Visual evoked potential correlates of laser flashblindness in rhesus monkeys. II. Doubled-neodymium laser flashes.

The effects of Q-switched (20-ns) doubled-neodymium (Nd-2) laser flashes upon the visual evoked potential (VEP) of two rhesus monkeys were studied and compared with the effects of 100-ms argon laser flashes described previously. VEP's were recorded under barbiturate anesthesia using bipolar electrodes chronically implanted in foveal striate cortex, and were elicited by 6-Hz phase-reversing gratings. The parameters which were investigated included the retinal area and energy level of the flash, and the wavelength, spatial frequency, and contrast of the test grating. The effects produced by the Q-switched pulses at 50% of the maximum permissible exposure (MPE) were smaller in magnitude than those produced by the longer duration argon flashes. The reduced effects of the Nd-2 pulses were attributed to the lower energy contained in these flashes, as dictated by the MPE standards. In other respects, the Nd-2 flash effects closely paralleled the argon effects. The results of the various experiments suggest that VEP decrements produced by long and short flashes are similar at equal energy levels, despite the fact that the shorter flashes are believed to produce considerably less pigment bleaching.