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C. B. Y. Kim, J. N. Ver Hoeve, T. M. Nork; Multifocal Visual Evoked Potentials in Cynomolgus Monkeys With Unilateral Chronic Intraocular Pressure Elevation. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2338.
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© ARVO (1962-2015); The Authors (2016-present)
Recently, we demonstrated the feasibility of using a large, 7-element hexagonal array to measure multifocal visual evoked potentials (mfVEPs) from delimited portions of the visual field in nonhuman primates anesthetized with intravenously administered barbiturate (Curr Eye Res 31:885-893, 2006). The purpose of this study is to use the mfVEP technique to investigate cortical response changes in cynomolgus monkeys following induction of chronic elevated intraocular pressure (IOP).
3 cynomolgus monkeys (2 females and 1 male) were studied. After 6-7 baseline mfVEPs were recorded, the IOP in one eye was elevated by photocoagulation of the trabecular meshwork. IOP (measured weekly with a Tonopen-XL) was elevated for a duration of 1.1-1.4 yr. During this period, 15-17 mfVEPs were recorded. mf-electroretinograms (mfERGs) were recorded simultaneously with mfVEPs using the VERIS Science 4.9 system. Animals were anesthetized with pentobarbital sodium (10-15 mg/kg IV). Two VEP channels were recorded from occipital scalp sites. Eyes were refracted for the 20-cm testing distance. The stimulus was a 7-element hexagonal array subtending ~ 80 deg with mean luminance of 100 cd/m2. A binary m-sequence of 215-1 with base period of 13.3 ms was used. First-order kernel (K1) and second-order kernel, first slice (K2.1) signal-to-noise ratios (SNR) of the root mean square (RMS) from each element were analyzed using separate repeated measures ANOVAs with hexagon location, tested eye, and IOP period as factors.
In all animals, the central hexagon (21 deg) produced the most robust and reproducible mfVEP responses whereas the mfVEP was largely diminished in the 6 surrounding peripheral (>21 to 80 deg) hexagons. In contrast, the simultaneously recorded mfERG responses were substantial at all 7 hexagonal locations in both eyes. ANOVA revealed significant mfVEP decrements occurred during IOP elevation for both K1 and K2.1 responses compared to baseline and with the fellow eye. Mean K2.1, but not K1, mfVEP from the central element decreased 2.3-fold in RMS SNR across the study.
The large-element hexagonal stimulus array elicits reliable cortical potentials with large SNR from delimited portions of the visual field. These ‘luminance’ mfVEPs are sensitive to the effects of chronic IOP elevation. K2.1 of the cortical mfVEP was most sensitive to the effects of elevated IOP. mfVEPs evoked by large luminance fields may be a useful measure of progression in experimental glaucoma, particularly when spatial resolution is less important than high SNR recordings.
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