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Diana Ludlam, Naveen Yadav, Kenneth Ciuffreda; Effect of Simulated Octant Visual Field Defects on the Visual-Evoked Potential (VEP). Invest. Ophthalmol. Vis. Sci. 2013;54(15):6144. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To assess the effect of simulated small rectangular octant (i.e., one-eighth of the test field) visual-field defects on the visual-evoked potential (VEP) amplitude in the visually-normal (VN) adult population.
Five VN adults (ages 19-70 years) participated in the study. Conventional full-field (FF) VEP testing was employed using the DIOPSYS NOVA-TR system (17 H x 15 V degrees stimulus size, 64X64 check size, 64 cd/meter square, 1 Hz temporal frequency, 85% contrast, binocular viewing with spectacle correction). FF checkerboard pattern (17H X 15V degrees) VEP responses were tested and compared binocularly at 1m to the following two simulated horizontally-oriented, octant (7.5H X 3.75V degrees) visual-field defects: 1) 1/8th non-patterned octant stimuli (7.5H X 3.75V degrees), i.e., 1 of the 8 regions of the FF checkerboard pattern was non-patterned (i.e., blank) (Fig. 1), while the other 7 octants contained the checkerboard stimuli, and 2) 1/8th patterned octant stimuli, i.e., 1 of the 8 regions of the FF checkerboard pattern was present, while the other 7 octants were non-patterned (i.e., blank) (Fig. 2). The average of 4 trials was used for the analysis. Each trial duration was 90 seconds. Octant location was randomized.
Two repeated-measures, one-way ANOVAs revealed that the group mean VEP amplitude for the factor of visual-field configuration (FF versus 1/8th non-patterned octant; and FF versus 1/8th patterned octant) was significant (both at p ≤ 0.05). However, post-hoc analyses showed that each of the eight 1/8th patterned octant locations were significantly different from the mean FF response, whereas only 2 of the eight were significantly different from the mean FF response for the 1/8th non-patterned stimulus. Similar results were found for the individual subjects.
The results provided evidence that the VEP, an objective technique, could be used reliably to detect relatively small simulated scotomas in each subject. The optimal test stimulus for accurate amplitude-based assessment and spatial differentiation was the 1/8 patterned octant (Fig. 2). This isolated octant paradigm may now be extended to pilot testing in clinical patients manifesting such small and scattered scotomas (e.g., glaucoma, traumatic brain injury).
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