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C.E. Riva, E. Logean, B. Falsini; Optic Disc Reflectance Changes Induced by Flicker Stimulation. Relationship With Retinal Activity . Invest. Ophthalmol. Vis. Sci. 2005;46(13):3917.
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Purpose: To investigate the optic disc reflectance change (dR) in response to diffuse flicker stimulation and determine the relationship between dR and retinal neural activity and blood flow. Methods: Reflectance (R) at 810 nm (isobestic wavelength) was measured from a 150–microns diameter area of the optic disc tissue during various types of diffuse flicker stimuli: a) 15–Hz red–green flicker at various color ratios cr = red/(red + green); b) red–green flicker with cr = 0.8 at various frequencies; c) pure 15–Hz luminance flicker at various luminances. Simultaneously with R, we also determined the volume (Vol) and flow (F) of blood at the papilla by laser Doppler flowmetry (LDF) and the ERG 1st (1F) and 2nd (2F) harmonic components. Correlations were established between the changes of Vol (dVol), F (dF) and dR and the 1F and 2F components. Results: In response to the variation of cr of the 15–Hz chromatic flicker (4 subjects), R and ERG 1F, as well as R and ERG 2F were significantly correlated (r = 0.32, and r = 0.44, both p < 0.01). Significant correlations were also observed between dR and dF and dR and dVol (r = 0.42, p < 0.01). Varying the frequency of the chromatic flicker with cr = 0.8 (M–cone isolation, one subject) resulted in a significant correlation between dR and ERG 1F (r = 0.86, p < 0.01) and between dR and dVol (r = 0.67, p = 0.05). Varying the luminance of the 15–Hz pure luminance flicker (5 subjects) showed no correlation between dR and each of the ERG 1F and 2F, but the correlation between dF and ERG 2F was significant (r = 0.35, p < 0.01). Conclusions: We have previously demonstrated a coupling between blood flow at the disc and retinal activity. The present work now suggests a coupling between optic disc reflectance and retinal activity, the strength of which depends upon the type of retinal stimulation. Although this coupling may be partially due to blood flow– or volume–induced dR during stimulation, some other factors, such as changes in optic disc tissue scattering may contribute to dR.
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