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Indu Vedamurthy, Dorothy Nguyen, Clifton Schor; Cross-coupling between convergence and accommodation is optimized for a broad range of directions and distances of gaze. Journal of Vision 2007;7(15):111. doi: 10.1167/7.15.111.
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Accommodation and convergence systems are cross-coupled. Historically, the gains of the cross coupling (AC/A and CA/C ratios) have been quantified for targets in the mid-sagittal plane where stimuli to accommodation and vergence are equal when expressed in diopters and meter-angles. However targets at non-zero azimuth angles present unequal stimuli for accommodation and vergence. Are the cross-links between the two systems calibrated to compensate for mismatches that increase with azimuth? We measured the response AC/A and CA/C ratios at zero azimuth, 17.5 and 30 degrees rightward gaze eccentricities with a Badal Optometer and Wheatstone-mirror haploscope. AC/A ratios were measured under open-loop vergence conditions along the iso-accommodation circle (locus of points that stimulate approximately equal amounts of accommodation to the two eyes at all azimuth angles). CA/C ratios were measured under open-loop accommodation conditions along the iso-vergence circle (locus of points that stimulate constant convergence at all azimuth angles). Our results show that the gain of accommodative vergence (AC/A) decreased and the bias of convergence accommodation (tonic accommodation) increased at the 30 deg gaze eccentricity. These changes are in directions that compensate for stimulus mismatches caused by spatial-viewing geometry during asymmetric convergence.
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