Evaluating Eye Tracking During Dichoptic Video Viewing With Varied Fellow Eye Contrasts in Amblyopia

Abstract

Purpose: This study uses eye tracking to investigate how varying fellow eye (FE) contrast during dichoptic video viewing influences eye movement patterns, and their associations with interocular suppression, visual acuity, and stereoacuity deficit in amblyopia.

Methods: Eye movements of 27 amblyopic and 8 healthy control participants were recorded during dichoptic viewing of stationary dots and videos with FE contrasts (100%, 50%, 25%, and 10%). Analysis included durations the amblyopic and FE spent in different stimulus regions, fixation switches, and eye deviation, and correlating these with suppression, visual acuity, and stereoacuity.

Results: Participants with pronounced suppression, visual acuity, and stereoacuity deficits demonstrated reduced amblyopic eye fixation in the amblyopic eye (AE) region at 100% FE contrast. Lowering FE contrast increased amblyopic eye duration in stimuli presented within the AE region, notably in anisometropic and treated strabismic participants, and strabismic participants exhibiting fixation switches during viewing of dichoptic stationary dots. Even at lower FE contrasts, participants with greater stereoacuity and visual acuity deficits continued to exhibit diminished AE fixation in the AE region. Increased eye deviation was seen in strabismic participants with lowering of FE contrasts.

Conclusions: Dichoptic contrast modulation holds promise for reducing suppression with responses varying by amblyopia type and visual function deficits. Larger strabismic angles may hinder binocular benefits of dichoptic treatments. Fixation switches may serve as an indicator of favorable outcomes. Eye tracking is crucial for understanding these dynamics, providing essential insights into visual attention dynamics of the FE and AE, and may serve as a valuable tool in optimization of amblyopia treatments.

Figure 1.

(A) Shows a sample videoframe of the dichoptic stimulus presented to both amblyopic eye and fellow eye. The amblyopic eye stimulus contains the amblyopic eye (AE) region of the dichoptic stimulus that is visible only to the amblyopic eye. The fellow eye stimulus contains the fellow eye (FE) region of the dichoptic stimulus that is visible only to the fellow eye. The transition region indicates the regions of transition from an AE region to an FE region and is visible to both eyes albeit at different contrast levels. (B) illustrates how the image will appear to participants who are able to perceive the stimulus presented to the fellow eye and amblyopic eye simultaneously during dichoptic viewing (in other words, the participant must be able to combine the stimuli presented to the fellow eye [FE region] and amblyopic eye [AE region] together to appreciate the entire image). It also has eye positions overlaid for controls (green), anisometropic (yellow), < 5Δ (blue), and > 5Δ (red) strabismic participants on the stimulus as color filled circles to demonstrate amblyopic eye and fellow eye (black edges) fixations within that videoframe. Examples of fixations in synchronous time, where both eyes are in the same region, asynchronous time, where each eye is within the video frame but are in different regions, and asynchronous time out, where only one eye is within the video frame while the other eye is outside the video frame are marked with their respective signs.

Figure 2.

Epoch of eye positions acquired over a 10 second period while watching dichoptic video clip from one subject. The plot shows filtered gaze coordinates (black) measured in degrees and eye movement events segmentation with periods of fixation (cream), pursuit (brown), and saccades (light green), as detected using REMoDNaV algorithm.

Figure 3.

Depicts the temporal synchronization of both eyes in terms of percentage durations spent in each of the three classifications at each FE contrast level (A) 100% FE, (B) 50% FE, (C) 25% FE, and (D) 10% FE, for each of the four groups. Controls (green), anisometropia (yellow), < 5Δ (blue), and > 5Δ (red). Asterisk (*) indicates statistically significant difference between groups evaluated at P < 0.05 for post hoc multiple pairwise comparisons with Bonferroni correction.

Figure 4.

Illustrates fixation behavior of participants 7 and 8 (anisometropic amblyopia) during the viewing of dichoptic videos. The snapshots were taken at each FE contrast level and overlaid with amblyopic eye and fellow eye positions. Subject 7 is fixating with both eyes on the stimulus presented to the fellow eye (FE region) at 100%, 50%, and 25% FE contrasts but fixates on stimulus presented to amblyopic eye (AE region) at 10% FE contrast. Subject 8, however, fixates on the stimulus presented in the fellow eye (FE region) only at 100% FE contrast but fixates on the stimulus presented in the amblyopic eye (AE region) at 50%, 25%, and 10% FE contrasts. = synchronous time (amblyopic eye and fellow eye are in the same region). Fixation of the amblyopic eye within the amblyopic eye stimulus region is indicated by a red arrow pointing to the gaze position with a red shape surrounding the gaze position whereas fixation of the fellow eye within the fellow eye stimulus region is indicated by a black arrow pointing to the gaze position with a black shape surrounding the gaze position.

Figure 5.

Illustrates fixation behavior participants 11 and 12 (strabismic (< 5Δ) amblyopia participants) during viewing of dichoptic videos. Their fellow eye and amblyopic eye positions are overlaid on a video frame from each contrast of the dichoptic videos. Subject 11 has amblyopic eye fixing in the FE or transition region and not in the AE region for all 4 contrasts. Subject 12 had amblyopic eye fixing in the AE regions at 25% and 10% FE contrasts. = synchronous time (amblyopic eye and fellow eye are in the same region); = asynchronous time (amblyopic eye and fellow eye in different regions on the stimulus). Fixation of the amblyopic eye within the amblyopic eye stimulus region is indicated by a red arrow pointing to the gaze position with a red shape surrounding the gaze position whereas fixation of the fellow eye within the fellow eye stimulus region is indicated by a black arrow pointing to the gaze position with a black shape surrounding the gaze position.

Figure 6.

Illustrates fixation switch behavior of subjects 19 and 23 (strabismic > 5Δ amblyopia participants) during viewing of dichoptic videos. Their fellow eye and amblyopic eye positions are overlaid on a video frame from each contrast of the dichoptic videos. Subject 19 had their fellow eye fixating in the FE region at 100% FE contrast and amblyopic eye outside the video frame. However, at 50%, 25%, and 10% FE contrasts, the amblyopic eye is fixating in the AE regions and fellow eye is outside the video frame. Subject 23 has the amblyopic eye fixating outside of the video frame while fellow eye is fixating in the FE region or transition region and not in the AE region for all 4 FE contrasts. Fixation of the amblyopic eye within the amblyopic eye stimulus region is indicated by a red arrow pointing to the gaze position with a red shape surrounding the gaze position whereas fixation of the fellow eye within the fellow eye stimulus region is indicated by a black arrow pointing to the gaze position with a black shape surrounding the gaze position. △ = asynchronous out (one eye on the screen and the other eye outside the video frame).

Figure 7.

Illustrations of percentage durations both the fellow eye and amblyopic eye spent within each of the four regions (FE, AE, transitions regions, and outside) at each FE contrast level (A) 100% FE, (B) 50% FE, (C) 25% FE, and (D) 10% FE, for each of the 4 groups. Controls (green), anisometropia (yellow), < 5Δ (blue), and > 5Δ (red). Asterisk (*) indicates statistically significant difference between groups evaluated at P < 0.05 for post hoc multiple pairwise comparisons with Bonferroni correction.

Figure 8.

Depicts cumulative sum histograms of eye deviations (degrees) at each contrast level (FE 100%, FE 50%, FE 25%, and FE 10%) for each group for both stationary dot (dotted lines) and dichoptic videos (solid lines) trials. (A) Controls (green), (B) anisometropia (yellow), (C) < 5Δ (blue), and (D) > 5Δ (red). The colors are shaded to show a reduction in FE contrasts within each group. DM = dichoptic video stimuli; DG = dichoptic stationary dot stimuli.