EFFECTS OF LIGHT SCATTER, DEFOCUSING, MEAN LUMINOSITY, CONTRAST, AND CENTRAL SCOTOMA ON THE PVER AMPLITUDE-CHECK SIZE FUNCTION CURVE

We analyzed the effects of various stimulus parameters, ie, light scat ter, defocusing, mean luminosity, contrast, and central scotoma, on th e normal pattern reversal visual evoked response (PVER), amplitude-che ck size function curve in six normal subjects. The steady-state PVER w as recorded with five check sizes ranging from 160 to 10 min 1-octave increments. The PVER amplitude, especially with the smaller check size s, was markedly decreased by light scatter induced by acrylic sheets. The function curve quickly changed to a low pass filter shape when +2. 0 diopters of defocus were added, with the decrease most marked in the small check sizes. When the mean luminosity was decreased, the functi on curve maintained its normal inverted-U shape up to 5 cd/m2, but the shape flattened with lower luminosity. Amplitude decreases were seen with all check sizes in low luminosity. With contrast changes from 95 to 24%, the function curve maintained its normal shape, but with sligh tly reduced amplitudes. The amplitude decrease was moderate even with the lowest contrast. With a two-degree central scotoma, the PVER ampli tude was reduced more with the smaller than the larger check sizes. Th e function curve became somewhat flatter, with its peak shifting to th e larger check sizes. Results indicated that the shape of the PVER amp litude-check size function curve changes in response to different mode s of stimulation.