Electroretinography and pupillary response in migraine

OBJECTIVE: To compare rod, cone, and retinal ganglion function with pupillary response in the same migraine and headache-free individuals. BACKGROUND: Migraine is associated with a sensitivity to the visual environment, including light, stripes, and color, but the biological causes are still heavily debated. One of the potential sources of this sensitivity is abnormal functioning in the retina. Typically, electroretinography (ERG) assessments require dilated pupils to achieve the desired retinal illuminance. However, abnormal pupillary functioning has been linked with migraine, and so artificially dilating the pupil may obscure the effects of migraine on retinal activity. METHODS: Here, we compared rod, cone, and the photopic negative-response (to assess retinal ganglion functioning) ERG activity using the RETeval that delivered standard International Society for Clinical Electrophysiology of Vision protocols in 35 individuals with migraine and 25 headache-free individuals. To avoid dilating the pupils, the luminance of the stimuli was continuously adjusted for pupil diameter to hold retinal illumination constant. This allowed for pupil diameter to be measured simultaneously. RESULTS: ERG response amplitudes and timings were similar across migraine and headache-free groups for all protocols, except for a smaller a-wave amplitude in the migraine group in response to the light-adapted slow light flashes. We also found larger pupil diameters in the migraine group, particularly for the dark-adapted protocols, and larger pupils correlated with faster ERG responses to the light-adapted flicker. CONCLUSIONS: Together, this suggests that pupil functioning is abnormal in migraine, particularly under specific lighting conditions, and may be linked to a hyper-response to uncomfortable flicker in migraine.