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

Condition(s) studied

Investigational drug(s) / intervention(s)

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.

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

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

Study summary

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.

Eligibility

Primary outcome measure(s)

• Amplitude of fusional vergence — 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.
• Laterality ocular dominance — 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.
• Lateralization quotient value (LQ) — Day 0
  Determination of the lateralization quotient value by the mean of previous responses of the ocular dominance tests.

Trial sites (1)

More Assistance Publique - Hôpitaux de Paris trials in France