Related Experiment Video
Updated: May 25, 2026
08:27
Quantification of Oculomotor Responses and Accommodation Through Instrumentation and Analysis Toolboxes
Published on: March 3, 2023
Evidence that convergence rather than accommodation controls intermittent distance exotropia
Anna M Horwood1, Patricia M Riddell
1Infant Vision Laboratory, School of Psychology & Clinical Language Sciences, University of Reading, Reading RG6 6AL, UK. a.m.horwood@reading.ac.uk
Acta Ophthalmologica
|January 28, 2012
Summary
In distance exotropia, convergence significantly drives accommodation, not the other way around. This explains clinical findings and suggests minus lens therapy corrects overaccommodation from convergence control.
Area of Science:
- Ophthalmology
- Neuroscience
- Vision Science
Background:
- Distance exotropia is a condition affecting eye alignment, particularly during near tasks.
- High accommodative convergence to accommodation (AC/A) ratios are often cited as an explanation for its control.
- The role of convergence accommodation (CA/C) in this condition is less understood.
Purpose of the Study:
- To investigate whether vergence drives accommodation or vice versa in controlling distance exotropia for near fixation.
- To explore the significance of the CA/C relationship in explaining clinical observations of distance exotropia.
Main Methods:
- Nineteen young patients with distance exotropia and 27 controls were studied.
- Simultaneous vergence and accommodation responses were measured using targets with varying visual cues (blur, disparity, looming) at different distances.
- Stimulus and response AC/A and CA/C ratios were calculated for all participants.
Main Results:
- Exotropes exhibited greater accommodation responses and response gains for near targets compared to controls.
- Distance exotropes showed lower response AC/A ratios but significantly higher CA/C ratios in laboratory settings.
- Exotropes primarily utilized binocular disparity, not blur, to perceive target distance.
Conclusions:
- Increased vergence demand in distance exotropia also significantly increases accommodation.
- Minus lens therapy likely functions by rectifying overaccommodation driven by convergence control.
- The CA/C relationship is a key factor in understanding distance exotropia characteristics, including high near stimulus AC/A ratios.
