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Pupillary size as determined by oculomotor nerve function is a most useful indicator of an expanding intracranial lesion. The pupil dilates on the side of the expanding lesion and may reveal an impaired or absent reaction to light. Further, increasing intracranial pressure may produce a bilateral III nerve palsy.
Optic nerve dysfunction is important to record, but it has less value as an indicator of the progress of a lesion.