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X. Zhang, J. C. Park, M. Wang, D. C. Hood; A Method for Simultaneously Obtaining Behavioral Thresholds and Multifocal Visual Evoked Potentials (mfVEP). Invest. Ophthalmol. Vis. Sci. 2008;49(13):723. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To introduce a method that allows for simultaneous measurement of multifocal visual evoked potentials ( mfVEP) and behavioral visual field thresholds. Both local VEP and visual field thresholds are important for clinical diagnoses and non-clinical research. Currently, these are measured separately with different displays.
The proposed method measures the local VEP using a contrast reversing checker board and local contrast discrimination threshold for the same stimulus. A standard, 60 sector, black and white reversing, checkerboard stimulus of 32% contrast was presented monocularly. At random times, one of the sectors was incremented with yellow/blue contrast for 106ms. The subject pressed a key when s/he detected a color change. Fixation was controlled with a central cross. A staircase method with 0.63 dB steps and a dynamic range from 1% to 78% contrast (19dB) was used to determine contrast threshold. Three normal subjects with visual acuity >=20/20 and normal color vision participated in the study. For both the left and right eyes, 7-minute mfVEP recordings were obtained with and without the blue/yellow behavioral task.
Both the waveform and amplitude of the mfVEP were identical when obtained with or without the behavioral task. The average difference of the signal to noise ratio was 0.06 dB. For all 60 traces and all 3 subjects, the mean of the interocular ratio of the behavioral thresholds was 0.28 and the standard deviation was 1.88 dB. For both eyes and all 60 traces, the range of thresholds was 2.15 dB across the three subjects. The blue/yellow contrast thresholds were consistent between the two eyes and across subjects. All subjects showed a threshold elevation within the central 2.5 degrees, a characteristic of the short wavelength cone system.
A behavioral contrast discrimination task can be performed during the measurement of mfVEPs and this task does not affect the the mfVEP recordings.
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