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Bielschowsky Lecture

13th Bielschowsky Lecture

Accommodation and Convergence
-Ratios, Linkages, Styles, and Mental Somersaults

Anna Horwood, PhD, DBOT

Professor of Orthoptics and Visual Development
University of Reading, UK


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.


Keynote lecture


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.



  1. Horwood A, Riddell P. Can misalignments in typical infants be used as a model for infantile esotropia? Invest Ophthalmol Vis Sci. 2004;45(2):714-20.
  2. Horwood A, Riddell P. The use of cues to convergence and accommodation in naïve, uninstructed participants. Vision Research. 2008;48(15):1613-24.
  3. Horwood A, Riddell P. Hypo-accommodation responses in hypermetropic infants and children. BJOphth 2011;95( 2):231-7.
  4. Horwood A, Riddell P. Evidence that convergence rather than accommodation controls intermittent distance exotropia. Acta Ophthalmol Scand. 2012
  5. Horwood A, Riddell P. Developmental changes in the balance of disparity, blur and looming/proximity cues to drive ocular alignment and focus. Perception. 2013;42:693-715.


11:25–11:30 AM
Introduction of Bielschowsky Lecturer – Stephen P. Kraft, MD

11:30–11:55 AM
The 13th Bielschowsky Lecture-  Anna Horwood, PhD, DBOT

Alfred Bielschowsky Lecture

Alfred Bielschowsky, MD (1871–1940)
The Bielschowsky Lecture is the named lecture of the International Strabismological Association. The Lecture honors Dr. Alfred Bielschowsky, the prominent German university ophthalmologist who emigrated to the United States in 1936 to become the head of the Dartmouth Eye Institute in Hanover, New Hampshire. In his four short years in the United States before his death in 1940, Alfred Bielschowsky established a heritage of scientific observation, discovery, and exposition that became a critical catalyst for future advances.

Past Bielschowsky Lecturers

1970 Gunter K. von Noorden Acapulco

1974 Heinrich Harms Italy

1978 Arthur Jampolsky Kyoto

1982 Kenneth Wybar Asilomar

1986 Bruno Bagolini Rome

1990 Peter O. Bishop Gold Coast

1994 Alberto O. Ciancia Vancouver

1998 Eugene M. Helveston Maastricht

2002 Emilio C. Campos Sydney

2006 David L. Guyton São Paulo

2010 Burton J. Kushner Istanbul

2014 Tsuranu Yokoyama Kyoto

March 19 @ 11:25


– 11:55


International Ballroom Center

Anna Horwood, PhD, DBOT

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