**Core Concept**
Macular sparing is a phenomenon observed in the visual pathway where there is a relative preservation of vision in the central part of the visual field despite damage to the visual pathway. This is due to the dual blood supply to the visual cortex, specifically the Meyer's loop and the lateral occipital branch of the posterior cerebral artery.

**Why the Correct Answer is Right**
The correct answer is **B. Optic radiation in Meyer's loop**. This is because lesions affecting the optic radiation in Meyer's loop can cause damage to the visual pathway, but the contralateral optic radiation may still supply the central part of the visual field, resulting in macular sparing. The Meyer's loop is a critical area in the optic radiation where the visual fibers cross, and damage to this area can lead to visual field defects, but macular sparing may still be observed due to the dual blood supply.

**Why Each Wrong Option is Incorrect**
* **Option A:** Lesions in the optic nerve can cause unilateral blindness, but macular sparing is not typically associated with optic nerve damage.
* **Option C:** Lesions in the optic chiasm can cause bitemporal hemianopia, but macular sparing is not typically associated with optic chiasm damage.

**Clinical Pearl / High-Yield Fact**
Macular sparing is a critical concept in neuro-ophthalmology, and it is essential to remember that the Meyer's loop is a vulnerable area in the optic radiation where damage can lead to visual field defects, but macular sparing may still be observed due to the dual blood supply.

**Correct Answer:** B. Optic radiation in Meyer's loop.