**Core Concept**
Homonymous hemianopsia is a type of visual field defect characterized by the loss of half of the visual field on the same side in both eyes. This condition results from damage to the visual pathway that affects the transmission of visual information from the retina to the brain.

**Why the Correct Answer is Right**
Lesions at the optic tract level cause homonymous hemianopsia because the optic tracts are responsible for transmitting visual information from the opposite visual field of each eye to the contralateral visual cortex. Damage to the optic tract disrupts this transmission, leading to a loss of vision in the same half of the visual field in both eyes. This is because the optic tracts are the first point of decussation (crossing) in the visual pathway, where the nasal fibers (carrying information from the contralateral visual field) cross over to the opposite side of the brain.

**Why Each Wrong Option is Incorrect**
**Option A:** The visual cortex is responsible for processing visual information, but lesions here would cause more complex visual field defects, such as cortical blindness or visual agnosia, rather than homonymous hemianopsia.

**Option B:** Optic radiation is the pathway that carries visual information from the lateral geniculate nucleus to the visual cortex. Damage to the optic radiation would cause visual field defects, but not typically homonymous hemianopsia.

**Option D:** Optic chiasma lesions cause bitemporal hemianopsia, where the loss of vision is in the outer half of each visual field. This is because the optic chiasm is the point where the nasal fibers from each eye cross over, and damage here affects the transmission of visual information from the temporal fields of each eye.

**Clinical Pearl / High-Yield Fact**
In addition to homonymous hemianopsia, lesions at the optic tract level can also cause other visual field defects, such as quadrantanopsia (loss of one quarter of the visual field) or pie-in-the-sky syndrome (loss of the upper visual field).

✓ Correct Answer: C. Optic tract