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B Fortune, DC Hood, CA Johnson; Comparison of Conventional and Multifocal VEPs . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2126.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To compare conventional visual evoked potentials (CVEPs) with multifocal (mf) VEPs. Methods: mfVEPs were recorded in 12 normal and 6 selected glaucomatous subjects with an active electrode at Oz (∼3.5 cm above the inion), referenced to the inion (bipolar, BP) or to Fz (monopolar, MP). Signals were filtered 3-100 Hz. The mfVEP stimulus (Dart Board 60 With Pattern, VERIS, EDI) had a mean luminance of 100 cd/m^2 and a diameter of 44.5 deg. CVEPs were recorded during the same session using an LKC system (Utas-E3000). The checkerboard stimulus subtended 28 x 21 deg, had a mean luminance of 75 cd/m^2 and contrast of 90%. Transient pattern reversal responses (2.5 Hz) were recorded for check sizes ranging from 0.2-0.825 deg. Signals were filtered 1-100 Hz. White illuminated cardboard masks were used to isolate upper and lower hemifields for the whole screen, the central 5 deg, a 5 to 20 deg annulus, and an area corresponding to one of the 60 mfVEP stimuli. Results: All normal subjects showed dramatic asymmetries between hemifield responses for MP CVEPs. Upper field responses had the same polarity but were much smaller than lower field responses for the whole stimulus, as well as for isolated central and annular areas. For 9 of 12 subjects, BP records were similar to MP but smaller; while in 3 there was a polarity reversal between hemifields. For mfVEPs, there was much better amplitude symmetry across the horizontal midline, with a polarity reversal occurring in all subjects for both BP and MP. Signal-to-noise ratio was better for BP than MP in ≷85% of all mfVEP records. CVEP and mfVEP waveforms were fundamentally different, even for small isolated areas. Evidence of response suppression was observed in all subjects for CVEPs (sum of parts ≷ full field response). In contrast, isolation of mf stimulus elements revealed little evidence for spatial interactions in the standard mfVEPs. In subjects with glaucoma, even severe visual field (VF) loss, if limited to the superior VF, was undetectable using CVEPs yet easily detected by the mfVEP. Conclusion: Full-field CVEPs are not simply the sum of responses to smaller parts of the stimulus, nor can they be simply related to mfVEPs. The differences between C and mfVEPs most likely derive from the differences in temporal stimulus properties and the relative presence of temporal and/or spatial interactions. mfVEPs offer a substantial improvement for objective detection of glaucomatous dysfunction, especially for the superior visual field. Support: MJ Murdock Charitable Trust; NIH: EY03424 (CAJ), EY02115 (DCH)
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