SBNeC 2010
Resumo:C.032


Prêmio
C.032First and second harmonic responses of heterochromatic flicker ERGs reflecting luminance and cone opponent mechanisms in normal trichromats and one deuteranopic observer
Autores:Mirella Telles Salgueiro Barboni (USP - Neuroscience and Behavior, University of Sao Paulo) ; Dora Fix Ventura (USP - Neuroscience and Behavior, University of Sao Paulo) ; Jan Kremers (FAU - Department of Ophthalmology,University of Erlangen-Nuremberg)

Resumo

Purpose: To analyze 1st and 2nd harmonic responses of heterochromatic flicker ERGs reflecting luminance (higher temporal frequency = 36 Hz) and cone opponent (lower temporal frequency = 12 Hz) mechanisms. Methods: Flicker ERGs were recorded with a DTL fiber electrode from the right dilated eye of 12 normal trichromats (mean age = 35 ± 8 years old; 8 males and 4 females) and one eye of a 30 years old deuteranopic observer. Red and green LEDs were modulated in counterphase on a Ganzfeld stimulator with a mean luminance of each LED of 100 cd/m² and a yellow mean chromaticity (CIE: x = 0.2016 and y = 0.7371). 15 different stimulus conditions varying the fraction of red modulation (red/[red+green]) between 0 and 1 were employed. The measurements were repeated at 36 Hz and 12 Hz. The recordings were Fourier analyzed and the responses were defined as amplitudes (in microvolts) and phases (in degrees) of the 1st and the 2nd harmonic components. Results: 1st harmonic: the response amplitudes at 36 Hz measured in normal trichromats depended on stimulus condition and displayed a “V” shape curve. At that the stimulus condition resulting in a minimal response, the phase shifted by 180º. At 12 Hz, the response amplitudes and phases were relatively constant. The 36 Hz response amplitudes of the deuteranopic observer also displayed a “V” shape dependency on stimulus condition. However, the condition for a minimal response and a concomitant phase shift was displaced to the left and coincided with the silent substitution condition of the L-cones. At 12 Hz the response amplitudes were smaller for the deuteranopic observer compared to the trichromats. In addition there still was a condition in which the response was minimal and where the phase shifted by 180º, this was the L-cone silent substitution condition. 2nd harmonic: at 36 Hz the response amplitudes were much lower compared to the 1st harmonic and the deuteranopic observer showed similar responses. At 12 Hz the 2nd harmonic component depended on stimulus condition in a similar manner as the 36 Hz 1st harmonic component and the deuteranopic observer showed lower response amplitudes. Conclusions: As it was previously reported (Kremers et al., 2010, IOVS 51: 577-587), it is possible to measure luminance (M pathway) and cone opponent (P pathway) post-receptoral retinal mechanisms based upon noninvasive electrophysiological responses in normal trichromats. At 36 Hz, the 2nd harmonic component depended on stimulus condition in a similar manner as the 1st harmonic indicating that the 2nd harmonic reflects a deviation from a sinusoidal response but not an activity in a distinct pathway. In contrast, at 12 Hz the 1st and the 2nd harmonic components in normal trichromats depended differently on red fraction, indicating activity in distinct pathways. Possibly, activity of the luminance channel (M pathway) may significantly influence the 2nd harmonic component of heterochromatic modulated flicker ERGs at 12 Hz. The 12 and 36 Hz 1st and 2nd harmonic components in the deuteranopic observer all depended similarly on stimulus condition, indicating that all responses are determined by a single response pathway.


Palavras-chave:  retina, electroretinogram, color contrast, luminance contrast, human vision