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.

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.

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

Outcome assessors (optometrists) will be masked to group allocation. Participants and care providers cannot be masked due to the nature of the intervention.