Abstract
Aims: Flickering light is strongly aversive to many individuals with migraine. This study was designed to evaluate other abnormalities in the processing of temporally modulating visual stimulation.Methods: We measured psychophysical thresholds for detection of a flickering target and for the discrimination of suprathreshold flicker contrasts (increment thresholds) in 14 migraineurs and 14 healthy controls with and without prior adaptation to high-contrast flicker. Visual discomfort (aversion) thresholds were also assessed.Results: In the baseline (no adaptation) conditions, detection and discrimination thresholds did not differ significantly between groups. Following adaptation, flicker detection thresholds were elevated equivalently in both groups; however, discrimination thresholds were more strongly affected in migraineurs than in controls, showing greater elevation at moderate contrasts and greater threshold reduction (sensitisation) at high contrast (70%). Migraineurs also had significantly elevated discomfort scores, and these were significantly correlated with number of years with migraine.Discussion: We conclude that visual flicker not only causes discomfort but also exerts measurable effects on contrast processing in the visual pathways in migraine. The findings are discussed in the context of the existing literature on habituation, adaptation and contrast-gain control.
Highlights
Photophobia or aversion to light is one of the defining characteristics of migraine headache [1]
This provides quantitative support for the common anecdotal reports from migraineurs that they are bothered by a wide range of flickering patterns from fluorescent lights and television screens to sunlight viewed through trees from a moving automobile
These findings may be summarized in three points. (i) Detection thresholds (0% base contrast) did not differ between migraineurs and HCs, and the groups showed equivalent elevations in contrast detection thresholds following adaptation to high-contrast flicker. (ii) Baseline discrimination thresholds did not differ significantly between migraineurs and controls; there was a slight trend toward lower thresholds in migraineurs at both contrasts tested. (iii) Adaptation to 70%-contrast flicker significantly elevated contrast discrimination thresholds at moderate contrast (10%) and significantly lowered discrimination thresholds at high contrast (70%) in migraineurs
Summary
Photophobia or aversion to light is one of the defining characteristics of migraine headache [1]. This is most intense during the headache phase, many migraineurs report heightened visual sensitivity between migraine episodes [2,3], and as a prodromal symptom as well [4]. In addition to finding normal levels of illumination too bright or even painful, specific spatial and temporal patterning of light have been reported to be aversive. Controlled investigations of this phenomenon have focused largely on its spatial properties. The term pattern glare has been coined for these spatial phenomena, and interictal pattern glare has been reported to be correlated with performance on certain other visual tasks [3,7]
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