Fast ERG 15 Hz flicker protocol for assessing functional changes in the rod system

To establish a clinically applicable dark-adapted 15 Hz flicker electroretinogram (ERG) for sensitive detection of functional changes in the fast and the slow retinal rod pathways.

The study consisted of two parts. In the first part, the paradigm of the previously demonstrated "null-effect" of stimulus luminance on ERG-amplitudes for 15 Hz flicker stimuli with duration of 2.5 s was reexamined. In the second part an optimized faster protocol designed for routine clinical use was tested and compared with the results from the first part and data published in the past. The 15-Hz flicker ERG protocol included 12 steps with different intensities ranging from 0.00019 scot cd.s/m² to 0.05 scot cd.s/m² and was obtained from 15 normally sighted subjects. Stimulus flashes were presented in blue (448 nm) and white, alternating in each luminance step after 20 min of dark adaptation. A shorter version containing only 7 steps was selected with intensities ranging from 0.00031 scot cd.s/m² to 0.005 scot cd.s/m². Additionally, the stimulus paradigm included noise measurement to properly estimate the signal-to-noise ratio.

The results from the first protocol showed a U-shaped amplitude vs. luminance response curve at 15 Hz, consistent with previously published results. Using the new, shortened protocol, we also obtained similar results, but with a much shorter recording time. Based on the signal-to-noise ratio from these measurements a reliable measurement can be obtained in only 2.5 min which presents a considerable time reduction necessary to record a 15 Hz response curve in a clinical setup.

The new protocol is suitable for integration into a daily clinical environment, offering short and well-balanced protocols to address complex retinal network interactions.