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Correct! You are looking at a temporal visual field defect in the left eye that has a discrete border aligned to the vertical meridian that passes through fixation. The visual field in the right eye is normal. The localizing feature here is that the visual field defect has a border aligned to the vertical meridian, which places the lesion in the left optic nerve as it approaches the optic chiasm. At that junction, axons derived from nasal retina have split off from those derived from temporal retina. Lesions there—no matter their nature—will preferentially damage the nasal axons to produce this unilateral temporal hemianopic visual field defect. If the lesion were situated farther posterior toward the optic chiasm, a temporal visual field defect would also be present in the other eye--a bitemporal hemianopia. This patient had a meningioma growing off the left clinoid process

Surgical removal led to normalization of the visual fields and disappearance of the afferent pupil defect. Early diagnosis—before the tumor has exerted severe compression of the optic pathway—is critical to the visual outcome in this circumstance. Many patients show unilateral temporal hemianopic defects on formal perimetry. How would you know that the defect reflects disease in the ipsilateral optic nerve near its junction with the optic chiasm? By finding an ipsilateral afferent pupil defect, as in this case.

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Incorrect