**Question:** Lesion in the optic chiasma causes -

A. Loss of vision in the nasal quadrants of both eyes
B. Loss of vision in the temporal quadrants of both eyes
C. Loss of vision in the inferior quadrants of both eyes
D. Loss of vision in the superior quadrants of both eyes

**Core Concept:**
The optic chiasm is a structure located in the sella turcica, where the optic nerves from both eyes cross to form the optic tracts. Optic chiasm lesions can affect vision in a specific pattern based on the extent of the injury.

**Why the Correct Answer is Right:**
A lesion in the optic chiasm primarily affects the vision in the nasal quadrants of both eyes, as the nasal fibers from each eye cross at the optic chiasm. This results in a characteristic pattern of visual field defects, known as bitemporal hemianopia.

**Why Each Wrong Option is Incorrect:**
B. Loss of vision in the temporal quadrants of both eyes (Option B) is not a typical presentation for optic chiasm lesions, as the temporal fibers do not cross at the optic chiasm.
C. Loss of vision in the inferior quadrants of both eyes (Option C) is incorrect because the optic chiasm is located superior to the level of the optic disc, affecting vision in the nasal quadrants, not inferior quadrants.
D. Loss of vision in the superior quadrants of both eyes (Option D) is not a typical presentation for optic chiasm lesions, as the superior fibers do not cross at the optic chiasm.

**Clinical Pearl:**
Understanding the pattern of visual field defects from optic chiasm lesions is crucial in differentiating it from other causes of bitemporal hemianopia, such as optic nerve lesions or optic tract lesions. This knowledge helps in narrowing down the differential diagnosis, guiding further investigations and management strategies.