Visual Therapy for Intermittent Strabismus (ViT(I)S)

April 26, 2026 updated by: Laura Asensio Jurado, Universitat Politècnica de Catalunya

Efficacy of Visual Therapy in Intermittent Non-Pathological Horizontal Strabismus: A Randomized Controlled Trial

Intermittent strabismus is a condition in which the eyes occasionally become misaligned, affecting binocular vision, depth perception, and quality of life. Standard treatment often involves surgery of the eye muscles, although its effectiveness and timing remain debated.

Visual therapy is a non-invasive alternative that uses structured exercises to improve eye coordination and binocular vision. However, there is limited high-quality evidence supporting its effectiveness in intermittent strabismus.

This randomized controlled trial aims to evaluate whether a 12-session visual therapy program improves eye alignment, binocular vision, control of strabismus, and quality of life in individuals aged 8 to 50 years with intermittent horizontal strabismus.

Participants will be assigned to either a visual therapy group or a control group without treatment. Visual therapy will include weekly in-office sessions combined with short daily home exercises.

The study will assess changes before and after the intervention to determine whether visual therapy is an effective, non-invasive treatment option that could reduce the need for surgery.

Study Overview

Status

Not yet recruiting

Conditions

Intervention / Treatment

Detailed Description

Strabismus is a heterogeneous condition that may arise from alterations in extraocular muscles, their innervation, or central nervous system mechanisms. In this study, strabismus refers specifically to intermittent horizontal strabismus not associated with ocular, systemic, or neurological pathology, nor with orbital or craniofacial abnormalities.

Surgical correction of extraocular muscles is currently the main treatment approach. However, controversy exists regarding surgical indications, timing, and long-term outcomes. Furthermore, growing evidence suggests that many cases of strabismus may be related to central nervous system dysfunction rather than primary muscular abnormalities.

Visual therapy (VT) is a non-invasive intervention consisting of structured exercises designed to improve oculomotor control and enhance sensory and motor fusion. Neuroimaging studies have demonstrated central nervous system changes following VT in conditions such as convergence insufficiency, supporting its potential mechanism of action.

Despite these findings, evidence supporting VT for intermittent strabismus remains limited and is primarily based on case series and retrospective studies. Therefore, a prospective, randomized controlled trial is needed.

This study is a single-center, prospective, randomized, controlled, single-masked clinical trial conducted at Hospital Universitari Mútua de Terrassa.

Participants aged 8 to 50 years with intermittent horizontal strabismus will be recruited and randomly assigned to:

Experimental group: visual therapy Control group: no treatment during the study period

The intervention will consist of 12 weekly in-office sessions (1 hour each) at the Centre Universitari de la Visió, combined with daily home-based exercises (~10 minutes), with adherence monitoring.

Outcome assessments will be conducted at baseline (T0) and post-treatment (T1) using standardized optometric procedures. Outcome assessors will be masked to group allocation to minimize bias.

Primary outcomes include changes in ocular deviation measured using alternate cover test with prism bars and Hirschberg test. Secondary outcomes include binocular function (fusion and stereopsis), control of deviation (Mohney and Holmes Office Control Score), and vision-related quality of life (AS-20 for adults and IXTQ for children).

Statistical analysis will compare pre- and post-intervention changes between groups using repeated measures models or equivalent non-parametric tests where appropriate.

The intervention poses minimal risk, as it is non-invasive and does not involve pharmacological treatment. Potential risks are limited to mild visual fatigue or unmet expectations, which will be mitigated through appropriate participant information.

This study aims to determine whether visual therapy can serve as an effective, non-invasive treatment for intermittent strabismus and potentially reduce the need for surgical intervention.

Study Type

Interventional

Enrollment (Estimated)

30

Phase

  • Not Applicable

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Contact

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

  • Child
  • Adult

Accepts Healthy Volunteers

No

Description

Inclusion Criteria:

Individuals aged 8 to 50 years Diagnosis of intermittent horizontal strabismus (exotropia or esotropia) Absence of associated ocular, systemic, or neurological pathology Ability to understand and follow study instructions Willingness and motivation to complete 12 sessions of visual therapy (for the experimental group) Written informed consent (and assent for minors when applicable)

Exclusion Criteria:

Previous visual therapy treatment Inability to attend in-office visual therapy sessions Presence of ocular, systemic, or neurological disease affecting vision Constant strabismus Cognitive or intellectual impairment limiting the ability to perform the exercises

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

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

Arms and Interventions

Participant Group / Arm
Intervention / Treatment
Experimental: Visual Therapy
Participants will receive a structured visual therapy program consisting of 12 weekly in-office sessions (1 hour each) combined with daily home-based exercises (~10 minutes), with adherence monitoring.
Behavioral: Visual Therapy
A structured program of visual exercises designed to improve oculomotor control and binocular vision. The intervention includes 12 weekly in-office sessions (1 hour each) conducted at a specialized center, combined with daily home-based exercises (~10 minutes), with adherence monitoring.
No Intervention: Control
Participants will not receive any intervention during the study period. They will undergo the same baseline and post-study assessments as the experimental group.

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Change in Ocular Deviation
Time Frame: Baseline (T0) to 12 weeks (T1)
Ocular deviation will be assessed using the alternate cover test with prism bars in primary gaze and Hirschberg test with image capture. The magnitude of deviation will be expressed in prism diopters (PD).
Baseline (T0) to 12 weeks (T1)
Change in Binocular Function (Fusion and Stereopsis)
Time Frame: Baseline (T0) to 12 weeks (T1)
Binocular function will be assessed using the Worth 4 Dot test (fusion) and stereopsis tests at near distance.
Baseline (T0) to 12 weeks (T1)
Change in Strabismus Control
Time Frame: Baseline (T0) to 12 weeks (T1)
Control of strabismus will be assessed using the Mohney and Holmes Office Control Score, a 5-point ordinal scale evaluating the frequency and control of ocular deviation.
Baseline (T0) to 12 weeks (T1)
Change in Vision-Related Quality of Life
Time Frame: Baseline (T0) to 12 weeks (T1)
Quality of life will be assessed using validated questionnaires: AS-20 for adults and Intermittent Exotropia Questionnaire (IXTQ) for pediatric participants.
Baseline (T0) to 12 weeks (T1)

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

Universitat Politècnica de Catalunya

Collaborators

Hospital Universitari Mútua de Terrassa

Publications and helpful links

The person responsible for entering information about the study voluntarily provides these publications. These may be about anything related to the study.

General Publications

  • Sunyer-Grau, B., Quevedo, L., Rodríguez-Vallejo, M., & Argilés, M. (2023). Comitant strabismus etiology: extraocular muscle integrity and central nervous system involvement-a narrative review. Graefe's archive for clinical and experimental ophthalmology = Albrecht von Graefes Archiv fur klinische und experimentelle Ophthalmologie, 261(7), 1781-1792. https://doi.org/10.1007/s00417-022-05935-9
  • Sunyer-Grau, B., Quevedo, L., Rodríguez-Vallejo, M., & Argilés, M. (2025). Surgical outcomes and etiological considerations in intermittent exotropia: a systematic narrative review. Strabismus, 33(3), 188-198. https://doi.org/10.1080/09273972.2024.2449563
  • Ma MM, Kang Y, Chen C, Su C, Tian Z, Le M. Vision therapy for intermittent exotropia: A case series. J Optom. 2021;14(3):247-253. doi:10.1016/j.optom.2020.05.006
  • Pang, Y., Gnanaraj, L., Gayleard, J., Han, G., & Hatt, S. R. (2021). Interventions for intermittent exotropia. The Cochrane database of systematic reviews, 9(9), CD003737. https://doi.org/10.1002/14651858.CD003737.pub4
  • Alvarez TL, Vicci VR, Alkan Y, et al. Vision therapy in adults with convergence insufficiency: clinical and functional magnetic resonance imaging measures. Optom Vis Sci. 2010;87(12):E985-E1002. doi:10.1097/OPX.0b013e3181fef1aa
  • Bui Quoc E, Milleret C. Origins of strabismus and loss of binocular vision. Front Integr Neurosci. 2014;8:71. Published 2014 Sep 25. doi:10.3389/fnint.2014.00071

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Estimated)

May 1, 2026

Primary Completion (Estimated)

July 1, 2028

Study Completion (Estimated)

July 1, 2028

Study Registration Dates

First Submitted

April 26, 2026

First Submitted That Met QC Criteria

April 26, 2026

First Posted (Actual)

May 4, 2026

Study Record Updates

Last Update Posted (Actual)

May 4, 2026

Last Update Submitted That Met QC Criteria

April 26, 2026

Last Verified

April 1, 2026

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

  • ViT(I)S

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

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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