A patient has an injury to the optic nerves, such that the branches of each optic nerve that normally cross to the opposite side of the brain at the optic chiasm are severed. The remaining branches, which do not cross to the other side of the brain, are intact. Which of the following best describes the effect of this injury on his vision?
A)The patient can now see only by using his right eye; his left eye is functionally blind.
B)Only information from the left visual field can enter the patient's brain for processing.
C)Only the signal for half the visual field of each eye is processed by the brain.
D)The patient's brain now receives visual information only from the medial half of each retina.

Question

Quizplus · Accepted Answer

The optic nerves from each eye carry information from both the right and left visual fields. At the optic chiasm, some of the nerve fibers from each eye cross over to the opposite side of the brain, while others stay on the same side. In this case, the branches of each optic nerve that cross over have been severed, so the remaining branches carry information only from the half of the visual field that is processed by the same side of the brain. Therefore, only the signal for half the visual field of each eye (the side ipsilateral to the intact optic nerve branches) is processed by the brain.

A Patient Has an Injury to the Optic Nerves, Such