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NCT Number: NCT07697131

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

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.

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Key information

Conditions

No Eye Disorder

Age range

18 year–35 year

Sex eligibility

All sexes

Study type

Observational

Primary location

About this study

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.

Who can participate

Healthy volunteers accepted: Yes

Only the study team can determine whether someone qualifies for participation.

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

Treatment and study plan

Fusional Vergence assessment

Other

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

Ocular dominance evaluation

Other

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

Complete Orthoptic

Other

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

Primary outcomes

  1. 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.

  2. 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.

  3. 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.

Secondary outcomes

  1. 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.

  2. 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.

  3. 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.

  4. 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.

Study contacts

Contact information is provided by the study sponsor or research team.

Hélène Morel

CONTACT

[email protected]

01 44 38 16 53 ext. +33

Maxence Rateaux, PhD

CONTACT

[email protected]

01 44 49 53 62 ext. +33

Sponsors and collaborators

Lead sponsor

Assistance Publique - Hôpitaux de Paris

Other

Collaborators

  • URC-CIC Paris Descartes Necker Cochin

Registry information

Acronym: ECAFOSS

Important dates

Study start
2026
Primary completion
2027
Study completion
2027
First posted
Jul 13, 2026
Registry last updated
Jul 13, 2026

OpenTrials presents study information sourced from ClinicalTrials.gov. The official registry record should be consulted for the latest information.

View the official ClinicalTrials.gov record (opens in a new tab)

This listing is for discovery and informational purposes only. It is not medical advice, does not guarantee that a study is recruiting, and does not determine eligibility. Contact the study team and a qualified healthcare professional when considering participation.

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