Related Experiment Video
Updated: Jul 12, 2026
05:14
Comparison of Agreement and Accuracy using Binocular Wavefront Optometer with Autorefractor and Phoropter
Published on: September 16, 2025
The forced vergence cover test and phoria adaptation
1College of Optometry, The Ohio State University, Columbus, OH, USA. atoole@optometry.osu.edu
Summary
Forced vergence cover tests (FVCTs) were evaluated for their ability to overcome phoria adaptation (PA). Neither FVCT-1 nor FVCT-2 effectively revealed the full phoria magnitude, suggesting limited clinical utility for these specific methods.
Area of Science:
- Ophthalmology
- Vision Science
- Neuroscience
Background:
- Phoria adaptation (PA) is an innervation that maintains binocular vergence posture.
- Disrupting fusion, as in phoria measurement, depletes this innervation.
- Extended monocular occlusion is traditionally needed to dissipate PA and reveal full phoria.
Purpose of the Study:
- To evaluate two forced vergence cover tests (FVCT-1 and FVCT-2) for their ability to rapidly dissipate PA.
- To determine if FVCTs can reveal the full magnitude of phoria after adaptation.
Main Methods:
- Phoria adaptation was induced using 15 minutes of base-out prism.
- The standard cover test (CT) followed by FVCT-1 or FVCT-2 was performed before and after prism adaptation.
- Experiments were conducted at 40 cm (FVCT-1, n=13) and 4 m (FVCT-2, n=32).
Main Results:
- Significant PA was confirmed by differences between pre- and post-adaptation CTs (7.8Δ and 5.4Δ).
- FVCT-1 did not show a larger phoria than CT, indicating it did not alter PA.
- FVCT-2 shifted phoria but this shift was constant, independent of PA levels.
Conclusions:
- Neither FVCT-1 nor FVCT-2 demonstrated a dependency on the level of phoria adaptation present.
- These specific forced vergence cover test procedures are unlikely to be effective for revealing the full magnitude of phoria in clinical settings.
