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FJ Rucker, PB Kruger; Accommodation Responses to Stimuli in Cone Contrast Space . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1492.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To identify the neural pathways for accommodation. Methods: Twelve illumination conditions were used to test specified locations in cone-contrast space for magnocellular or parvocellular contributions to a signal for reflex accommodation. A computer graphics card (VSG/2; Cambridge Research Systems) was used to create sine gratings(2c/d), that were viewed on a computer monitor (Sony GDM-F500R). Monitor resolution was 640x480 pixels with 150 Hz frame rate. Cone excitations were calculated following spectral photometry on each phosphor, as measured with Photo-Research PR-750. An achromatic doublet neutralized the longitudinal chromatic aberration of the eye, to maintain the relative cone contrasts provided by the gratings. Accommodation was monitored continuously in a Badal optometer while the grating stimulus moved (0.195 Hz) sinusoidally towards and away from the eye from a mean position of 2.00D (amplitude 1.00D). Six trials of 40.96 secs duration were run for each condition in random order. After Fourier analysis, mean gain and phase lag were calculated using vector averaging and mean accommodation response for each condition was calculated. Luminance and chromatic meridians were tested for linearity, and iso-response curves were fitted. Conditions were compared by ANOVA and t-tests. Results: Comparison by ANOVA for gain at 0.195 Hz and for mean accommodation levels showed significant differences across conditions (F=2.28; p=0.02) and (F=2.95; p=0.003) respectively. The iso-response curve for mean accommodation level showed vectors at 93.6 deg and 129 deg, with length 0.33 and 0.38, respectively. Responses at 93.6 deg (p=0.004 at 90deg) and 120 deg (p=0.003) were significantly different to the empty field response. Linearity at 120 deg was confirmed (r=0.94). The iso-response curve for gain at 0.195 Hz showed vectors at 31 deg and 120 deg, with lengths of 0.45 and 0.81, respectively. The gain response at 120 deg was not significantly different to the empty field response (p=0.125), whereas at 45 deg the response was significantly different (p=0.03). Linearity of the response at 45 deg was confirmed (r=0.99). Conclusion: At 0.195Hz mean accommodation response level is controlled by a mechanism with a strong M-cone bias. This mechanism could control the direction of the response in the presence of longitudinal chromatic aberration. Dynamic accommodation (gain) responds to the weighted sum of L-and M-cone contrasts.
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