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Related Experiment Videos

Vergence adaptation and the clinical AC/A ratio.

M Rosenfield1, J M Rappon, M F Carrel

  • 1SUNY College of Optometry, NY 10010, USA. Rosenfield@sunyopt.edu

Ophthalmic & Physiological Optics : the Journal of the British College of Ophthalmic Opticians (Optometrists)
|July 18, 2000
PubMed
Summary

Slow fusional vergence can affect heterophoria measurements. However, this study found that sustained occlusion did not significantly alter the accommodative convergence to accommodation (AC/A) ratio in participants.

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Area of Science:

  • Ophthalmology
  • Optometry
  • Vision Science

Background:

  • The clinical accuracy of the accommodative convergence to accommodation (AC/A) ratio relies on precise heterophoria measurements.
  • Slow fusional vergence responses can persist for extended periods, potentially biasing heterophoria assessments.
  • Current clinical practice often estimates the AC/A ratio after brief dissociation periods.

Purpose of the Study:

  • To investigate if slow fusional vergence influences the accommodative convergence to accommodation (AC/A) ratio.
  • To compare AC/A ratio measurements before and after a 1-hour period of monocular occlusion.

Main Methods:

  • Participants underwent AC/A ratio measurements.
  • A 1-hour period of continuous monocular occlusion was applied.

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  • AC/A ratios were re-measured immediately after occlusion.

    • Main Results:

    • Near heterophoria significantly changed in 10 of 21 subjects after occlusion.
    • No significant alteration in the AC/A ratio was found in either adapting or non-adapting subgroups.
    • The stimulus AC/A ratio remained largely unaffected by sustained slow fusional vergence.

    Conclusions:

    • While slow fusional vergence impacts heterophoria measurements, it does not significantly alter the stimulus AC/A ratio.
    • Clinical heterophoria assessment may be influenced by sustained vergence adaptation.
    • The AC/A ratio calculation appears robust to short-term vergence adaptation effects.