Incorrect

Incorrect

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Correct! These small defects in the left hemifields are confined to the central degrees of the visual field. They are called “homonymous hemianopic paracentral scotomas.” Because they lie so close to the fixation point, they cause troublesome visual symptoms. They slow reading speed, as the patient consistently misses the first part of each word. You will be surprised to discover that the lesion occupied the entire back half of the visual cortex on the right side! Why would such a large lesion cause such small defects? Because the human brain devotes the entire posterior half of visual cortex to the central 10 degrees of the visual field, a phenomenon called the “magnification factor.” It testifies to the importance of “foveal vision” in primates. Such paracentral defects are routinely overlooked on standard static perimetry protocols, in which the test points are spaced far enough apart (“6 degrees of separation”) to miss the defects. Protocols that sample the central 10 degrees with test points at closer intervals are more likely to find these defects. In this patient, the defects were caused by posterior cerebral artery infarction, possibly related to embolism during the heart surgery.