13th Bielschowsky Lecture: Accommodation and Convergence – Ratios, Linkages, Styles and Mental Somersaults

I was very honoured to be awarded this prestigious lecture, given in 2018. The full version appears in JAAPOS  2019 pp 10-19. https://doi.org/10.1016/j.jaapos.2018.07.004 

Email me for a copy if you do not have access to the Transactions

Purpose/Relevance
Understanding the linkages between accommodation and convergence is fundamental to understanding concomitant strabismus, heterophoria and convergence and accommodation anomalies. The lecture will present an alternative conceptual framework around these two systems which fits clinical characteristics and responses to treatment as well, or better than, current models. The framework is based on the different weights the visual system places on the main cues to target position in depth across development and between patient groups.

Target audience
Strabismologists, developmentalists, and all healthcare professionals managing patients with concomitant strabismus.

Current practice
Accommodative convergence has traditionally been considered the major driver to the motor responses involved in near fixation; existing in a fixed, inflexible relationship expressed as the AC/A ratio. This viewpoint, however, only fits a small number of clinical diagnoses and fails to explain many others.

Best practice
Our research suggests that the majority of non-strabismic people, and patients with intermittent strabismus, use binocular disparity as their primary visual cue, with blur and proximal/looming cues having less weight. The convergence to accommodation (CA/C) linkage is therefore more important than the AC/A relationship. Between-diagnosis differences in the relative balance between AC/A and CA/C relationships can explain many clinical findings.

Expected outcomes
Increased awareness of accommodation / convergence linkages, their strengths, their development and variability, which can be used to explain clinical findings and predict responses to common treatments.

Instead of thinking “accommodation drives convergence,” or even “convergence drives accommodation, we should instead think of the visual and non-visual cues which drive both.