Optimizing ERG Measures of Scotopic and Photopic Critical Flicker Frequency

A visual response to flickering light requires complex retinal computation, and thus ERG measures are an excellent test of retinal circuit fidelity. Critical flicker frequency (CFF) is the frequency at which the retinal response is no longer modulated. Traditionally, CFF is obtained with a series of steady flicker stimuli with increasing frequencies. However, this method is slow and susceptible to experimental drift and/or adaptational effects. The current study compares the steady flicker method to CFF measurements obtained using a frequency sweep protocol. We introduce a light source programmed to produce a linear sweep of frequencies in a single trial. Using the traditional steady flicker method and a criterion response of 3 μV, we obtained a scotopic CFF of 18.4 ± 0.66 Hz and a photopic CFF of 44.4 ± 1.67 Hz. Our sweep flicker method, used on the same animals, produces a waveform best analyzed by Fourier transform; wherein a 6.18 log μV² threshold was found to yield CFF values equal to those of the steady flicker method. Thus, the two flicker ERG techniques give comparable results, under both dark- and light-adapted conditions, and the flicker sweep method is faster to administer and analyze and may be less susceptible to blinking, breathing, and eye movement artifacts.