Binocular Multifocal VEP Using Virtual Reality Goggles Enhances Inter-Eye Asymmetry and Improves Detection of Early Glaucoma

Abstract

Purpose:: Multifocal visual evoked potential (mfVEP) recording is a sensitive method for detection of optic neuropathy in glaucoma and optic neuritis. The current technique involves monocular recording. We recently demonstrated that simultaneous (dichoptic) recording of both eyes is possible using virtual reality goggles. This, however, resulted in a degree of binocular cortical suppression (10-20%) and subsequent amplitude reduction. We hypothesized that in early unilateral visual field loss release of binocular neurons from suppression by reduced input from affected eye may enhance inter-eye asymmetry and result in earlier detection of abnormality.

Methods:: . MfVEP was recorded using the AccuMap^TM system. Simultaneous stimulation of both eyes was performed using virtual reality goggles and a sparse stimulus paradigm. Multiple areas of visual field extending to 18° of eccentricity were stimulated using a cortically scaled pattern which appeared according to pseudorandom sequence. Both monocular and binocular stimulation were implemented on the same day in random order. 25 glaucoma patients with unilateral visual field defect were tested. Amplitude and asymmetry coefficients were calculated for each area of the visual field and compared to a normals (30 subjects).

Results:: Based on the combination of amplitude deviation and asymmetry all visual field defects were detected using both monocular and binocular stimulation. When abnormal hemifields were analysed, inter-eye asymmetry was larger on binocular recording compared to monocular (averaged asymmetry coefficient 0.46 vs 0.35, p=0.01, paired t-test). There were also 6 additional hemifields identified as abnormal on binocular recording when compared to Humphrey visual field and monocular mfVEP. In all 6 eyes optic disc rim thinning corresponding to the abnormal hemifield was noted. In contrast the normals showed less inter-eye asymmetry on binocular than monocular sequential testing.

Conclusions:: Using binocular mfVEP stimulation may result in potential early detection of glaucoma due to enhanced inter-ocular asymmetry.

Keywords: electrophysiology: clinical • visual fields