Homonymous hemianopia is seen in lesion of -a) Optic tractb) Optic chiasmac) Optic radiationd) Optic nervee) Occipital cortex
## **Core Concept**
Homonymous hemianopia refers to a visual field defect where one half of the visual field is affected on the same side in both eyes. This condition results from lesions affecting the visual pathway posterior to the optic chiasm.
## **Why the Correct Answer is Right**
The correct answer, **a) Optic tract**, is right because a lesion in the optic tract affects the fibers from the ipsilateral temporal hemiretina and contralateral nasal hemiretina, leading to a homonymous hemianopic visual field defect. This is due to the anatomy of the visual pathway: the optic nerves from both eyes partially cross at the optic chiasm, and the optic tracts carry information from both eyes that is representative of the same visual field.
## **Why Each Wrong Option is Incorrect**
- **Option B: Optic chiasm** - Lesions here typically cause bitemporal hemianopia (loss of outer fields in both eyes) due to the crossing of nasal fibers from each optic nerve.
- **Option D: Optic nerve** - A lesion here causes loss of vision in one eye (monocular blindness), not homonymous hemianopia.
- **Option C: Optic radiation** and **Option E: Occipital cortex** - While lesions here can cause visual field defects, they typically cause homonymous hemianopia as well. However, the question seems to seek the most direct and classic association, which is with the optic tract. Optic radiation and occipital cortex lesions can cause more variable field defects depending on their exact location.
## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the visual pathway can be divided into anterior (pre-chiasmal) and posterior (post-chiasmal) parts. Lesions in the posterior part (optic tract, optic radiation, and occipital cortex) can cause homonymous visual field defects. Specifically, for homonymous hemianopia, the optic tract is a critical site.
## **Correct Answer: A. Optic tract**