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Spatial Resolution in the Common Marmoset Measured With Visual Evoked Potentials

The New England College of Optometry, Boston, MA

Commercial Relationships: W.R. Steigerwald, None; J.A. Potter, None; G. McCormack, None; D. Troilo, None.

Support: NIH Grant EY11228

Abstract

Purpose: The common marmoset is a New World primate used in experimental studies of the development of refractive state. Little is known about the spatial resolution capabilities of the marmoset visual system; foveal cone density measurements estimate nyquist limits to be approximately 30 cycles–per–degree (cpd) (Troilo et al. 1993, Vision Research, 33:1301), and single unit recordings in primary visual cortex report a cut–off spatial resolution of 9 cpd (Sengpiel et al. 1996, Visual Neuroscience, 13:145). The purpose of this study was to develop a non–invasive procedure for measuring spatial resolution of the marmoset for use in our studies of the visual control of eye growth and refraction.

Methods: Four conscious untreated marmosets were tested binocularly and monocularly using a modified sweep visual evoked potential (VEP) paradigm based on the Freiburg EP2000 system (courtesy of Michael Bach). A checkerboard stimulus (40% contrast) alternating at a rate of 7.5 Hz was presented at six different check–sizes (corresponding to dominant spatial frequencies of 1.0 to 8.2 cpd). Each checkerboard stimulus was presented for 10 seconds. in sequence from low to high spatial frequency. The sequence was repeated 6 times and the signals averaged. VEP signals were band–pass filtered, amplified, and analyzed off–line. The amplitudes of the VEP signals were plotted against spatial frequency and a linear regression extrapolated to predict the highest resolvable spatial frequency.

Results: Repeated measures of spatial resolution showed that the technique has a 95% CI of 2.7 cpd. The average spatial resolution measured binocularly and monocularly for all animals was 11 (±2.9 SD) and 7.5 cpd (±1.9 SD), respectively. Interocular differences in monocularly determined resolutions were on average less than 1 cpd.

Conclusions: Our estimates of spatial resolution in the marmoset measured by VEP are within predictions based on anatomy and signal unit recordings. This VEP technique for determining spatial resolution has potential use in marmosets undergoing experimental manipulations of visual experience that affect eye growth, refraction, and possibly visual acuity.

Keywords: electrophysiology: non-clinical • visual acuity • refractive error development

© 2005, The Association for Research in Vision and Ophthalmology, Inc., all rights reserved. For permission to reproduce any part of this abstract, contact the ARVO Office at arvo{at}arvo.org.