After having a brain tumor, a patient's left optic tract is damaged. Which of the following areas would present with vision loss?

Question

After having a brain tumor, a patient's left optic tract is damaged. Which of the following areas would present with vision loss?

BlackTom AI · Accepted Answer

Left optic tract damage produces a right homonymous hemianopia — loss of the right visual field in both eyes.

Relevant concepts:
- Each visual field is represented on the contralateral cerebral hemisphere after the optic chiasm.
- Nasal retinal fibers (from the medial retina) cross at the optic chiasm; temporal retinal fibers remain uncrossed.
- After the chiasm, each optic tract contains fibers representing the opposite (contralateral) visual field from both eyes.

Step-by-step reasoning:
1. Take a stimulus in the right visual field. This stimulus projects to the nasal retina of the right eye and to the temporal retina of the left eye.
2. Nasal retinal fibers cross at the optic chiasm. Thus the signal from the nasal retina of the right eye crosses to the left side.
3. Temporal retinal fibers do not cross. The temporal retina of the left eye sends its signal directly to the left side.
4. Therefore, both contributions (right-eye nasal + left-eye temporal) travel in the left optic tract to the left lateral geniculate nucleus and visual cortex.
5. If the left optic tract is damaged, these fibers carrying the right visual field are lost, producing right homonymous hemianopia (loss of right visual field in both eyes).

Why the correct answer is correct:
- The left optic tract carries fibers that represent the right visual field from both eyes; damaging it removes perception of that entire right visual field.

Why the other options are incorrect:
- Part of both right and left visual fields: too vague and not specific — a unilateral optic tract lesion causes loss of one entire visual field (contralateral), not scattered parts of both fields.
- All vision: would require bilateral optic nerve/tract or cortical damage, not unilateral tract damage.
- Peripheral vision: peripheral (tunnel) loss is not the pattern of an optic tract lesion; optic tract lesions cause homonymous field loss, not only peripheral loss.
- Left visual field: incorrect side — a left optic tract lesion affects the right visual field, not the left.

Conclusion: Damage to the left optic tract produces loss of the right visual field. Final answer: Right visual field.

After having a brain tumor, a patient's left optic tract is damaged. Which of the following areas would present with vision loss?单项选择题

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