Averaged steady-state visual evoked cortical potentials at artificially raised intraocular pressure.

By recording steady-state visual evoked cortical potentials while intraocular pressure is artificially increased, information can be obtained on the pressure tolerance of the optic nerve head. Such experiments have previously been performed by a vector voltmeter technique. We studied the visual evoked cortical potentials in 30 healthy volunteers with artificially increased intraocular pressure, but we used an averager instead of a vector voltmeter. The results were similar except that the noise level in averaging was higher than with the vector voltmeter technique. This observation confirms that the signal-to-noise ratio is much better with the vector voltmeter technique than with the averaging technique. Our results show that averaging can be used in pressure tolerance testing, but the amplitude cannot be observed as far down as in the vector voltmeter technique. This limits the clinical value of averagers in this application.