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A.E. Gallagher, X. Zhang, V.C. Greenstein, D.C. Hood; An Evaluation of the Multifocal Visual Evoked Potential (mfVEP) Obtained with Dichoptic Testing . Invest. Ophthalmol. Vis. Sci. 2003;44(13):4109.
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Purpose: To evaluate the utility of dichoptic multifocal visual evoked potential (mfVEP) testing. Methods: Dichoptic and monocular pattern-reversal mfVEPs were recorded from 5 subjects with no known visual abnormalities. All 5 subjects were right eye dominant. The display contained two 48-sector dartboard arrays, each with a radius of 14.3° and was produced with VERIS 5.x (EDI). The arrays were comparable to the five inner rings of the standard Dart Board 60 With Pattern display in VERIS. For dichoptic testing, the display was viewed through a stereoscope built with base-out prisms and a septum. mfVEPs were recorded while the subject maintained fusion of the two monocular displays. For monocular testing, one eye and the associated display were occluded. The records were amplified with cutoffs at 3 and 100 Hz and filtered offline with a FFT lowpass filter (35 Hz) [1,2]. For each dichoptic or monocular test, one 14-minute recording was obtained with electrodes placed at the inion (reference) and 4 cm above it (active). For each subject and each condition, a signal-to-noise ratio (SNR) was determined for each of the 48 responses by dividing the root mean square (RMS) of a signal window (45 to 150 ms) by the mean RMS of the 48-noise windows (325 to 430 ms). Results: For the right eye, the mean SNRs were 3.1 (dichoptic test) and 3.6 (monocular). For the left eye, the mean SNRs were 2.9 (dichoptic test) and 3.6 (monocular). The average ratio of the RMS amplitudes of the two eyes showed about the same variability for the monocular tests (SD=1.34) as compared to the dichoptic test (SD=1.33). Conclusions: When compared to separate monocular tests, the dichoptic test has the advantage of decreasing recording time by 50%, and thus, theoretically increasing the SNR by about a factor of 1.4 for the same total recording time. However, the monocular mfVEP SNR was about 1.2 times larger than the dichoptic mfVEP, eliminating most of this potential advantage. Further, recording from both eyes at once did not decrease the variability of the interocular comparison. Given the technical difficulties involved in obtaining fusion, it is not clear that the dichoptic mfVEP will be of value in the clinic. 1. Hood et al (2002) AO. 2. Hood & Greenstein (2003) Prog Ret Eye Res. 3. Zhang et al (2002) Doc Ophth.
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