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Are Horizontal Fusional Vergences Comparable When Measured Using a Prism Bar and Synoptophore?

Shania Haque1, Sonia Toor2, David Buckley2

  • 1The Eye Centre, Chesterfield Royal Hospital, Chesterfield, UK.

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|March 25, 2024
PubMed
Summary

Horizontal fusional vergences measured by prism bar and synoptophore differ significantly for convergence break points. Wide limits of agreement indicate these methods for measuring vergences should not be used interchangeably.

Keywords:
Fusional vergencesprism barsynoptophore

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Area of Science:

  • Ophthalmology
  • Optometry
  • Vision Science

Background:

  • Horizontal fusional vergences are crucial for maintaining binocular single vision.
  • Accurate measurement of fusional vergences is essential for diagnosing and managing binocular vision disorders.
  • Prism bars and synoptophores are common instruments used to assess these vergence capabilities.

Purpose of the Study:

  • To compare the measurements of horizontal fusional vergences obtained using a prism bar versus a synoptophore.
  • To determine if the two instruments yield comparable results for convergence and divergence amplitudes.

Main Methods:

  • Thirty-two young adults (18-23 years) with normal or corrected-to-normal visual acuity participated.
  • Convergence and divergence blur, break, and recovery points were measured using both a prism bar and a synoptophore.
  • Standardized testing procedures and targets were employed for each instrument.

Main Results:

  • The synoptophore yielded significantly higher convergence break points compared to the prism bar (p=0.001).
  • No significant differences were observed between the two instruments for divergence break points (p=0.32).
  • Both methods demonstrated wide limits of agreement for both convergence and divergence break points.

Conclusions:

  • A statistically and clinically significant difference exists in measuring convergence break points between prism bar and synoptophore.
  • Divergence break point measurements were comparable between the two instruments.
  • Due to significant differences and wide limits of agreement, prism bars and synoptophores should not be used interchangeably for measuring horizontal fusional vergences in clinical practice.