Using Multifocal Steady-State Visual Evoked Potentials for Objective Assessment of Visual Field Loss in Glaucoma

Abstract

 

Purpose

 

This study aimed to develop an electroencephalogram (EEG)-based brain sensing technique for objective assessment of visual field defects in glaucoma using multifocal steady-state visual-evoked potentials (mfSSVEPs).

 

Methods

 

This study hypothesized that while presenting multiple frequency-tagged flickering sectors (alternating black/white) in the monocular visual field, a sector(s) corresponding to a visual field deficit(s) would be less perceivable or unperceivable and thereby would lead to weaker SSVEP amplitude with stronger inter-trial variability, compared to healthy spots. To test the hypothesis, we designed a layout of visual stimuli consisting of 20 sectors in three concentric rings (subtending 6^°, 15^°, and 25^° in the visual field) for eliciting mfSSVEPs. All sectors flickered concurrently at frequencies from 8 to 11.8 Hz with a step of 0.2 Hz. MfSSVEPs from 14 patients with asymmetric glaucomatous visual field defects on standard automated perimetry (SAP) were recorded while their monocular visual fields were exposed to the stimulation (5 seconds per trial, 100 trials per eye). We evaluated the relationship between asymmetry in visual field sensitivity (in 1/L scale) and mfSSVEP asymmetries (amplitude and inter-trial variability).

 

Results

 

SAP sensitivity asymmetry was positively correlated with mfSSVEP amplitude asymmetry (Figure A) but negatively related to the mfSSVEP variability asymmetry (Figure B). The obtained multivariable model containing mfSSVEP amplitude and inter-trial variability had an R² of 70% for explaining SAP results (p < 0.001).

 

Conclusions

 

This study demonstrated that the mfSSVEP dynamics in terms of amplitude and inter-trial variability are capable of serving as objective biomarkers to assess visual field loss in glaucoma.  

 

Figure. Results of mfSSVEP in 14 subjects with asymmetric glaucoma. Relationships between SAP sensitivity asymmetry versus (A) mfSSVEP amplitude asymmetry and versus (B) mfSSVEP inter-trial variability asymmetry.