Contrast-Processing Dysfunction in both Magnocellular and Parvocellular Pathways in Migraineurs with or without aura

PURPOSE. To assess contrast-discrimination thresholds in patients with migraine who have manifest visual field loss. This study was undertaken to determine whether contrast processingabnormalities in migraineurs are more readily identified byusing stimuli that elicit a response from the subject that depends,at least in part, on adaptation mechanisms, and if so, whether deficits appear more pronounced in magnocellular (M) or parvocellular (P) visual pathways.METHODS. Ten patients with migraine who had abnormal visualfields measured with flicker perimetry but had normal standardautomated perimetry (SAP) thresholds participated, along with15 age-matched control subjects. Contrast-discrimination performancewas assessed with the steady-pedestal (magnocellular)and pulsed-pedestal (parvocellular) stimuli of Pokorny andSmith for seven pedestal luminances between 15 and 60 cd/m2on a background of 30 cd/m2. Subjects were tested foveallyand midperipherally at 12.5°. Migraineurs were tested in thequadrant of worst visual field performance. Control subjectswere assessed in locations matched to those of the migrainegroup. RESULTS. Foveal performance was not significantly differentbetween the migraine and control groups for either task. At12.5° the migraine group had significantly raised thresholds forboth conditions. Effect size statistics revealed similar deficitmagnitudes for each test (steady pedestal, 1.06; pulsed pedestal, 1.04). CONCLUSIONS. Dysfunction in both the M and P pathways wasidentified in the midperipheral visual field of the migrainegroup. The P pathway dysfunction was not identified by SAP.These findings support the possibility of nonselective neuraladaptation abnormalities in some subjects with migraine.