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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
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.
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.
- 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.