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Philip R. Nolan, J.Jason McAnany; The Effects Of Light Adaptation On The Harmonic Components Of The Flicker Electroretinogram. Invest. Ophthalmol. Vis. Sci. 2012;53(14):5704.
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© ARVO (1962-2015); The Authors (2016-present)
This study evaluated the effects of light adaptation on the harmonic components of the 31-Hz flicker ERG to determine how changes in these response components affect the shape of the flicker ERG during light adaptation.
Full-field ERGs were recorded from three subjects with no history of eye disease (ages 24 to 60 years) using a Diagnosys stimulating and recording system and conventional recording techniques. Following 30 minutes ofdark-adaptation, the subjects were exposed to a uniform adapting field of 50cd/m2 that was generated by the sum of middle- and long-wavelength LEDs. The field, which was presented for approximately 15 minutes, was intermittentlymodulated sinusoidally for approximately 1 s at a temporal frequency of 31.25 Hz.The ERG was recorded during the sinusoidal modulation and Fourier analysis was used to obtain the response amplitude and phase of the fundamental, second, and third harmonic components.
The fundamental response amplitude increased by almost a factor of two, over approximately 9 minutes, consistent with previous reports. The amplitude of the second harmonic also increased by almost a factor of two, although the time-course was approximately ten times faster than that of the fundamental. The amplitude of third harmonic component increased by a factor of four, a larger increase than that of the fundamental or second harmonic, with a time-course that was between that of the fundamental and second harmonic. The phase of the fundamental was unaffected by light adaptation, whereas the phase of the second and third harmonic components both increased by 45 degrees. However, the phase of the second harmonic component had a time-course that was slower than the third harmonic component.
Light adaptation had different effects on the first, second, and third harmonic components of the 31-Hz flicker ERG, which resulted in the response becoming progressively less sinusoidal over the course of adaptation. The differential effect of light adaption on the harmonic components is consistent with multiple retinal sites of light adaptation.
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