Difference of spatial summation property between b and d waves in focal electroretinogram of the cat

A new system for focal electroretinogram (ERG) using a charge-coupled device camera was developed. With this device, focal ERGs to on-off luminance modulation of uniform fields with different area (circle diameter; 16, 12, 8, 6 and 3 degrees) centered on the area centralis were recorded in 12 eyes of 6 cats. With a decrease of the stimulus area, the reduction of the amplitude in both b and d waves was observed, however, the implicit times of these waves were almost same. The amplitude ratio (12 degrees stimulus/16 degrees stimulus, 8/16, 6/16, and 3/16) of b and d waves showed statistically significant differences between the b wave and d wave (8/16, 6/16 and 3/16; p < 0.01). The difference in spatial summation property was demonstrated between the b wave and the d wave.