Near Vergence Training for Distance Control in Intermittent Exotropia

Evaluating Near Vergence Training for Distance Control in Basic and Divergence Excess Intermittent Exotropia

Intermittent Exotropia (IXT) is a common type of eye misalignment where one eye periodically turns outward, and control is typically much worse when looking at objects far away than close up. However, most currently available training programme are focused on near-viewing tasks. The goal of this clinical trial is to investigate if a new, structured, home-based near eye training program works to improve distance eye alignment control in children and young adults with IXT.

The main questions the study aims to answer are:

• Does a 12-week near eye training program improve a participant's ability to control their eye alignment when looking at a distance?
• Does using a special reading glasses during near training help to control distance eye alignment better than doing the training without the reading glasses?
• Do the benefits of this eye training last after the training has stopped?

This is a two- phase, single- masked (examiner masked), randomized clinical trial with crossover design. The entire study duration is about 24 weeks. A total sample size of 42 participants, aged 6 to 25 years with diagnosed Basic (distance deviation is within 10 prism diopters of the near deviation) or Divergence excess (distance deviation is at least 10 prism diopters greater than the near deviation) IXT, will be recruited.

In Phase I (Weeks 0 to 12), participants will be randomly allocated into one of three groups, with 14 individuals in each group:

• Group 1 does eye training while wearing special plus-power reading glasses that remove the need to focus up close, mimicking how the eyes look at a distance.
• Group 2 does the exact same eye training but wears regular distance glasses without the special reading addition.
• Group 3 serves as a control group that does not do training during the first 12 weeks, but will receive the training in the second phase.

In Phase II (Weeks 13 to 24), which is a crossover phase, groups 1 and 2 will stop training to see if the visual improvements last, while group 3 will be re-randomized into two subgroups (group 3A, with special plus-power reading glasses, and group 3B with regular glasses with distance correction) that will undertake daily eye training for 12 weeks to ensure ethical treatment access. All participants will have a final eye exam at 24 weeks.

During home training, participants will:

• Wear standard glasses provided by the study.
• Practice daily, home-based eye exercises for 12 weeks using a standardized software program on a computer or tablet.
• Complete 3 training sessions every day, lasting 7 minutes per session.
• Wear red-blue 3D glasses during training and press arrow keys or swipe the screen to play a visual game that dynamically changes in difficulty.

Preliminary test and binocular vision assessment with fixed and uniform sequence will be performed at baseline visit, 6th week interim visit, 12th and 24th week evaluation. All eye examinations will be carried out in The Optometry Centre (A034), the School of Optometry, The Hong Kong Polytechnic University.

The following data will be statistically analyzed. The primary outcome data is distance Office Control Score (OCS) at 12-week visit. Secondary outcomes data include change in deviation angle, near and distance stereopsis and patient- / parent- reported health-related quality-of-life questions at 12-week.

Study Overview

• Status: Recruiting
• Conditions: Intermittent Exotropia
• Intervention / Treatment: Other: Home-based near eye training program

• Study Type: Interventional
• Enrollment (Estimated): 42
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: Horace Ho-yin Wong, MClinOptom, BSc (Hons) Optom; Phone Number: 852-63384048; Email: horace.wong@polyu.edu.hk
• Study Contact Backup: Name: Tsz Wing Leung, PhD; Phone Number: 852- 27664268; Email: jeffrey.TW.leung@polyu.edu.hk

Study Locations

• Hong Kong
  • Hong Kong, Hong Kong
    • Recruiting
    • The Optometry Clinic, The Hong Kong Polytechnic University
    • Contact: Horace Ho-yin Wong, MClinOptom, BSc (Hons) Optom; Phone Number: 852-63384048; Email: horace.wong@polyu.edu.hk

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Child; Adult
• Accepts Healthy Volunteers: No

Description

Inclusion Criteria

• Age and Diagnosis: Participants must be aged 6 to ≤ 25 years at the time of screening, with a confirmed clinical diagnosis of either Basic or Divergence Excess (DE) Intermittent Exotropia (IXT).
• Ocular Alignment Magnitude: Distance exodeviation measuring between 10 and 40 prism diopters (pd) inclusive, determined by the prism and alternate cover test (PACT).
• Distance-Near Disparity Limits: Near exodeviation must not exceed the distance exodeviation by more than 10 pd (to exclude Convergence Insufficiency type exotropia).
• Baseline Distance Control: A baseline distance IXT Office Control Score (OCS) between Grade 2 and Grade 4 inclusive, based on the mean of 3 standardized assessments.
• Baseline Near Control: A baseline near IXT control score less than or equal to the distance IXT control score, based on the mean of 3 standardized assessments.
• Visual Acuity: Best-corrected visual acuity (BCVA) of Logarithm of the Minimum Angle of Resolution (logMAR) 0.1 or better in each eye at both distance and near fixation.
• Sensory Status: Measurable near stereoacuity of 400 arc seconds or better on the Preschool Randot stereoacuity test.

• Refractive Correction Stability: Compliance with wearing a stable, appropriate spectacle correction for ≥ 4 months prior to formal baseline assessment if the participant meets any of the following refractive thresholds:

  • Myopia < -0.50D spherical equivalent (SE) in either eye.
  • Hyperopia > +2.50D SE in either eye.
  • Anisometropia > 1.00 SE.
  • Astigmatism > 1.50D cylinder in either eye.
• Treatment History: No history of prior non-surgical interventions for IXT, including patching, vision therapy/orthoptics, or overminus lens therapy (≥ 0.50 D).
• Surgical History: No prior history of strabismus surgery, extraocular muscle botulinum toxin injections, intraocular surgery, or refractive surgery.
• Trial Commitment: No planned strabismus surgery or conflicting ocular therapies during the 24-week study period.

Exclusion Criteria

• Amblyopia and Co-morbid Strabismus: Presence of amblyopia, nystagmus, restrictive strabismus, or paretic strabismus.
• Vertical Misalignment: Presence of an associated vertical ocular deviation > 5 pd.
• Significant Pathologies: Co-existing significant ocular disease or neurological disorders (e.g., cerebral palsy) that could confound oculomotor or sensory evaluations.
• Confounding Medications: Regular use of systemic or topical ocular medications known to alter accommodative or vergence function within the 3 months prior to screening (including, but not limited to, atropine, pirenzepine, or systemic anti-epileptic agents).

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: Triple

Number of Arms

3

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Active Comparator: Active training group with reading glasses; Receiving training in Phase I (Weeks 0 to 12), stop training in Phase II (Weeks 13 to 24) to study the effect persistence	Other: Home-based near eye training program; Standardized home-based near vergence training platform with data visualization tools and communication platforms
Active Comparator: Active training group without reading glasses; Receiving training in Phase I (Weeks 0 to 12), stop training in Phase II (Weeks 13 to 24) to study the effect persistence	Other: Home-based near eye training program; Standardized home-based near vergence training platform with data visualization tools and communication platforms
No Intervention: Control group; No training will be received in Phase I (Weeks 0 to 12); Will receive training in Phase II of the study (Weeks 13 to 24) to ensure ethical treatment access

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Change of Distance Office Control Score	Objective and quantitative office control scale, based on the frequency of deviation and the recovery speed followed by occlusion. Ranged from 0 to 5, with score 0 represents the best control (phoria with excellent control), and score 5 represents the worst control (constant exotropia during the 30-second observation)	Baseline, 6-week, 12-week and 24-week

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Change of exodeviation magnitude angle	measured by Prism and Alternate Cover Test, ranged from 1 to 50 prism diopter. The higher the value, the worse is the magnitude angle of the exodeviation	Baseline, 6-week, 12-week and 24-week
Change of Distance stereoacuity	measured by Distance Randot® stereotest, ranged from 400 seconds of arc (the worst measurable stereoacuity) to 60 seconds of arc (the best measurable stereoacuity )	Baseline, 6-week, 12-week and 24-week
Change of Near stereoacuity	measured by Preschool Randot® stereoacuity test, ranged from 800 seconds of arc (the worst measurable stereoacuity) to 40 seconds of arc (the best measurable stereoacuity )	Baseline, 6-week, 12-week and 24-week
Change of Quality of Life (QoL) measures - Chinese Intermittent Exotropia Questionnaire (CIXTQ) for children aged 5 to 17 and parents of children aged 2 to 17	Part a: Child CIXTQ - 12 items completed by children, simplified 3-point scale (0, 50 and 100); Part b: Proxy CIXTQ - 12 items completed by parents to evaluate their child's health-related quality-of-life (HRQoL) from a parental perspective, 5-point Likert-type (0, 25, 50, 75, and 100); Part c: Parent CIXTQ - 17 items to measure the parent's own HRQoL, 5-point Likert-type (0, 25, 50, 75 and 100). The higher the score, the better the outcome (QoL).	Baseline, 12-week and 24-week
Change of Quality of Life (QoL) measures - The Chinese Adult Strabismus Quality of Life Questionnaire (CAS-20) for adult participants aged 18 or above	20 items to assess psychosocial impact and visual function, 5-point Likert-type (0, 25, 50, 75 and 100). Higher scores indicating better perceived QoL.	Baseline, 12-week and 24-week

Collaborators and Investigators

• Sponsor: The Hong Kong Polytechnic University

Publications and helpful links

General Publications

• Mohney BG, Holmes JM. An office-based scale for assessing control in intermittent exotropia. Strabismus. 2006 Sep;14(3):147-50. doi: 10.1080/09273970600894716.
• Ma MM, Kang Y, Scheiman M, Chen Q, Ye X, Pan L, Deng J, Su G, Zhang G, Chen X. Office-based vergence and anti-suppression therapy for the treatment of small-to-moderate angle intermittent exotropia: A randomised clinical trial. Ophthalmic Physiol Opt. 2024 Mar;44(2):356-377. doi: 10.1111/opo.13264. Epub 2023 Dec 26.

Study record dates

Study Major Dates

• Study Start (Estimated): June 1, 2026
• Primary Completion (Estimated): June 1, 2028
• Study Completion (Estimated): December 1, 2028

Study Registration Dates

• First Submitted: June 3, 2026
• First Submitted That Met QC Criteria: June 10, 2026
• First Posted (Actual): June 11, 2026

Study Record Updates

• Last Update Posted (Actual): June 11, 2026
• Last Update Submitted That Met QC Criteria: June 10, 2026
• Last Verified: May 1, 2026

More Information

Terms related to this study

• Other Study ID Numbers: HSEARS20251213004

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: UNDECIDED

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No