A Comparative Study of Fusional Vergence According to Ocular Dominance in Healthy Subjects (ECAFOSS)

July 6, 2026 updated by: Assistance Publique - Hôpitaux de Paris

In orthoptics, fusional vergence (FV) measurement is one of the key tests used to assess fusion ability. These amplitudes are generally reduced in individuals with convergence insufficiency. Fusional vergence are quantified by placing a prism bar randomly in front of one eye-first for distance vision and then for near vision. Rehabilitation exercises using the prism bar are also performed in the same manner.

Depending on orthoptic practice, the prism bar is placed in front of the left eye or the right eye, in a dogmatic manner, or in front of the right eye, in a conventional manner, without any study providing any justification. However, some practitioners report interocular differences when measuring fusion amplitudes depending on which eye is prismed, while others do not.

The hypothesis put forward is that, in individuals with an interocular difference in fusional vergence, ocular dominance (sensory and motor) could be the cause of this measurement discrepancy.

The objective is therefore to compare the difference in fusional vergence depending on whether the dominant or non-dominant eye is tested, using a randomized order of eyes and tests.

If this hypothesis is confirmed (greater fusional vergence when tested on the dominant eye), this would: (1) enhance our understanding of fusion mechanisms, (2) provide more targeted insights for the assessment, quantification, and rehabilitation of fusional vergence to improve the effectiveness of orthoptic intervention.

Study Overview

Status

Not yet recruiting

Conditions

Intervention / Treatment

Detailed Description

In orthoptics, fusional vergence (FV) measurement is one of the key tests used to assess fusion ability. These amplitudes are generally reduced in individuals with convergence insufficiency. Fusional vergence are quantified by placing a prism bar randomly in front of one eye-first for distance vision and then for near vision. Rehabilitation exercises using the prism bar are also performed in the same manner.

Depending on orthoptic practice, the prism bar is placed in front of the left eye or the right eye, in a dogmatic manner, or in front of the right eye, in a conventional manner, without any study providing any justification. However, some practitioners report interocular differences when measuring fusion amplitudes depending on which eye is prismed, while others do not.

The hypothesis put forward is that, in individuals with an interocular difference in fusional vergence, ocular dominance (sensory and motor) could be the cause of this measurement discrepancy.

The objective is therefore to compare the difference in fusional vergence depending on whether the dominant or non-dominant eye is tested, using a randomized order of eyes and tests.

If this hypothesis is confirmed (greater fusional vergence when tested on the dominant eye), this would: (1) enhance our understanding of fusion mechanisms, (2) provide more targeted insights for the assessment, quantification, and rehabilitation of fusional vergence to improve the effectiveness of orthoptic intervention.

The study consists of one-hour eye examinations of healthy individuals with no visual or oculomotor disorders.

Study Type

Observational

Enrollment (Estimated)

60

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

Study Contact Backup

Study Locations

  • France
      • Paris, France, 75015
        • Hôpital Necker-Enfants Malades
        • 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

  • Adult

Accepts Healthy Volunteers

Yes

Sampling Method

Non-Probability Sample

Study Population

Any individual between the ages of 18 and 35, inclusive, with no organic ophthalmological disorders or oculomotor disorders.

Description

Inclusion Criteria:

  • Adults between the ages of 18 and 35 with no known eye conditions, with or without ametropia. If ametropia is present: it must be corrected
  • Subjects with no history of eye surgery, including refractive surgery
  • Subjects who have been informed about the study and have freely and knowingly consented to participate in the study and to the collection of data

Exclusion Criteria:

  • Subjects with strabismus
  • Subjects with visual acuity of less than 20/20; or anisometropia

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

Cohorts and Interventions

Group / Cohort
Intervention / Treatment
Healthy individual
Individuals with no visual or oculomotor disorders.
Other: Fusional Vergence assessment
Measurement of sensorimotor fusional vergence in the right and left eyes, in divergence and convergence, first for distance vision and then for near vision. A random draw will determine which eye is tested first for distance vision, followed by a second draw for near vision, in order to minimize training bias. Prior to this, a stereoscopic acuity test will be performed to confirm the presence of binocular vision.
Other Names:
  • Measurements of sensorimotor fusion
Other: Ocular dominance evaluation

Assessment of ocular dominance for:

  • The dominant eye using the monocular blurriness test and the red-glass test
  • The leading eye using the Mawas plate Punctum Proximum convergence test and the bilateral prismatic test for oculomotor dominance
  • The preferred eye using the spontaneous ocular method
  • The target eye using the Hole-in-Card method: hole-in-card test
Other Names:
  • Assessment of ocular dominance
Other: Complete Orthoptic

Conducting an orthoptic evaluation to verify that patients meet the study's inclusion criteria:

  • assessment of visual acuity and refraction
  • assessment of stereoscopic vision
  • cover-test to screen potential abnormal phorias
  • measurement of interpupillary distance
Other Names:
  • Orthoptic evaluation

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Amplitude of fusional vergence
Time Frame: Day 0
Values of horizontal fusional vergence measured using a horizontal Berens prism bar in divergence and convergence, for distance and near vision, in the right eye and the left eye and reported in prism diopters.
Day 0
Laterality ocular dominance
Time Frame: Day 0

Assessment of ocular dominance for:

  • The dominant eye using the monocular blur test and the red-glass test
  • The leading eye using the Punctum Proximum of Convergence (PPC) test with the Mawas plate and bilateral prism test for oculomotor dominance
  • The preferred eye using the spontaneous ocular method
  • The target eye using the Hole-in-Card method: hole-in-card test All tests classify the ocular dominance into 3 categories : Left, Right, None.
Day 0
Lateralization quotient value (LQ)
Time Frame: Day 0
Determination of the lateralization quotient value by the mean of previous responses of the ocular dominance tests.
Day 0

Secondary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Assessment of the degree of agreement among the various tests for ocular dominance
Time Frame: Day 0
Compilation of responses to ocular dominance tests (sensorial and motor dominant eye, target eye and preferred eye) and lateralization quotient.
Day 0
Agreeement between the bilateral prismatic test (new test for oculomotor dominance laterality determination and standard ocular dominance tests
Time Frame: Day 0
Evaluation of a new test (bilateral prismatic test for oculomotor dominance) and comparison to usually ocular dominance test. All tests classify the ocular dominance into 3 categories : Left, Right, None. This part tends to evaluation the efficacity and the utility of a new test for ocular dominance.
Day 0
Assessment of the difference in fusional vergence measurements between the right and left eyes and the laterality quotient
Time Frame: Day 0
Assessment of the difference in fusional vergence measurements between the right and left eyes and the laterality quotient.
Day 0
Correlation between inter-pupillary distance measurements and differences in fusion amplitude measurements between the right and left eyes
Time Frame: Day 0
Measurements of interpupillary distance and overall fusion ability, for distance vision and near vision.
Day 0

Collaborators and Investigators

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

Sponsor

Assistance Publique - Hôpitaux de Paris

Collaborators

URC-CIC Paris Descartes Necker Cochin

Investigators

  • Principal Investigator: Maxence Rateaux, PhD, Assistance Publique - Hôpitaux de Paris
  • Study Director: Dominique MD, PhD BREMOND-GIGNAC, Assistance Publique - Hôpitaux de Paris

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

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)

September 1, 2026

Primary Completion (Estimated)

July 1, 2027

Study Completion (Estimated)

July 1, 2027

Study Registration Dates

First Submitted

June 22, 2026

First Submitted That Met QC Criteria

July 6, 2026

First Posted (Actual)

July 13, 2026

Study Record Updates

Last Update Posted (Actual)

July 13, 2026

Last Update Submitted That Met QC Criteria

July 6, 2026

Last Verified

June 1, 2026

More Information

Terms related to this study

Keywords

Other Study ID Numbers

  • APHP251987
  • 2025-A02953-46 (Other Identifier: ID RCB number)

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

NO

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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