Navegando por Assunto "Luz - Regulação da sensibilidade"

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Estudo eletrorretinográfico da adaptação à luz de vias de processamento específicas de cone e de oponência em cor e luminância
(Universidade Federal do Pará, 2017-12-15) COSTA, Alódia Brasil; SILVA, Anderson Manoel Herculano Oliveira da; http://lattes.cnpq.br/8407177208423247
Visual system has an essential function called light adaptation or photopic adaptation, which consists in the regulation of light sensitivity allowing visual adaptation to a wide range of illumination levels. This phenomenon is not fully elucidated. Therefore, the present study aims to evaluate the magnitude and temporal pattern of the variation of retinal electrical responses for L cone and M cone selective stimuli and for luminance pathway and red-green color pathway specific stimuli, making possible the evaluation of the red-green parvocellular (P pathway) and magnocellular (M pathway) visual pathways activity, during the photopic adaptation. For such purpose, 6 healthy subjects underwent 30 minutes of dark adaptation and then were exposed a light steady background for 16 min. The stimuli were given every 2 min and the electrical retinal response was recorded by full field electroretinogram (ffERG) over 16 min. The triple silent substitution method was used to isolate the responses of pathways originating from the L or M cone. We also used specific stimuli of luminance (Lum) and red-green color (Crom). For each stimulation type was used intermediate (12 Hz, which reflects the activity of the red-green parvocellular pathway - P pathway) and high (36 Hz, which reflects the activity of the magnocellular pathway - M pathway) temporal frequency, resulting in 8 stimulation conditions. Amplitude and phase of the first (F), second (2F) and third (3F) harmonic components were extracted by Fast Fourier Transform. It was observed that amplitude and phase increased over light adaptation time with simple sine wave form in the most of components and stimulation conditions. The relative increases in F amplitude from the M-cone driven responses during the light adaptation were higher than those L-cone driven ERGs at both temporal frequencies, 12 Hz (M = 1.21, L = 0.33) and 36 Hz ( M = 1.94, L = 0.55), as well as they were higher at 36 Hz than at 12 Hz for the two cones. In general, there was slight F phase increase during the light adaptation time (<30 degrees), slightly higher at 36 Hz. Regarding the light adaptation kinetics, F amplitude and phase that seem reflect the activity of the P pathway presented a faster adaptation (L-cone 12 Hz, M-cone 12 Hz, Crom 12 Hz, Lum 12, with a mean of 1.4 min) and those that probably reflect activity of the M-pathway had slower adaptation (Lum 36 Hz, L-cone 36 Hz, M-cone 36 Hz, with a mean of 4.9 min). Thefore, M and P pathways presented different magnitude and kinetics of light adaptation, being the M pathway the pathway of greatest increase and slower adaptation.