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J.P. Kelly, A. Weiss; Objective VEP Analysis and Field Defects in Children With Optic Pathway Tumors . Invest. Ophthalmol. Vis. Sci. 2003;44(13):2714.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Hemianopic field defects can produce hemispheric asymmetry in the VEP amplitude. However, detection of a field defect by VEP asymmetry is limited by reduced amplitudes and abnormal waveforms. We examined whether objective analysis of the VEP improves detection of a field defect in children with optic pathway tumors. Methods: Patients were 19 children (34 eyes) with suprasellar tumors involving the optic nerve/chiasm, and tracts on MRI (11 chiasmal glioma, 8 craniopharyngioma). All patients had Goldmann visual fields and 5 patients were also tested by Humphrey perimetry. Control data was from 22 eyes of 13 children. Active sites were O3, Oz, and O4 referenced to Cz. Stimuli were check reversal (163', 84', 42', 18') and sinewave grating onset (0.5 cy/deg -- achromatic, L-M, and S-cone color axes). Amplitude was to the major peak near 100-160 msec. Objective analysis of the VEP used modified T2circ. Each EEG epoch was decomposed into sine and cosine coefficients by DFT. A signal-to-noise ratio (S/N) at each frequency was defined as the average magnitude divided by the radius of the 95% confidence circle of the scatter of sine and cosine components. Results: The main finding was that patients had a reduction in both amplitude and peak S/N ratio at the midline, which was more reduced in patients with a field defect. Although VEP amplitude asymmetries occurred in individual subjects, on average there was no consistent hemispheric asymmetry (in amplitudes or peak S/N ratios) between subjects with or without a field defect. When only the midline recording was analyzed, detection of a visual field defect was greatly improved by using S/N ratios compared to VEP amplitudes. Sensitivity/specificity for peak S/N ratio ranged from 0.76/1.0 for achromatic gratings to 0.62/0.97 for L-M chromatic gratings. Sensitivity/specificity for VEP amplitudes was always less than 0.50/0.75. Conclusions: VEP asymmetry was not consistently found in children with a hemianopic field defect probably due to overall low S/N ratios. Objective S/N analysis improved detection of a field defect relative to VEP amplitudes. A combination of optic nerve dysfunction and visual field loss may contribute to the S/N reduction at the midline.
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