Optometry and Vision Sciences - Research Publications

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    Simultaneous Recording of Electroretinography and Visual Evoked Potentials in Anesthetized Rats
    Nguyen, CT ; Tsai, TI ; He, Z ; Vingrys, AJ ; Lee, PY ; Bui, BV (JOURNAL OF VISUALIZED EXPERIMENTS, 2016-07-01)
    The electroretinogram (ERG) and visual evoked potential (VEP) are commonly used to assess the integrity of the visual pathway. The ERG measures the electrical responses of the retina to light stimulation, while the VEP measures the corresponding functional integrity of the visual pathways from the retina to the primary visual cortex following the same light event. The ERG waveform can be broken down into components that reflect responses from different retinal neuronal and glial cell classes. The early components of the VEP waveform represent the integrity of the optic nerve and higher cortical centers. These recordings can be conducted in isolation or together, depending on the application. The methodology described in this paper allows simultaneous assessment of retinal and cortical visual evoked electrophysiology from both eyes and both hemispheres. This is a useful way to more comprehensively assess retinal function and the upstream effects that changes in retinal function can have on visual evoked cortical function.
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    Effect of acute intraocular pressure challenge on rat retinal and cortical function
    Tsai, Tina I. ; Bui, Bang V. ; Vingrys, Algis J. (Association for Research in Vision and Ophthalmology (ARVO), 2014)
    Purpose: The global or gross response index of visual performance measured from the eye does not necessarily translate to global responses measured from the brain. A better understanding of this relationship would facilitate the monitoring of disease models that affect the visual pathway. We consider whether rod- and cone-retino-cortical-pathways are equally affected by acute IOP elevation. Methods: Acute, stepwise IOP elevation (10, 30, 40, 50, 60, 70 mm Hg) was induced in anesthetized dark- (N = 8) and light-adapted pigmented rats (N = 6). Electroretinogram (ERG) and visual evoked potentials (VEP) were simultaneously measured after 10 minutes at each step. Relative amplitudes (treated/baseline, %) as a function of IOP level were described with a cumulative normal function. Results: Our results showed decline in scotopic and photopic ERGs with IOP elevation. Photopic ERG responses were less sensitive to IOP challenge than scotopic ERG responses. Despite significant reductions of ganglion cell–mediated waveforms at 70 mm Hg, the VEP showed only subtle decreases in amplitude. Intraocular pressure elevation produced similar effects on rod- and cone-mediated VEP waveforms. Conclusions: We show that cone signals are less sensitive than rod ERGs to acute IOP challenge. Also, retinal signals are more sensitive than are cortical signals to IOP stress, suggesting that cortical processing may act to salvage reductions expected from attenuated retinal output.