CHECK SIZE TUNING OF THE PATTERN ELECTRORETINGORAM - A REAPPRAISAL

The pattern electroretinogram was recorded to checkerboard stimuli wit h a wide range of check sizes and two stimulus field sizes. Check size s ranged from 0.25 degrees to 7 degrees (field size, 16 degrees x 14 d egrees) and 0.25 degrees to 15 degrees (field size, 32 degrees x 27 de grees) in 14 and seven subjects, respectively Reversal rate was 4.5/s. For minimal intrusion of blink artifacts the interrupted stimulation technique was employed. The P50 and N95 components of the pattern elec troretinogram were evaluated separately. With both stimulus held sizes amplitude of P50 and N95 was maximal between 0.75 degrees and 1 degre es. With smaller check sizes the amplitude dropped monotonically. With larger check sizes field size played a role: with the 16 degrees x 14 degrees field, P50 gradually dropped to 89% from 1 degrees to 7 degre es, which was paralleled by N95 only up to 7 degrees, where N95 droppe d to 81% (p<0.05). With the 32 degrees x 27 degrees field, there was n o significant difference in size dependency between P50 and N95 for la rge checks, both components staying constant from 1 degrees to 15 degr ees. We conclude that there is only minor large-check attenuation of t he pattern electroretinogram, especially with a large field. The appar ent field-size dependency may explain previous discrepancies in the li terature.