Altered pupillary responses in photosensitive patients and their relationship to measures of brain activity

Abstract

 

Purposes: Photosensitive individuals show an increased sensitivity to photic stimulation that can lead in severe cases to absence seizures. The excitatory nature of the light stimulus in photosenstivity is dependent on color and frequency parameters (Takahashi & Tsukahara, 1976). We previously found a similar color and frequency dependence on equiluminant flicker in inducing pupillary constrictions in non-photosensitive observers (Drew et al., 2000). Here we examine whether the pupillary constriction in two photosenstive observers in response to full-field color flicker is deviated from that of non-photosensitive controls. Methods: Observers were 12 and 13-year old females (RS and RN, respectively) who had a prior history of photosensitivity. Both observers viewed full-field flickers of differing colors and frequencies. Video pupillometry and electroencephalographic data (EEG) were obtained. Prior to testing, observer RS was treated with sodium valproate to prevent a photoconvulsive response during testing. Results: the pupillary responses of both observers was significantly altered from that of non-photosensitive observers, although in different directions. RS (treated) had significantly larger than average constrictions in response to flicker, RN (untreated) smaller. The color-dependency of flicker was altered from non-photosensitive observers. Preliminary analysis also indicates a correlation between the size of pupillary constriction in patients and the amount of rhythmicity in the EEG. Discussion: The different sizes of responses in patients may be the result of sodium valproate administration in one but not the other observer. The overall pupillary response may be indicative of gain control mechanisms in response to excitatory stimuli, which may be altered in photosenstitive patients.