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A 72 year old man noticed a stable defect in the vision of his left eye of uncertain duration. He made visits to an optometrist and ophthalmologist, which consistently disclosed normal visual acuities, pupillary reflexes, confrontation visual fields, clear ocular media, and normal-appearing retinas and optic discs. Eventually this visual field examination result emerged.
Where is the lesion?
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Correct!
Notice three features of these visual field defects: 1) confined to the left hemifields in both eyes; 2) have discrete borders along the vertical meridian; 3) spare the central 10 degrees of the visual fields. These
features define a “macular-sparing homonymous hemianopia,” one of the most localizing of all visual field defects! This pattern always derives from a lesion in the visual cortex that spares the posterior portion of
that cortex, the termination point of axons carrying visual information from the central 10 degrees of the visual field.
The patient was slow to notice these defects because of macular sparing, which allowed him to read at nearly normal speed and to ignore the more peripheral scotomas. He thought he could drive safely.
However, in most jurisdictions, the finding of macular-sparing homonymous hemianopia would preclude a patient from being issued a driving license! The cause of these defects was an ischemic stroke in the
distribution of the right posterior cerebral artery.
The defects are permanent. He had atrial fibrillation and required long term rate control and anticoagulation to prevent
future stroke.