where the nasal fibers of both optic nerves cross. This defect is specifically due to lesions affecting the chiasm, most commonly caused by a large anterior pituitary tumor that expands into the suprasellar cistern and compresses the chiasm.

**Why the Correct Answer is Right**
A pituitary tumor, especially a large adenoma, grows posteriorly and compresses the optic chiasm. The nasal fibers of each retina cross at the chiasm and are therefore located in the anterior part. When these fibers are compressed, the temporal visual fields are lost on both sides, leading to bitemporal hemianopia. This is a classic sign of intracranial pathology involving the chiasm.

**Why Each Wrong Option is Incorrect**
Option A: Glaucoma causes a **central scotoma** or **arcuate scotoma** due to optic nerve damage, not a bitemporal defect.
Option B: Optic neuritis presents with **acute, bilateral, or unilateral visual loss** and **pain on eye movement**, not a specific bitemporal hemianopia.
Option D: Retinal detachment causes **central vision loss** with a **circular scotoma**, not a bitemporal field defect.

**Clinical Pearl / High-Yield Fact**
"**Pituitary tumor → bitemporal hemianopia**" is a classic clinical association. Always consider pituitary pathology in any patient with bitemporal hemianopia, especially with hormonal symptoms like acromegaly or Cushing’s disease.

✓ Correct Answer: C. Pituitary tumor