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R Yagev, CA Westall, M Banh, E Mezer, G Mirabella, RJ Buncic; Contrast Sensitivity with Sweep VEP in Patients with Optic Pathway Gliomas and Normal Visual Acuity . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1808.
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Purpose: To investigate the use of sweep visual evoked potentials (SVEPs) in determining contrast sensitivity in children with optic pathway gliomas (OPG) with normal visual acuity. Current methods of diagnosing OPG - magnetic resonance imaging (MRI) and computer tomography (CT) - are expensive and require sedation. Moreover, in the case of CT there is associated radiation exposure. Therefore, the NIH recommendation is not to perform these screening examinations on high-risk populations (neurofibromatosis patients), unless clinical signs exist. Buncic and colleagues have shown previously that patients with OPG exhibit reduced contrast sensitivities. SVEPs provide an objective measurement of contrast sensitivity that is used successfully in infants and young children. Hence, we assessed contrast sensitivity with SVEPs in patients with OPG. Methods: Children with OPG (n=16) with visual acuity of 20/30 or better and control subjects (n=16) were tested using SVEPs, with recording according to the International 10-20 System. A contrast sensitivity function was fit to obtained thresholds for three contrast sweeps and two spatial frequency sweeps using a negative exponential model. From this model, log maximum sensitivity was compared between the groups. Signals were sampled at 600Hz, amplified by 50000 times, and averaged over all trials for each of the five conditions. Results: Patients with OPG displayed reduced contrast sensitivity, compared with normal controls (mean log contrast sensitivity = 1.73 versus 2.03, p<0.030). Conclusion: Some children with OPG have reduced contrast sensitivity when assessed using the SVEP. Thus, SVEP can provide a useful measure of visual pathway function in infants and children with neurofibromatosis and may be used to track visual function in these patients over time.
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