AC/A - CA/C - or neither? Why we should re-think some theoretical vergence-accommodation models.

Past Event Date: 


Professor Anna Horwood PhD DBO(T), University of Reading, Infant Vision Laboratory, School of Psychology & Clinical Language Sciences, UK


Arvind Chandna

Meeting room: 

Room 204 - Main Conference Room

Event Type: 


Clinicians are taught that the AC/A ratio (accommodation - convergence/accommodation) is an important theoretical concept which should influence patient care. Theoretical teaching on the management of binocular vision problems is often based on this “fixed and stable” relationship – but in practice, it is rarely used to change clinical decision-making, it is rarely measured, and the ratio which IS measured clinically is imprecise.

Scientists investigating vergence-accommodation models are still uncertain about what lies within these models and fail to explain how vergence-accommodation models behave in strabismus and anomalies of binocular vision. 

While the AC/A relationship may be important for a small, select group of patients, the research in our laboratory suggests that, in general, the CA/C (convergence - accommodation/convergence) relationship is much more important in everyday conditions and many clinical situations. 

My talk will outline how issues relating to the CA/C relationship can impact on patient care and our understanding of binocular vision. It will go on to discuss how both the AC/A  and CA/C linkages may be more flexible than generally considered.

Most Recent Publications

Review /discussion pieces

"Disparity-driven vs blur-driven models of accommodation and convergence in binocular vision and intermittent strabismus." Journal of the American Association of Pediatric Ophthalmology and Strabismus, 18 (6). pp. 576-583.

Main methods paper for all subsequent papers:

"The use of cues to convergence and accommodation in naïve, uninstructed participants." Vision Research  , 48(15), 1613-24