Making stereopsis related to the ability of ocular deviation: a new paradigm for assessment of intermittent exotropia

Abstract

Aim: To investigate the underlying factors by establishing a new paradigm for assessing control ability under stereopsis testing conditions.

Methods: This was a prospective observational study. We evaluated the control ability of intermittent exotropia (IXT) patients in three conditions: natural 2D optotype viewing, 2D optotype viewing with polarized glasses, and 3D optotype viewing with polarized glasses. Recording with a smartphone, we captured videos to analyze the accurate time of spontaneous exodeviation and subsequent realignment before and after breaking fusion. Additionally, the correlation of stereopsis were also analyzed.

Results: A total of 48 patients (age range: 4-33y; 54.17% male) participated in the study. When viewing 3D optotypes with polarized glasses, their median control scores were 1 (interquartile range, 0-4) at distance and 0 (0-1) at near. These scores were significantly better than those observed under natural viewing conditions, which were 2.5 (1-5) at a distance and 1 (0-3) at near (Friedman test, P=0.049). Furthermore, those subjects who exhibited exophoria (realignment within 2 seconds) while viewing 3D optotypes with polarized glasses were more likely to have measurable stereo vision (Kendall's τ_b=-0.344, P=0.018).

Conclusion: IXT patients exhibit enhanced control ability when using polarized glasses to view 3D optotypes, notably improving realignment capabilities. This expands our understanding of current tests and offers a potentially sensitive method for assessing IXT severity.

Keywords: control ability; intermittent exotropia; stereopsis.

Figure 1. The workflow of the novel paradigm

The same cohort underwent control ability assessments under three conditions. We used smartphones to capture videos of eye positions. We recorded and analyzed the spontaneous strabismus eye positions before covering or breaking fusion and the subsequent realignment.

Figure 2. Study design

Flowchart summarizing the study design and indicators used.

Figure 3. The control scores in each condition

A, B: Box and whiskers plots showing the control scores. Lines show upper quartile, median, and lower quartile values; C, D: The two segments of the arrow are the same subject, and the downward arrow indicates that the subject's control ability improved in condition 3. Con 1: Natural viewing condition; Con 2: Polarized glasses condition; Con 3: Polarized glasses + 3D optotype; Distance fixation (3 m); Near fixation (33 cm). ^aP<0.05; ^bP<0.01 after Bonferroni correction.

Figure 4. Analysis of recovery time in each condition

A-B: Box and whiskers plots showing the recovery time. Lines show upper quartile, median, and lower quartile values; C-D: The two segments of the arrow are the same subject, and the downward arrow indicates that the subject's recovery time decreased in the condition 3. Con 1: Natural viewing condition; Con 2: Polarized glasses condition; Con 3: Polarized glasses + 3D optotype; Distance fixation (3 m); Near fixation (33 cm). ^aP<0.05; ^bP<0.01 after Bonferroni correction.