MCAT Behavioral Sciences Question 30: Answer and Explanation

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Question: 30

15. A patient comes in with a tumor of the pituitary gland, which grows upwards into the optic chiasm and causes a visual field defect. The most likely defect from compression of the optic chiasm is:

  • A. complete blindness in one eye.
  • B. loss of the upper visual fields in both eyes.
  • C. loss of the nasal visual fields in both eyes.
  • D. loss of the temporal visual fields in both eyes.

Correct Answer: D

Explanation:

The optic chiasm houses the crossing fibers from each optic nerve. Specifically, the fibers coming from the nasal half of the retina in each eye cross in the chiasm to join the optic tract on the opposite side. Remember that the lens of the eye causes inversion, so images on the nasal half of the retina actually originate in the temporal visual field. This condition is called bitemporal hemianopsia.

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