Intrasession variability of the full-field ERG.

OBJECTIVES

(1) To document variability of the full-field ERG within single recording sessions under ISCEV standards. (2) To identify clinical factors contributing to the observed variability.

METHODS

Nine volunteer subjects were studied, aged 19-32 with no history of retinal disease. ISCEV standard ERGs were recorded. Dark-adapted "standard combined" and light-adapted "cone" b-wave amplitudes and implicit times were measured. Multiple flashes were presented at different interflash intervals and after different periods of dark and light adaptation. The stability of the stimulus flash was measured with a photometer.

RESULTS

The statistical coefficient of variability was roughly 2.5% for the standard combined b-wave amplitude and 4.5% for the cone b-wave. B-wave implicit times showed a coefficient of variability of 2% for standard combined responses and 1.25% for cone responses. Variation in interflash interval, dark and light adaptation times, and sporadic unusual waveforms influenced measured b-wave amplitudes.

CONCLUSION

Intrasession variability is much lower than previously reported values for intersession variability. Nonetheless, it represents a baseline of variability that will affect results and that may be minimized by recognition and control of contributing factors.