Amplitude Of Pupillary Response Research Articles

Influence of transcranial magnetic stimulation on pupil size

In 22 healthy subjects, painless repetitive transcranial magnetic stimulation (rTMS) was used to investigate the role of the cortex in the regulation of pupil size and the influence of TMS on the central autonomic nervous system. RTMS was performed over three brain regions of each hemisphere (frontal, central, parieto-occipital), over cervical nerve roots and in front of the ear (sham stimulation) while the size of the pupil was measured by infrared oculography. rTMS always elicited a dilatation of both pupils, with its maximum after approximately 1.5 s and without significant R–L difference in latency or amplitude of pupillary response. No differential effects were observed for stimulation over different cortex regions of one hemisphere, but stimulation over the right central region evoked a larger dilatation of the pupil than stimulation over the left. Pupillary dilatation was larger for cervical nerve root stimulation (+13.2±8.3% (S.D.) of baseline) than for suprathreshold cortex stimulation (+8.4±4.5%, five 10-Hz stimuli). Pupillary dilatation in response to magnetic cortex stimulation appears to reflect a mainly unspecific activation of the sympathetic system rather than an activation of a cortical pupillomotor centre. Sympathetic activation following rTMS of the cortex does not limit its experimental and therapeutic application.

Pupillography of a Relative Afferent Pupillary Defect

The pupillary reactions during the alternating light test of Levatin consist of bilateral pupillary constriction followed by redilatation each time the light moves from one eye to the other. The pupils constrict less and redilate more in an eye with an optic nerve lesion than in the unaffected fellow eye. The amplitude of pupillary responses and the average pupil size decrease when the light is alternated more rapidly. Placing neutral density filters over the better eye has the effect of decreasing the amplitude of pupillary responses when that eye is stimulated while increasing responses of the diseased eye. Because of contraction anisocoria and physiologic anisocoria, the most reliable pupillographic and clinical criterion for diagnosing a relative afferent pupillary defect using the alternating light test is an initial pupillary constriction in the suspected eye that is smaller with direct than with consensual stimulation.