Amblyopia, Anisometropia, Binocular Vision Abnormalities, Binocular Vision Disorder, Strabismus
Conditions
Keywords
Stereopsis, Depth Perception, Visual Search, Visual Attention, Dichoptic Training
Brief summary
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.
Interventions
BEHAVIORALAttention-Guided Dichoptic Visual Search Training
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.
BEHAVIORALZero-Disparity Dichoptic Visual Search Task
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).
Sponsors
Centre for Eye and Vision Research
The Hong Kong Polytechnic University
University of Waterloo
Study design
Allocation
RANDOMIZED
Intervention model
PARALLEL
Primary purpose
TREATMENT
Masking
SINGLE (Outcomes Assessor)
Eligibility
Sex/Gender
ALL
Age
18 Years to 39 Years
Healthy volunteers
Yes
Inclusion criteria
* Aged 18-39 years (inclusive). * Deficient or anomalous stereoscopic vision with a stereoacuity \>= 70 sec arc or unmeasurable stereoacuity. * Best corrected visual acuity (BCVA) of \< 0.80 logMAR in both eyes, with at least one eye having a visual acuity of \<= 0.1 logMAR (uncorrected or corrected-to-normal with glasses or contact lenses). * Normal colour vision. * Good general health.
Exclusion criteria
* Previous history of ocular surgery (except for refractive correction surgery, where appropriate). * Pre-existing ocular conditions or medications that affect vision or visual function. * Pre-existing conditions or medications that affect neuropsychological function. * Presence of strabismus over 10 prism diopters at distance in current refractive correction measured by simultaneous prism and cover test, or large eccentric fixation. * Previous history of experiencing double vision (diplopia). * Identified at risk of developing diplopia due to binocular state and/or poor binocular control. * Inability to comprehend psychophysical test instructions given and/or consent for themselves.
Design outcomes
Primary
| Measure | Time frame | Description |
|---|---|---|
| Change in Local Stereoacuity | Baseline (T0) and Immediately Post-Training (T1, within 7 days after Session 5, approximately 5-6 weeks from baseline). | 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. |
Secondary
| Measure | Time frame | Description |
|---|---|---|
| Retention of Local Stereoacuity Gains | Baseline (T0), Immediately Post-Training (T1), and 12-Week Follow-Up (T2). | 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 |
| Change in Uncrossed Local Stereoacuity | Baseline (T0), Immediately Post-Training (T1), and 12-Week Follow-Up (T2). | Measured using the Randot Stereotest - Circles test with the test booklet rotated 180 degrees (log10 arcsec; nil stereopsis assigned 3000 arcsec). |
| Change in Global Stereoacuity | Baseline (T0), Immediately Post-Training (T1), and 12-Week Follow-Up (T2). | 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). |
| Change in Laboratory-Based Stereoacuity Threshold | Baseline (T0), Immediately Post-Training (T1), and 12-Week Follow-Up (T2). | Psychophysical stereoacuity threshold (75% threshold in log10 arcsec) measured using a 4-alternative forced-choice staircase ring test administered dichoptically. |
| Change in Best-Corrected Visual Acuity (BCVA) | Baseline (T0), Immediately Post-Training (T1), and 12-Week Follow-Up (T2). | Monocular (affected/dominant eyes) and binocular distance visual acuity measured using an electronic ETDRS logMAR chart at 4 meters (recorded in logMAR units). |
| Change in Interocular Suppression Status | Baseline (T0), Immediately Post-Training (T1), and 12-Week Follow-Up (T2). | Binocular status classified into categorical states (fusion, suppression, or diplopia) using the Worth 4-dot test at near (40 cm) and distance (3 m). |
| Change in Interocular Suppression Strength (Contrast Balance Ratio) | Baseline (T0), Immediately Post-Training (T1), and 12-Week Follow-Up (T2). | Effective suppression depth quantified by the interocular contrast ratio at the perceptual balance point measured via a dichoptic letter-polarity task. |
| Change in Visual Evoked Potentials (VEPs) | Baseline (T0), Immediately Post-Training (T1), and 12-Week Follow-Up (T2). | 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. |
| Change in Electrophysiological Marker of Attentional Selection (N2pc Component) | Baseline (T0), Immediately Post-Training (T1), and 12-Week Follow-Up (T2). | 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. |
| Change in Behavioral Selective Attention | Baseline (T0), Immediately Post-Training (T1), and 12-Week Follow-Up (T2). | Spatial cueing effects on mean reaction time (ms) and response accuracy (%) derived from the modified spatial cueing task. |
| Change in Visual Search Efficiency | Baseline (T0), Immediately Post-Training (T1), and 12-Week Follow-Up (T2). | 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. |
| Change in Visuomotor Coordination Completion Time and Kinematic Parameters | Baseline (T0), Immediately Post-Training (T1), and 12-Week Follow-Up (T2). | 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. |
| Change in Quality of Life Scores | Baseline (T0), Immediately Post-Training (T1), and 12-Week Follow-Up (T2). | 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. |
Countries
Hong Kong
Contacts
CONTACTJeffrey TW Leung, PhD
CONTACTBenjamin Thompson, PhD
Outcome results
None listed