EFFECT OF PHARMACOLOGICALLY INDUCED MYDRIASIS ON NORMAL VARIABILITY OF RETINAL OSCILLATORY POTENTIALS IN MAN

In this study we describe certain aspects of normal variability of osc illatory potentials, with particular reference to interaction between pupil size and stimulus intensity. The mean latencies of the earlier o scillatory potentials, O1 and O2, were significantly shorter when adop ting the dilated pupil condition than when stimulating with a normal p upil. This occurred at various light intensities, although the differe nce was more significant at the highest intensity. O1 and O2 latencies became significantly longer as the stimulus intensity was progressive ly reduced. The latencies of the later components O3 and O4 were unaff ected. The O1 and O2 amplitudes were not influenced by pupil size, but a significant reduction occurred with the progressive decrease in sti mulus intensity. The later components O3 and O4 are greatly reduced in amplitude after pupil dilatation using higher stimulus intensities; t he O4 potential may even disappear in 10% of the cases. These data pro vide further support for the existence of two distinct behavior patter ns for earlier and later oscillatory potentials. Although light adapta tion may affect oscillatory potentials, we suggest that in our experim ental conditions, oscillatory potential changes may occur as a result of the activity of the neural modulating system, not only as a result of photoreceptor interaction.