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Retention of macular function in spite of losses in the adjacent visual field as, for example, in homonymous hemianopia due to a cortical lesion (e.g. an interference in the blood flow in the middle cerebral artery). This is due to the fact that most cortical lesions are not large enough to affect the whole extensive cortical area representing the macula, thus leaving some of the area unaffected. See cortical magnification.