Purchase this article with an account.
M. R. Shah, H. Qian; Comparison of Rat Cone ERG Elicited by Pulsed Flicker and Sine-Wave Modulated Light Stimuli. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2170.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Pulsed light stimulus is commonly used to elicit flicker ERG, whereas sine-wave modulated light provides better characterization of frequency-response relation. Here, we compared rat cone flicker ERG elicited by these two stimuli in frequency domain, and investigated the mechanism for the higher harmonic responses.
Adult rats (both albino and pigmented) were anesthetized with ketamine and xylazine. Light stimuli were delivered by pulse-width modulated LEDs. A background light (5 cd/m2) was used to saturate the rod pathway. Pulse flickers were composed of 4 ms flashes (peak luminance of 690 cd/m2) delivered at various temporal frequencies (2 to 12 Hz). To study the effects of light intensity on flicker ERG, the peak luminance of pulses were varied from 25 to 690 cd/m2. The sine-wave modulated light had a mean luminance of 100 cd/m2 and contrast of 90%. The amplitudes and phases of the harmonic responses were derived from discrete Fourier transforms using Matlab.
The frequency-response relations for pulse flicker ERG (FP) were derived from harmonic components in frequency domain and compared with the fundamental response to sine-wave flickers (FS). For response frequencies < 30 Hz, FP exhibited similar shape as FS, although the amplitude of the response varied with stimulus frequency. For response frequencies > 30 Hz, FP consistently exhibit larger peaks than FS. These high harmonic components in FP were present for all flash frequencies tested (2-12 Hz). When flashed at 6Hz, the high harmonic components persisted with the flash luminance varied from 25 cd/m2 to 690 cd/m2. Two potential mechanisms for the high harmonic components were considered: nonlinear response to harmonic components in pulsed flash and oscillatory potentials. Intravitreal injection of bicuculline blocked oscillatory potentials, and reduced the amplitude of high harmonic components. On the other hand, the nonlinear responses of flicker ERG, measured as a beat response to light modulated through a mixture of two sine waves, were enhanced in bicuculline injected eyes.
Pulse light stimuli can be used as an alternative method to probe the frequency-response relationship of flicker ERG for <30 Hz responses. Pulsed flicker ERG also contains high harmonic components which are composed of oscillatory potentials and nonlinear responses in flicker ERG.
This PDF is available to Subscribers Only