Data from: Individual objective and subjective fixation disparity in near vision

Binocular vision refers to the integration of images in the two eyes for improved visual performance and depth perception. One aspect of binocular vision is the fixation disparity, which is a suboptimal condition in individuals with respect to binocular eye movement control and subsequent neural processing. The objective fixation disparity refers to the vergence angle between the visual axes, which is measured with eye trackers. Subjective fixation disparity is tested with two monocular nonius lines which indicate the physical nonius separation required for perceived alignment. Subjective and objective fixation disparity represent the different physiological mechanisms of motor and sensory fusion, but the precise relation between these two is still unclear. This study measures both types of fixation disparity at viewing distances of 40, 30, and 24 cm while observers fixated a central stationary fusion target. 20 young adult subjects with normal binocular vision were tested repeatedly to investigate individual differences. For heterophoria and subjective fixation disparity, this study replicated that the binocular system does not properly adjust to near targets: outward (exo) deviations typically increase as the viewing distance is shortened. This exo proximity effect—however—was not found for objective fixation disparity, which–on the average–was zero. But individuals can have reliable outward (exo) or inward (eso) vergence errors. Cases with eso objective fixation disparity tend to have less exo states of subjective fixation disparity and heterophoria. In summary, the two types of fixation disparity seem to respond in a different way when the viewing distance is shortened. Motor and sensory fusion–as reflected by objective and subjective fixation disparity–exhibit complex interactions that may differ between individuals (eso versus exo) and vary with viewing distance (far versus near vision).LMER_dataThis file contains the data for linear mixed effects models (LMER in R) with the variables: subject, viewing distances 40, 30, 24 cm, session 1 and 2, repetition 1, 2, 3 and 4 per session, heterophoria, objective fixation disparity, subjective fixation disparity, relative vergence stimulus.Coefficients of robust regressionThis file contains the coefficients of the robust regression (lmrob in R) which provides the intercept (dependent variable at 30 cm viewing distance) and the slope (change in the dependent variable with viewing distance) as shown in Fig. 4. These coefficients are based on the data of each session. The three dependent variables were objective fixation disparity, subjective fixation disparity and heterophoria. Additional variables for Fig. 8 refer to the accommodative performance: the AC/A ratio and the accommodative response at 30 cm viewing distance.RobCoeff_oFD_sFD_het_acc.tx