Question

Where is the lesion most likely in a bitemporal hemianopia?

a. tract after chiasm
b. tract on its way back to visual cortex after geniculate body
c. one of the optic nerves before the chiasm
d. optic chiasm

Answer 1

Bitemporal hemianopia is most likely caused by a lesion at the optic chiasm, often due to a pituitary tumor pressing on the crossing fibers responsible for peripheral vision.

Step-by-step explanation:

In the case of bitemporal hemianopia, the lesion is most likely at the optic chiasm. This condition is characterized by the loss of peripheral vision on the outer (temporal) halves of both visual fields. The optic nerves from both eyes meet at the optic chiasm where fibers carrying information from the peripheral visual fields cross over to the opposite side of the brain. When a lesion, such as a pituitary tumor, presses on the optic chiasm, it can specifically damage these crossing fibers, resulting in a bilateral loss of the peripheral visual fields.

However, the axons that do not decussate (i.e., those that project to the same side of the brain) remain unaffected and thus central vision is typically preserved in bitemporal hemianopia.Bitemporal hemianopia is most likely caused by a lesion at the optic chiasm, often due to a pituitary tumor pressing on the crossing fibers responsible for peripheral vision.