[Fourier analysis of transient VECP in artificially increased intraocular pressure]

Usually, amplitudes and latencies are measured to analyze visual evoked cortical potentials (VECP). From the physical point of view this means an analysis in the time domain. Generally it is possible to get important information on oscillations by testing to see which frequency the power is transmitted at (frequency domain). We made such experiments on visual evoked cortical potentials with Fourier analysis during an artificial stepwise rise in the intraocular pressure. We recorded the VECP of 60 healthy young persons at a stimulus rate of 1.9 checkerboard reversals/second and analyzed the curves by Fourier transformations. We proceeded in the same way with 30 volunteers using a stimulus rate of 3.1 checkerboard reversals/second. In comparison to the VECP curves without Fourier analysis, no systemic changes in the amplitude spectra appeared during the rise in intraocular pressure. Because of this we feel that Fourier analysis mostly renders no further information and is probably dispensable for experienced clinicians when testing pressure tolerance of the optic nerve head. On the other hand, the analysis clearly showed the appearance of distortion frequencies. This may be of clinical interest in cases of severe distortion and in patients with almost extinguished VECPs. It might also be helpful to clinicians who are less experienced in electrophysiology.