John fell down the staircase and injured his head, causing a complete crushing/destruction of the left optic nerve. What is the consequence of this lesion for John’s overall vision?
Partial loss of the left visual field.
Complete blindness in the right eye.
Complete blindness in the left visual field.
Complete blindness in the left eye. Both A) and D) would be consequences of this lesion.
The correct answer and explanation is:
The correct answer is Complete blindness in the left eye.
Explanation:
The optic nerves carry visual information from each eye to the brain. The optic nerve fibers from each retina meet at the optic chiasm, where the fibers from the nasal side of each retina cross to the opposite side of the brain. The fibers from the temporal side of each retina do not cross and remain on the same side of the brain. This arrangement is important for processing visual information from both eyes and providing binocular vision.
In this case, if the left optic nerve is completely crushed or destroyed, it will result in the complete loss of vision in the left eye. This is because the left optic nerve is responsible for transmitting visual information from the left eye to the brain. With this nerve damaged, no information from the left eye will reach the brain, leading to total blindness in that eye.
Additionally, if the optic chiasm or any other parts of the visual pathway were affected, it could lead to other types of vision loss, such as partial loss of the visual field. However, since the problem here is the complete destruction of the left optic nerve, the most direct consequence is complete blindness in the left eye. There is no crossing of visual fibers from the left eye to the right brain hemisphere; thus, there will not be any effect on the right visual field or vision in the right eye.
To summarize, the complete loss of vision in the left eye occurs because the optic nerve, which is the direct pathway for visual information from that eye, has been destroyed.