[Simultaneous registration of VECP and pattern ERG during artificially raised intraocular pressure]

The visual evoked cortical potentials (VECP) are changed by the artificial increase in intraocular pressure (IOP). The exact location of the damage is still unclear. One possibility is that the increased ocular pressure reduces the blood flow in the optic nerve head. The function of the optic nerve fiber function would be decreased by this effect. Another possibility is that the generation of the signals in the retinal ganglion cells could be influenced by the artificial pressure enhancement. We developed a method of simultaneous recording pattern reversal electroretinograms (PERG) and VECP during artificially raised IOP. The PERG was recorded by cutaneous electrodes (Grass, USA; diameter 5 mm), which were positioned close to the lid margins. The pattern reversal rate was 7.9 reversals/s. In a pilot study, we examined 10 healthy volunteers with artificially increased ocular pressure. In 9 cases, amplitudes showed a more stable behavior in the VECP than in the PERG: the mathematical behavior of the amplitude/pressure curves was more stable in the VECP of 6 volunteers and once in the PERG. Signs of very sufficient autoregulation could be found in the VECP of 7 volunteers and once in the PERG. The critical pressure, at which a further increase in IOP causes a continuous amplitude decrease to the noise level, was 9 times more stable in VECP (median 53 mmHg) than in PERG (median 48 mmHg). The results lead to the conclusion that in healthy persons the artificial pressure rise influences the ganglion cells at an earlier timepoint than the signal transmission in the axons.