Objective vs subjective measures of fixation disparity for short and long fixation periods

Abstract

Subjective fixation disparity explained only about 25% of the inter-individual variability in objective fixation disparity. The discrepancy between these two measures might be explained by sensory shifts in retinal correspondence, also in the present condition without forced vergence.

Individual Differences in Binocular Coordination Are Uncovered by Directly Comparing Monocular and Binocular Reading Conditions

“…13 During monocular calibration of the eye movement recordings, binocular measures were stored while only one eye was fixated on the target. The resulting vergence angle without a fusion stimulus is known as heterophoria 24 (values included in Table 1).…”

Subjective Fixation Disparity Affected by Dynamic Asymmetry, Resting Vergence, and Nonius Bias

“…This correlation was also confirmed by objective measures. 22 2. Fixation disparity also correlates with binocular nonius bias.…”

“…14,24 Dynamic vergence step responses (both convergent and divergent) and heterophoria (during monocular calibration before and after each recording) were measured objectively using an eye-tracking system (EyeLink II; SR Research; Mississauga, Ontario, Canada), at 500 Hz, in the pupillary tracking mode. 22,24 The vergence stimuli were within the 40°horizontal gaze-tracking range. Despite the high physical precision of the system, its practical reliability is limited by the stability of head position: test-retest correlations of vergence velocity among different sessions were between 0.62 and 0.91; regarding the difference between velocity measures between two sessions, the range of Ϯ1.96 SD was Ϯ2.23 deg/s and Ϯ1.02 deg/s for the convergent and divergent velocity, respectively, as found in Bland-Altman plots (not shown).…”

“…This is not a measure of vergence but rather a measure of the nonius bias. 22 The run with all 40 trials took approximately 2 minutes.…”

Single vision during ocular deviation in intermittent exotropia

“…It has been proposed that anomalous retinal correspondence in constant strabismus reflects a remapping of the deviated eye onto primary visual cortex 1 . It has also been suggested that sensory shifts in retinal correspondence can occur in normal human subjects 66–68 …”