Comparisons between behavioral and electrophysiological measures of visual function in rodent models of retinal degeneration

The critical flicker frequency (CFF) is the lowest frequency for which a flickering light appears steady. Measuring CFF indicates rod- and cone-driven function relative to light intensity. CFF can be measured by both electroretinogram (ERG) and behavior. We measured CFF in several rodent models of retinal degeneration in order to better characterize retinal degeneration and understand the functional implications of electrophysiological changes.;We measured ERG CFF in RCS dystrophic (RCS-p+) and wild type (WT) rats at PN23, PN44, and PN64. ERG CFF data in RCS rats show significant early degeneration of the rods followed by cones. CFF was significantly lower at PN23. However, rod-driven CFF was more severely reduced. At PN44 there was no longer a discernable rod-cone break. By PN64 the rod driven CFF was immeasurable in the RCS rats. We measured a- and b-wave amplitudes to bright white flashes and ERG CFF in a beta subunit GARP knockout (KO) mouse model (Cngb1-x1). At 1-month old KO mice exhibit a diminished dark-adapted b-wave and normal light-adapted b-wave compared to WT mice. Over the next 3 months, both dark- and light-adapted b-wave amplitudes declined, and the decline was greater for dark-adapted b-wave amplitudes. ERG CFF was lower for the KO mice at scotopic intensities, but normal at photopic intensities at one month of age. CFF values remained stable in the KO mice as the b-wave amplitudes decreased with age. We measured a- and b-wave amplitudes to bright white flashes and CFF before and after a 10-day period of low-intensity (280 lux) light-damage in albino rats. Dark- and light adapted ERG responses were significantly reduced after light damage. The a-wave was permanently reduced, while b-wave amplitude recovered over 80% by R20. There was a small, but significant dip in scotopic ERG CFF at R6. Photopic behavioral CFF was slightly lower following light damage.;Retinal degeneration did not consistently reduce CFF. In general, ERG thresholds were better preserved than ERG maximum amplitudes. We found that CFF measured by ERG agreed with behavioral measures. The preservation of threshold responses that mediate behavior has positive implications for the clinic.