Objective Dynamic Visual Acuity Assessment Method Based on Steady-State Visual Evoked Potentials with Smooth-Pursuit Eye Movements Recording

Abstract

Dynamic visual acuity (DVA) is a measurement of the ability to discriminate critical details of relative moving objects. It is regarded as a superior observation index that can reflect the comprehensive functional state of a vision system. However, there is still not a gold criterion for DVA assessment in the clinical test. Recently, steady-state visual evoked potential (SSVEP) is proved as an objective, quantitative and sensitive method of evaluating objective visual acuity. By recording and analyzing SSVEP signals and eye movements, a new approach to assess DVA levels can also be provided. In this study, we designed a special paradigm to induce EEG and eye movement signals simultaneously. A checkerboard flips in the background at 7.5 Hz, while the visible part of a mask makes a circular motion, which is stable in stimulation and convenient for programming. The spatial frequencies of checkerboard optotypes were designed into ten levels, corresponding to the minimum angle of resolution of 1′ to 10′. The visible part was 10° to the subjects, and its velocity was set at two speeds (20°/s and 40°/s). The empirical mode decomposition (EMD), canonical correlation analysis (CCA), and some statistical methods were used in signal processing. The frequency feature of the SSVEP signals was calculated to reflect DVA levels. The standard error (SE) of eye movements was used as the test's reliability index to prevent ineffective eye tracking movements. The result of the proposed objective method was compared with a traditional subjective method, e.g., DinVA 3.0. The objective and subjective visual acuity of fifteen healthy adults were tested at both speeds. It was confirmed that their results were correlated significantly. Our study proved that SSVEP is an objective and quantitative method to measure dynamic visual acuity. The combination of eye movements and EEG signals is feasible and shows excellent potential.