Professional and Linguistic Assessments Board (PLAB) Practice Exam

What visual field defect is caused by a lesion of the right optic tract?

1. Right homonymous hemianopsia

2. Left homonymous hemianopsia

3. Bitemporal hemianopsia

4. Quadrantanopia

The correct answer is: Left homonymous hemianopsia

A lesion in the right optic tract will result in left homonymous hemianopsia. This type of visual field defect occurs because the optic tract carries nerve fibers that transmit visual information from the contralateral visual field. The right optic tract processes visual information from the left half of the visual field in both eyes. Therefore, damage to this tract means that the patient cannot see anything in their left visual field, which corresponds to the concept of homonymous hemianopsia, where the loss is consistent in both eyes for one side of the visual field. For additional context related to other options, right homonymous hemianopsia would occur with a lesion in the left optic tract, which affects the right side of both visual fields. Bitemporal hemianopsia occurs with damage to the optic chiasm, which affects the peripheral vision of both eyes. Quadrantanopia refers to the loss of vision in a quarter of the visual field, which can be due to specific lesions in the posterior optic radiations or the occipital lobe, but does not pertain to a straightforward tract lesion like the one described.