[Total average values of transient visual evoked cortical potentials in tests of the pressure tolerance of the optic nerve]

Transient visually evoked cortical potentials were recorded during an artificial stepwise rise of intraocular pressure. At each pressure step one average was taken. The reversal rate was 1.9 Hz. Two groups of 30 healthy volunteers each were examined: in group one 25 sweeps were averaged and in group two 50 sweeps. Thus the recording time in group two was doubled compared to group one. When all subjects were examined the evoked potentials of the 30 subjects were averaged at each pressure step: the results was a "Grand Average" at the different pressure steps applied. The amplitudes of N2-P2 were plotted versus the intraocular pressure. It is seen that a not monotone or weakly monotone function in the amplitude/pressure curve is more clearly seen in the averages of 25 sweeps. We interpret this result as follows: a not monotone or weakly monotone behaviour is a sign of autoregulation in the optic nerve head. This sign is more clearly shown at a short recording time. The majority of healthy persons show autoregulation, the majority of glaucoma patients do not. According to the results presented here it is advisable to apply short recording times in clinical pressure tolerance testing of the optic nerve head. A short recording time enhances the accuracy of the test.