Interactions between photic drive responses and multifocal pupillography in epilepsy

Abstract

Purpose : Photic drive responses (PDRs) have been used to explore cortical hyper-excitability in neurological disorders. We quantified changes PDR in epilepsy patients and looked for interactions with responses obtained from multifocal objective pupillographic perimetry (mfPOP).

Methods : This was a cross-sectional study of 15 consecutive epilepsy patients (8 males; mean age ± SD 47.3 ± 4.6 years), and 15 controls (9 males; mean age 52.7 ± 4.6 years) undergoing routine EEG with standard intermittent photic stimulation (IPS) and testing with the mfPOP device. EEG spectral amplitudes during IPS were obtained using the Fourier transform. N-fold changes in PDR (expressed in dB) when IPS and alpha bands overlapped, the alpha-band gain, were examined and also their interaction with mfPOP responses. Alpha-band gain was determined by comparing eyes-open and eyes–closed conditions. mfPOP responses were obtained from 44 regions/visual field. Response time-to-peak and standardized amplitude was recorded for each test region.

Results : A linear model showed that an epileptic attack within 1 month increased the alpha-band gain by 1.33 dB (p=0.01). Generalised epilepsy (i.e. no focal epilepsy) decreased the alpha-band gain by 1.03 dB (p=0.03). For each decade increase in age the gain increased by 0.36 dB (p=0.007). For every 1 dB increase in alpha band gain pupil responses were reduced by 0.207 ± 0.09 dB on average across the field (p=0.024).

Conclusions : Investigating alpha-band gain offers another way to quantify cortical hyper-excitability in epilepsy patients. Responses to mfPOP may provide less invasive means to quantify hyper-excitability.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.