mfVEP and mfERG in Monkeys with and without Continuous Stimulus Position Monitoring

Abstract

Abstract: : Purpose:To compare multifocal visual evoked potentials (mfVEP) and multifocal electroretinograms (mfERGs) obtained with and without continuous stimulus positioning monitoring (cspm), and to compare mfERG responses recorded with laser versus a cathode ray tube monitor (CRT) for stimulation. Methods:Unscaled stimulus arrays, containing a variable number of hexagons, were used to elicit mfERGs in Cynomolgus monkeys. mfVEPs were evoked with a quadratic 4X4 checkerboard, each element divided into smaller checks alternating between black and white. During both mfVEP and mfERG recordings the fundus structures were monitored through the infrared channel of a scanning-laser ophthalmoscope (SLO), thus permitting cspm. The stimulus was then added either by a miniature CRT projecting into the optical pathway of the SLO, or the 514 nm Argon channel of the SLO (mfERG only). Alternatively, recordings were conducted with the stimuli projected on a CRT screen at a distance of 33 cm. All recordings were performed with a VERIS system except the argon channel stimulation performed with a Roland Consult system. Results:mfVEPs obtained with and without cspm yielded similar results, with large central responses and very small peripheral ones. A high resolution of 12X12 alternating checks in each element was found best for the CRT screen stimulation, whereas a lower resolution of 2X2 was most suitable when using cspm. mfERGs were well recordable with all three modes of stimulation. However, once the size of the hexagons became small, the trace array amplitudes showed a central dip rather than the usual peak. Conclusions:We have shown, for the first time, the feasibility of recording mfVEP in monkeys, which may provide a tool for the study of retino-cortical pathway disorders such as glaucoma and optic neuritis. Cspm facilitates positioning and refractive correction in mfVEP and mfERG recordings in non-verbal subjects. The larger optimal pattern size in mfVEP with cspm (which features a smaller projection area compared to standard CRT screen stimulation), together with the loss of the central peak in mfERG with increasing number of hexagons, indicates that there may be a minimal area size required for both methods. This will be further investigated.

Keywords: electrophysiology: non-clinical • animal model • imaging methods (CT, FA, ICG, MRI, OCT, RTA, S