Eyetracking-enhanced VEP for nystagmus

Purpose : Visual evoked potential (VEP) testing is an essential first stage in the diagnostic workup of patients with infantile nystagmus (IN). VEPs are an important factor in the diagnosis of albinism, which accompanies IN in ~28% of cases, as well as chiasmal, optic nerve and neurometabolic disease that can all present with IN. VEPs are also used to assess prognostic visual ability in cases of retinal dystrophy and optic nerve disease. Despite being used regularly in those with IN, VEP testing requires patients to keep the eyes still; something that people with IN naturally cannot do. Fixation instability during VEP testing is believed to reduce VEP signal amplitude, and as a result, the reliability of VEP may be reduced in one of the patient groups that needs it the most. This study investigates whether VEP signal quality (amplitude) can be improved in people with IN, by triggering acquisition only during the foveating (slow) periods of the nystagmus waveform. Methods : A novel method of VEP triggering was developed, by recording live eye movements from individuals with IN (using an EyeLink 1000+), and triggering VEP acquisition (with an Espion device) only during foveating periods of the nystagmus waveform (i.e., low velocity). VEP amplitude as acquired using this method was compared to VEPs triggered using continuous (regular, non-gaze-contingent) acquisition. Data were collected in six patients with IN (pattern onset/offset in all participants, and pattern reversal in four). Further data collection is underway and will be reported in full at the meeting. Results : VEP signal amplitude is significantly increased by gaze-contingent VEP triggering (mean = 12 µV, as compared to 9 µV under continuous acquisition; p = 0.03). Conclusions : Triggering VEP acquisition during foveation periods significantly increases the VEP amplitude and therefore has the potential to improve prognostic reliability in people with IN.