The human suprathreshold photopic oscillatory potentials: method of analysis and clinical application

The oscillatory potentials (OPs) of the electroretinogram (ERG) identify the high frequency wavelets which are seen riding on the top of the ascending limb of the b-wave. Despite the refinement in ERG recording techniques, which now allow for a more selective amplification of the OPs, their clinical utility still remains somewhat limited. Furthermore, while it has long been recognized that the different OPs which builds a given response are generated by distinct retinal events, amplitudes of clinically recorded oscillatory potentials are still reported using the artificial variable 'sum of OPs (SOPs)' which represent the sum amplitude of all the OPs identified in a given response; a method which is prone to compromise the diagnostic possibilities of the oscillatory potential response. The purpose of this report is to present a method of analysis of the OP response which is based on the relative amplitude of each OP. For the sake of clarity this report will focus on the analysis of the suprathreshold photopic OP response evoked the flash for 8.9 cd-m-2-sec in energy delivered against a rod desensitizing background of 30 cd-m-2 in luminance. The amplitude of each of the three major OPs (ie: OP2, OP3 and OP4) that normally compose this response was reported in relative units (ie: OP chi/SOPs) a method shown to minimize intersubject variability and at the same time allow for each OP to be evaluated individually. With the above method I have reviewed 289 clinical OP responses collected during a 7 year interval and identified more than 10 different categories of responses of which 6 were shown to demonstrate specific anomalies for one or two OPs. The selectivity and reproducibility of my observation were confirmed on follow-up testings as well as in pedigree studies. Use of this method of OP analysis should significantly increase the clinical utility of the oscillatory potentials and also facilitate comparisons between clinical laboratories.