Vergence Adaptation & Vision Rehabilitation

What are Vergence Eye Movements?

Vergence eye movements allow us to change our depth of focus and see in 3D. The ability to recalibrate these eye movements is crucial for accurate depth perception in different visual environments, just as adaptation is crucial in many other aspects of our success and survival. With virtual and augmented reality technology becoming increasingly popular, understanding the adaptive capacities of vergence eye movements has never been more important.

Disruption of the neural pathways that control vergence plasticity is common in eye movement disorders such as convergence insufficiency (CI). CI is a clinical condition that impairs our ability to quickly and accurately converge our eyes to focus up close. These disorders exist in 5-10% of school age children and up to 50% of patients suffering a traumatic brain injury (TBI) (Cooper, 2012). Problems with vergence eye movements and binocular vision can severely impact reading skills and academic achievement, often resulting in the misdiagnosis of a learning disability. Common symptoms of convergence insufficiency include blurry or double vision, headaches, eye strain, and tiredness while focusing up close. Rehabilitating the neurological systems controlling vergence eye movements can improve the quality of life for individuals suffering from traumatic brain injury (TBI) and vergence eye movement disorders. By understanding the neurological origins and mechanisms of vergence adaptation, we can better develop vision training therapies which are currently the best means for treatment of vergence dysfunctions (Cooper, 2012).

How I was involved as a Student

 Applying cTBS over the cerebellum of a participant. - Submitted by Author

 Applying cTBS over the cerebellum of a participant. - Submitted by Author

This summer as a research assistant, I was involved in projects at the Bobier Lab at the University of Waterloo, School of Optometry and Vision Science, examining the involvement of the cerebellum in vergence control and adaptation. As an undergraduate student interested in a career in optometry this was an incredible opportunity for me! I was completely immersed in optometric and neuroscientific research for the summer which allowed me to explore both fields in-depth. I gained significant exposure to research and clinical techniques, allowing me to develop a comprehensive understanding of optometry in many areas I was unfamiliar with before the beginning of my co-op term. It was extremely rewarding when I began to soak up what I was learning and begin using the optometric language around me. I really enjoyed being in an environment with so much focus on learning and growth. Anyone considering a career in research or a professional school has a lot to gain from involvement in research. Following this experience, I found myself more confident in challenging my abilities, because I grew so much during the summer.

The project I worked on employed a combination of non-invasive brain stimulation, psychophysics and high-speed eye tracking to investigate the role the cerebellum plays in vergence plasticity. I was responsible for running participant visits, which included applying brain stimulation and recording eye movements, as well as participant recruitment and screening. As such, I learned several optometric tests, was trained in proper brain stimulation and eyetracking procedures, and developed optimal standard operating procedures for all participant visits. I also analyzed data via Microsoft Excel, Matlab, and GraphPad software which I learned to use over the course of my co-op.

The results of this work suggest the cerebellum plays a substantial role in fine-tuning and adapting movements based on feedback from other areas of the brain after the visual system is stimulated. Adaptation was significantly impaired following active (non-placebo) stimulation. The size, speed, and duration of the vergence movements all indicated slower, less accurate adaptation. However, stimulation did not significantly impact the basic control of vergence, suggesting that a separate mechanism may regulate basic control. The next step in this research is to attempt to increase adaptation and train the neural pathways involved while they are more plastic. This is a new and exciting avenue for working towards better rehabilitation of the adaptive capabilities of TBI patients and persons with vergence disorders.

The research that I performed was based off of previous research done by Patterson et al. and Calderon et al, if you’re interested in this research you should read more or contact me at



Alicia MacMillan

Alicia is a Guest Author at the ASRJ, she is a biochemistry student at the University of New Brunswick, Fredericton. She developed an interest in research through her participation in Canada-Wide Science Fair, and has since used her research experiences to gain a deeper understanding of the fields she is passionate about. Her main concentration is on optometry, in which she plans to pursue a career, possibly with focus on pediatrics or sports vision. In her spare time, Alicia enjoys waterskiing, figure skating, and reading.


1. Cooper J, Jamal N. Convergence insufficiency-a major review. Optometry. 2012;83(4):137-158.

2. Calderon CM, Erkelens I, Patterson H, Bobier W, Thompson B. Modulation of oculomotor control & adaptation with cerebellar TMS: effects on saccades. Journal of Vision. 2017;17(10):737-737. doi:10.1167/17.10.737.

3. Patterson H, Erkelens I, Calderon CM, Bobier W, Thompson B. Modulation of oculomotor control & adaptation with cerebellar TMS: effects on slow-tonic vergence adaptation. Journal of Vision. 2017;17(10):161-161. doi:10.1167/17.10.161.


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