Visual Therapy for Intermittent Strabismus

Official title

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

Overview

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.

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.

Interventions

• 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.

Primary outcome measures

• Change in Ocular Deviation [Time frame: Baseline (T0) to 12 weeks (T1)]
• Change in Binocular Function (Fusion and Stereopsis) [Time frame: Baseline (T0) to 12 weeks (T1)]
• Change in Strabismus Control [Time frame: Baseline (T0) to 12 weeks (T1)]
• Change in Vision-Related Quality of Life [Time frame: Baseline (T0) to 12 weeks (T1)]

Eligibility criteria

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

Criteria are shown verbatim from the registry (in English). Final eligibility is always assessed by the study center.

Healthy volunteers: No

Study design

Allocation

Randomized

Model

Parallel assignment

Masking

Single blind

Primary purpose

Treatment

Study locations

Center list to be confirmed — check the primary protocol.

Publications

• Sunyer-Grau B, Quevedo L, Rodriguez-Vallejo M, Argiles M. Comitant strabismus etiology: extraocular muscle integrity and central nervous system involvement-a narrative review. Graefes Arch Clin Exp Ophthalmol. 2023 Jul;261(7):1781-1792. doi: 10.1007/s00417-022-05935-9. Epub 2023 Jan 21. PMID 36680614
• Sunyer-Grau B, Quevedo L, Rodriguez-Vallejo M, Argiles M. Surgical outcomes and etiological considerations in intermittent exotropia: a systematic narrative review. Strabismus. 2025 Sep;33(3):188-198. doi: 10.1080/09273972.2024.2449563. Epub 2025 Jan 7. PMID 39773345
• Ma MM, Kang Y, Chen C, Su C, Tian Z, Le M. Vision therapy for intermittent exotropia: A case series. J Optom. 2021 Jul-Sep;14(3):247-253. doi: 10.1016/j.optom.2020.05.006. Epub 2020 Aug 12. PMID 32800454
• Pang Y, Gnanaraj L, Gayleard J, Han G, Hatt SR. Interventions for intermittent exotropia. Cochrane Database Syst Rev. 2021 Sep 13;9(9):CD003737. doi: 10.1002/14651858.CD003737.pub4. PMID 34516656
• Alvarez TL, Vicci VR, Alkan Y, Kim EH, Gohel S, Barrett AM, Chiaravalloti N, Biswal BB. Vision therapy in adults with convergence insufficiency: clinical and functional magnetic resonance imaging measures. Optom Vis Sci. 2010 Dec;87(12):E985-1002. doi: 10.1097/OPX.0b013e3181fef1aa. PMID 21057347
• Bui Quoc E, Milleret C. Origins of strabismus and loss of binocular vision. Front Integr Neurosci. 2014 Sep 25;8:71. doi: 10.3389/fnint.2014.00071. eCollection 2014. PMID 25309358

Identifiers

NCT: NCT07563959 · ViT(I)S

Primary sources (government registries)

• ClinicalTrials.gov (US NIH)

View this study on ClinicalTrials.gov ↗