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K. E. Bowles, T. W. Kraft; ERG Assessment of CFF in Older and Younger Human Subjects. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3808.
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© ARVO (1962-2015); The Authors (2016-present)
Critical flicker frequency (CFF) measures the highest frequency that is perceived as flickering for a given mean illumination. In order to assess the variability in electrophysiological CFF with age, we have administered a mesopic and photopic flicker ERG test to a healthy population of older and younger adults.
Flickering stimuli were presented to subjects in two age groups: young (20-30 year-old) and old subjects (50-70 years old). All subjects were treated according to the Declaration of Helsinki. Four mean illumination levels were used: 0.3, 2.0, 20 and 200 cd/m2. The stimulus produced 100% Michelson contrast. Flicker frequency varied from 5 to 64 Hz. In addition, subjects were given the ISCEV standard dark-adapted ERG, light adapted ERG and 30 Hz Flicker tests. Flicker ERGs were analyzed by measuring fast Fourier transform (FFT) and taking the power at the driving frequency as the response to the stimulus. CFF was determined by fitting a line to the log-FFT-response peak vs. frequency plot and measuring threshold at the noise level of the recordings.
All subjects tested produced normal results by the ISCEV standard ERG. At our highest stimulus intensities (20 cd/m2 and 200 cd/m2) the older and younger groups had intermixed CFF results. At 0.3 cd/m2 the younger subjects had higher CFF than the older subjects. At 2.0 cd/m2 the younger subjects generally had higher CFF than older subjects, but there was some overlap.
Our electrophysiological results suggest that younger subjects have a higher CFF than older subjects at lower light intensities. These results are consistent with published psychophysical measurements of CFF and correlate well with the documented are-related loss of rod photoreceptors. By establishing as set of normative values based on ERG flicker, subjects with rod and cone dysfunctions, such as age related macular degeneration, might be identified and followed on a quantitative basis.
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