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DC Hood, CS Chen, VC Greenstien, JE Hong, JM Liebmann, JG Odel, P Thienprasiddhi, R Ritch, X Zhang; A Comparison of Visual Field Defects and Multifocal Visual Evoked Potentials: Evidence for a Linear Relationship . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3900.
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Purpose: To determine the relationship between spatially localized visual evoked potentials (mfVEP) and behaviorally determined visual fields. Method: Patients had ischemic optic neuropathy (ION) (n=9) or open-angle glaucoma (n=8) and had unilateral defects as determined by 24-2 Humphrey Visual Fields (HVF). Monocular mfVEPs were obtained from each eye using a pattern-reversal dartboard array with 60 sectors; the entire display was 44.5 deg. in diameter. The four recording electrodes were placed at the inion (I) and I+4 cm, and also at two lateral locations up 1 cm and over 4 cm. A root-mean-square (RMS) amplitude and signal-to-noise-ratio (SNR) were obtained for each response from the 6 possible channels (three recorded and three derived) [1,2]. Both the midline channel and the best channel were analyzed. Estimates of visual field changes in the 60 sectors of the mfVEP array were interpolated from the visual fields . Results: Monocular mfVEP amplitude (RMS or SNR) of the affected eye fell off rapidly with HVF loss in dB. For regions with HVF losses of 15 dB or more, little or no signal could be detected. The correlation between mfVEP amplitude and HVF loss was not good (r<0.4) as small signals were not uniquely associated with poor fields. However, the interocular mfVEP ratio, obtained as RMS(OD)/RMS(OS) for each pair of responses [1,3], correlated well with the difference between the HVF values of the two eyes (r between 0.7 and 0.9 depending upon the SNR). A model that assumes a linear relationship between the decrease in mfVEP amplitude and the loss in HVF sensitivity (linear scale) describes the data. Conclusion: While interocular mfVEP comparisons can detect local defects [1,4], the monocular mfVEP has very poor specificity. The fit of the model suggests that the decrease in the mfVEP signal is proportional to the loss of HVF sensitivity (linear not dB scale). A simple way for this to occur would be if both were proportional to the percentage of ganglion cells lost. 1. Hood et al (2000), IOVS 2. Zhang et al, (in press) DOOP 3. Hood & Zhang (2000) DOOP 4. Graham et al (2000), JG.
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