An interventional study of Attention-Guided Dichoptic Visual Search Training and Zero-Disparity Dichoptic Visual Search Task in Amblyopia, Strabismus and Anisometropia, sponsored by Centre for Eye and Vision Research. Not yet recruiting at 2 sites in Hong Kong. Open to participants aged 18 Years to 39 Years, including healthy volunteers. Per ClinicalTrials.gov, last updated 2026-09-03.
Sponsored by Centre for Eye and Vision Research · Not applicable, Interventional, and Treatment
This study evaluates a novel attention-based binocular visual search training paradigm designed to improve stereopsis (stereo vision) in individuals with impaired binocular vision. Disruptions in balanced binocular input, such as from strabismus or anisometropia, often lead to deficient stereo vision, causing daily visuomotor limitations. While traditional therapies focus on monocular acuity, they frequently fail to restore stereopsis, especially in adults. The investigators propose a unique dichoptic visual search training method that embeds binocular disparity inside an attention-demanding task, encouraging cooperative binocular integration. Participants aged 18-39 with impaired stereopsis will be randomly assigned in a 1:1 ratio to either the active training group (disparity-embeded task) or the active control group (identical task with zero disparity). Both groups complete 5 training sessions over 5-6 weeks. Assessments will occur at baseline, immediately post-training, and at a 12-week follow-up. The primary objective is to determine if the active training group shows significantly greater improvements in local stereoacuity compared to the control group.
189 studies on the registry are indexed under Amblyopia; 41 are open to participants now.
This study's planned enrollment of 56 is close to the median of 60 across 137 interventional studies indexed under Amblyopia.
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Participants complete a dichoptic visual search task where the search target is uniquely paired with crossed binocular disparity under balanced interocular contrast. The training consists of 5 sessions (5 blocks of 192 trials per session) over 5-6 weeks with adaptive disparity adjustment.
Behavioral: Attention-Guided Dichoptic Visual Search Training
Participants perform an identical computer-based dichoptic visual search task with the same geometric stimuli, trial structure (5 blocks of 192 trials per session), and interocular contrast balancing, but with zero binocular disparity.
Behavioral: Zero-Disparity Dichoptic Visual Search Task
A computer-based dichoptic training paradigm in which visual stimuli are presented separately to each eye under balanced interocular contrast . Participants search for conjunction-defined targets across 5 sessions (5 blocks of 192 trials per session). The target stimulus is uniquely paired with crossed binocular disparity to provide depth-based attentional guidance, with target disparity adaptively reduced based on search performance.
An active control dichoptic task identical in visual stimuli, trial structure (5 sessions; 5 blocks of 192 trials per session), and interocular contrast balancing to the training arm, but presented with zero binocular disparity (all stimuli appear in the same depth plane without depth cues).
Change in Local Stereoacuity
Measured using the Randot Stereotest - Circles test (graded disparities from 400 to 20 arcsec, 10 levels) under standardized lighting at 40 cm. The score is recorded as the finest disparity correctly identified (in log arcseconds). Nil stereopsis is assigned 3000 arcsec (3.477 log arcsec). The primary metric is the between-group difference in the change score.
Time frame: Baseline (T0) and Immediately Post-Training (T1, within 7 days after Session 5, approximately 5-6 weeks from baseline).
Retention of Local Stereoacuity Gains
Measured using the Randot Stereotest - Circles test under crossed disparity (log10 arcsec; nil stereopsis assigned 3000 arcsec) to evaluate long-term maintenance of training effects
Time frame: Baseline (T0), Immediately Post-Training (T1), and 12-Week Follow-Up (T2).
Change in Uncrossed Local Stereoacuity
Measured using the Randot Stereotest - Circles test with the test booklet rotated 180 degrees (log10 arcsec; nil stereopsis assigned 3000 arcsec).
Time frame: Baseline (T0), Immediately Post-Training (T1), and 12-Week Follow-Up (T2).
Change in Global Stereoacuity
Measured with the Randot Preschool Stereotest (random-dot stereograms, 800 to 40 arcsec, 6 levels) under both crossed and uncrossed disparity conditions (log10 arcsec; nil stereopsis assigned 3000 arcsec).
Time frame: Baseline (T0), Immediately Post-Training (T1), and 12-Week Follow-Up (T2).
Change in Laboratory-Based Stereoacuity Threshold
Psychophysical stereoacuity threshold (75% threshold in log10 arcsec) measured using a 4-alternative forced-choice staircase ring test administered dichoptically.
Time frame: Baseline (T0), Immediately Post-Training (T1), and 12-Week Follow-Up (T2).
Change in Best-Corrected Visual Acuity (BCVA)
Monocular (affected/dominant eyes) and binocular distance visual acuity measured using an electronic ETDRS logMAR chart at 4 meters (recorded in logMAR units).
Time frame: Baseline (T0), Immediately Post-Training (T1), and 12-Week Follow-Up (T2).
Change in Interocular Suppression Status
Binocular status classified into categorical states (fusion, suppression, or diplopia) using the Worth 4-dot test at near (40 cm) and distance (3 m).
Time frame: Baseline (T0), Immediately Post-Training (T1), and 12-Week Follow-Up (T2).
Change in Interocular Suppression Strength (Contrast Balance Ratio)
Effective suppression depth quantified by the interocular contrast ratio at the perceptual balance point measured via a dichoptic letter-polarity task.
Time frame: Baseline (T0), Immediately Post-Training (T1), and 12-Week Follow-Up (T2).
Change in Visual Evoked Potentials (VEPs)
Peak latencies (ms) and amplitudes (μV) of the transient pattern-reversal VEP N75-P100-N135 complex across high-contrast and isoluminant red-green conditions, alongside harmonic amplitudes/phases (2F, 4F) from steady-state VEPs, recorded via a 64-channel EEG system.
Time frame: Baseline (T0), Immediately Post-Training (T1), and 12-Week Follow-Up (T2).
Change in Electrophysiological Marker of Attentional Selection (N2pc Component)
Mean amplitude (μV) of the posterior contralateral-minus-ipsilateral difference wave (N2pc) extracted across predefined parieto-occipital electrodes (P7, PO7, P8, PO8) during a modified spatial cueing task.
Time frame: Baseline (T0), Immediately Post-Training (T1), and 12-Week Follow-Up (T2).
Change in Behavioral Selective Attention
Spatial cueing effects on mean reaction time (ms) and response accuracy (%) derived from the modified spatial cueing task.
Time frame: Baseline (T0), Immediately Post-Training (T1), and 12-Week Follow-Up (T2).
Change in Visual Search Efficiency
Visual search slope (reaction time as a function of set size, in ms/item) measured from a 192-trial zero-disparity dichoptic visual search task.
Time frame: Baseline (T0), Immediately Post-Training (T1), and 12-Week Follow-Up (T2).
Change in Visuomotor Coordination Completion Time and Kinematic Parameters
Visuomotor dexterity and kinematic performance are assessed using the Grooved Pegboard Test separately for dominant and non-dominant hands. Hand movements during the task are video recorded for detailed kinematic tracking. The primary quantitative metric for this outcome is the total completion time (in seconds) required to successfully place all 25 grooved pegs (shorter duration indicates better motor speed and coordination). Secondary kinematic metrics extracted from video analyses include mean peg-insertion duration (seconds), inter-peg temporal variability across the 25 trials (coefficient of variation, CV), and total drop/error counts.
Time frame: Baseline (T0), Immediately Post-Training (T1), and 12-Week Follow-Up (T2).
Change in Quality of Life Scores
Domain scores assessed via the World Health Organization Quality of Life Instrument-Short Form (WHO QoL-BREF) and the Amblyopia and Strabismus Questionnaire (A\&SQ). Higher scores indicate superior functional visual ability and quality of life. For both questionnaires, domain and composite scores are linearly transformed to a standardized 0 to 100 scale, where higher scores represent superior functional visual ability, fewer daily limitations, and better overall quality of life.
Time frame: Baseline (T0), Immediately Post-Training (T1), and 12-Week Follow-Up (T2).
Plan to share: Yes — Anonymized data will be shared on request.
Supporting information: Study protocol, Statistical analysis plan
Time frame: After publication of study results for an indefinite period.
Access criteria: Upon reasonable request and approved by the study principal investigator.
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