Adaptation Dynamics Measures in Simultaneously Recorded Pattern Electroretinograms and Visual Evoked Responses

In this study a new methodology to measure adaptation dynamics of simultaneously recorded Pattern ElectroRetinoGrams (PERG) and Visual Evoked Potentials (PVEP) were developed. Monocular PERGs and VEPs were recorded in response to randomly delivered bursts (1 through 8) of visual reversal displays in ten adult normal subjects. Reversals were 102ms apart and reversal bursts were separated with 510ms intervals. Stimuli were horizontal gratings presented on a custom made display designed using fast onset/offset white LEDs. Responses to individual reversals were obtained by simultaneous two channel continuous recordings. Data were processed offline by selective averaging based on burst size followed by subtraction and shifting of the previous consecutive burst responses from the last consecutive burst response. The results showed that PERG (N35-P50) component showed little change (no adaptation) while (P50-N95) reduced 20% in the second reversal (adaptation <;200ms). VEP (N75P100) and (P100-N135) components, on the other hand, exhibited dramatic reduction (35%) in the first four reversals (adaptation<;500ms) before it stabilized. The methodology presented provides rapidly acquired and repeatable quantitative measures of visual adaptation dynamics for different structures of the visual pathway and may be useful in early detection of various neuroophthalmic diseases.