Table 1.
Subject characteristics.
Figure 1.
Schematic diagrams of stimulus configurations and task procedure.
(a) Illustration of dichoptic stimulus presentation; (b) Illustration of two stimulus configurations. In the positive configuration, the phase of the grating in the weak eye was shifted by θ/2 ( = 45°) from the midline while the phase in the strong eye was shifted by -θ/2. In the negative configuration, the phase-shift was reversed; (c) An example of the perceived phase (θ′) versus interocular contrast ratio δ. The perceived phase was measured as a function of interocular contrast ratio. The resulting data were fitted with the attenuation model [7] to compute effective contrast ratio. The black solid line is the best fit of the model. The dotted arrow line (magenta) indicates the estimated effective contrast ratio for this normally-sighted subject.
Figure 2.
Examples of individual subject data.
Each panel contains the perceived phase versus interocular contrast ratio function (red circles) of a representative subject from each group. Subject's age, angular eye deviation (type and amount of deviation), fixational information (fuses, left or right eye) and visual acuity are also shown in each panel. The data were fitted with the attenuation model (Eq. 4) to estimate effective contrast ratio (ECR) of the weak eye. The black solid lines are the best fits of the model. The dotted arrow lines (magenta color) indicate estimated effective contrast ratios. Shaded areas represent ±1 Standard Error of the Mean (SEM) of the fits. The goodness-of-fit was assessed with the r2 statistic. (a) An individual with strabismic amblyopia (8 yrs, ET 6Δ, Fuses); (b) An individual with anisometropic amblyopia (9 yrs, ortho); (c) An individual with strabismus (7 yrs, XT 20Δ, Fuses); (d) A normally-sighted individual (7 yrs, ortho); (e) A normally-sighted individual (6 yrs, ortho); (f) A normally-sighted individual (5 yrs, ortho); (g) Correlation between effective contrast ratio and age (year). *ET: Esotropia, XT: Exotropia, Δ: Prism diopter, FU: Fuses, OD: Right eye, OS: Left eye. Note that the reported ocular deviation and fixational information are those made at near fixation (see Figs S1 and S2 for the data from all individual subjects).
Table 2.
Mean effective contrast ratio (η), mean parameter value γ and mean r2 value for the four subject groups.
Figure 3.
Mean effective contrast ratios for the four subject groups.
Mean effective contrast ratio as a function of subject group. Error bars represent ±1 Standard Errors of the Mean (SEM).
Figure 4.
Perceived phase plotted as a function of interocular contrast ratio for each subject group. The bootstrap resampling method [43] was performed to estimate the mean and standard errors of the data for each subject group. Each panel contains the average data (red circles) from each subject group. The average data were fitted with the attenuation model (Eq. 4) to obtain the effective contrast ratio of the weak eye. The black solid lines are the best fits of the model. The dotted arrow lines (magenta color) indicate estimated effective contrast ratios. Shaded areas represent ±1 SEM of the fits. The goodness-of-fit was evaluated by the r2 statistic: (a) Strabismic amblyopia; (b) Anisometropic amblyopia; (c) Strabismus; (d) Normal.
Figure 5.
Relationships between effective contrast ratio and clinical binocular function measures.
(a) Mean effective contrast ratios for four levels of IAD in logMAR units; (b) Mean effective contrast ratios for four levels of stereoacuity in acrsec units. Error bars represent ±1 SEM.
Figure 6.
(a) Correlation between 1st and 2nd tests. The dotted line indicates the line of equality (1st test = 2nd test). Each black dot indicates a data point from each subject; (b) Difference in ECR between 1st test and 2nd test as a function of mean value of the two tests. Each black dot indicates a data point from each subject. The horizontal red dashed line represents a bias of the test, i.e., the mean difference value across subjects. The horizontal black dotted lines represent 95% limits of agreement.