Reduced vergence adaptation is associated with a prolonged output of convergence accommodation in convergence insufficiency

Sreenivasan, Vidhyapriya; Bobier, William R.

doi:10.1016/j.visres.2014.04.003

Cited by 19 publications

(26 citation statements)

References 37 publications

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“…Previous work has demonstrated that changes in accommodative‐convergence from prolonged blur‐driven accommodation produced only small reductions (less than 1 ° ) in the measurements of tonic vergence (North et al ., ). Our laboratory has recently reported that tonic accommodation, measured while monocularly viewing a Difference of Gaussian target, was not altered after prolonged convergence was stimulated using an optical prism at 40 cm (Sreenivasan & Bobier, ). Furthermore, another group employed a similar dichoptic design and non‐congruent convergence disparities as ours to adapt TV and reported no change in tonic accommodation when measured in a dark, empty field (Satgunam et al ., ).…”

Section: Discussionmentioning

confidence: 99%

“…Convergence insufficiency (CI) results in poor convergence responses to step changes in target depth and is estimated to exist in up to 12% of the general population and roughly 50% of patients suffering from a traumatic brain injury (Cooper & Jamal, ). Research has shown that patients with CI possess weak FV and SV responses (Daftari et al ., ; Sreenivasan & Bobier, ). Our data support the models that indirectly suggests CI is a malfunction in the generation of the fast corrective movement in response to disparity (Schor, ; Maxwell et al ., ).…”

Section: Discussionmentioning

confidence: 99%

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Unmasking the linear behaviour of slow motor adaptation to prolonged convergence

Erkelens

Thompson

Bobier

2016

Eur J of Neuroscience

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Adaptation to changing environmental demands is central to maintaining optimal motor system function. Current theories suggest that adaptation in both the skeletal--motor and oculomotor systems involves a combination of fast (reflexive) and slow (recalibration) mechanisms. Here we used the oculomotor vergence system as a model to investigate the mechanisms underlying slow motor adaptation. Unlike reaching with the upper limbs, vergence is less susceptible to changes in cognitive strategy that can affect the behaviour of motor adaptation. We tested the hypothesis that mechanisms of slow motor adaptation reflect early neural processing by assessing the linearity of adaptive responses over a large range of stimuli. Using varied disparity stimuli in conflict with accommodation, the slow adaptation of tonic vergence was found to exhibit a linear response whereby the rate and amplitude of the adaptive effects increased proportionally with stimulus amplitude. These results suggest that this slow adaptive mechanism represents an early neural process, implying it is a fundamental physiological process that is potentially dominated by subcortical and cerebellar substrates.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Unmasking the linear behaviour of slow motor adaptation to prolonged convergence

Erkelens

Thompson

Bobier

2016

Eur J of Neuroscience

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“…Poor vergence adaptation13, 18, 19 reduced ability of the system to make rapid changes to the decay of the convergence accommodation (CA) amplitudes,18, 19 unstable monocular preference 23 and asymmetry in eye movements, and convergence peak velocity 24 have been reported to be associated with CI. Vision therapy or orthoptic training program has been shown to improve the vergence adaptation, improve the decay of the convergence accommodation output, and eye movement parameters in CI 15, 19, 24.…”

Section: Discussionmentioning

confidence: 99%

“…It is hypothesized that conventional orthoptic therapy such as pencil push-up exercises alone may not improve the vergence adaptation as the stimulus to both accommodation and vergence are congruent in such training 18, 19. A structured in-office VT program where the therapy is designed in a way that the accommodation and vergence systems are incongruent may improve vergence adaptation and clinical vergence parameters 8, 9, 19.…”

Section: Discussionmentioning

confidence: 99%

“…Literature reporting near phoria changes with vision therapy is equivocal 14, 15, 16, 17. Recent studies have reported that vergence adaptation and concurrent decay of convergence output could be improved with a standard VT protocol 18, 19. If poor vergence adaptation is the underlying mechanism in CI, it would be logical to predict that the change in vergence adaptation would alter the cross link ratios of accommodative convergence to accommodation (AC/A) and convergence accommodation to convergence (CA/C).…”

Section: Introductionmentioning

confidence: 99%

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Changes in stimulus and response AC/A ratio with vision therapy in Convergence Insufficiency

Singh¹,

Mani

Hussaindeen

2017

Journal of Optometry

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PurposeTo evaluate the changes in the stimulus and response Accommodative Convergence to Accommodation (AC/A) ratio following vision therapy (VT) in Convergence Insufficiency (CI).MethodsStimulus and response AC/A ratio were measured on twenty five CI participants, pre and post 10 sessions of VT. Stimulus AC/A ratio was measured using the gradient method and response AC/A ratio was calculated using modified Thorington technique with accommodative responses measured using WAM-5500 open-field autorefractor. The gradient stimulus and response AC/A cross-link ratios were compared with thirty age matched controls.ResultsMean age of the CI and control participants were 23.3 ± 5.2 years and 22.7 ± 4.2 years, respectively. The mean stimulus and response AC/A ratio for CI pre therapy was 2.2 ± 0.72 and 6.3 ± 2.0 PD/D that changed to 4.2 ± 0.9 and 8.28 ± 3.31 PD/D respectively post vision therapy and these changes were statistically significant (paired t-test; p < 0.001). The mean stimulus and response AC/A ratio for controls was 3.1 ± 0.81 and 8.95 ± 2.5 PD/D respectively.ConclusionsStimulus and response AC/A ratio increased following VT, accompanied by clinically significant changes in vergence and accommodation parameters in subjects with convergence insufficiency. This represents the plasticity of the AC/A crosslink ratios that could be achieved with vision therapy in CI.

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A differential role for the posterior cerebellum in the adaptive control of convergence eye movements

et al. 2020

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Introduction: The vergence oculomotor system possesses two robust adaptive mechanisms; a fast "dynamic" and a slow "tonic" system that are both vital for single, clear and comfortable binocular vision. The neural substrates underlying these vergence adaptive mechanisms in humans is unclear. Methods: We investigated the role of the posterior cerebellum in convergence adaptation using inhibitory continuous theta-burst repetitive transcranial magnetic stimulation (cTBS) within a double-blind, sham controlled design while eye movements were recorded at 250hz via infrared oculography. Results: In a preliminary experiment we validated our stimulation protocols by reproducing results from previous work on saccadic adaptation during the classic double-step adaptive shortening paradigm. Following this, across a series of three separate experiments we observed a clear dissociation in the effect of cTBS on convergence adaptation. Dynamic adaptation was substantially reduced while tonic adaptation was unaffected. Baseline dynamic fusional vergence response were also unaffected by stimulation. Conclusions: These results indicate a differential role for the posterior cerebellum in the adaptive control of convergence eye movements and provide initial evidence that repetitive transcranial magnetic stimulation is a viable tool to investigate the neurophysiology of vergence control. The results are discussed in the context of the current models of implicit motor adaptation of vergence and their application to clinical populations and technology design in virtual and augmented head mounted display architectures. Significance statement: The cerebellum plays a critical role in the adaptive control of motor systems. Vergence eye movements shift our gaze in depth allowing us to see in 3D and exhibit two distinct adaptive mechanisms that are engaged under a range of conditions including reading, wearing headmounted displays and using a new spectacle prescription. It is unclear what role the cerebellum plays in these adaptive mechanisms. To answer this, we temporarily disrupted the function of the posterior cerebellum using non-invasive brain stimulation and report impairment of only one adaptive mechanism, providing evidence for neural compartmentalization. The results have implications for vergence control models and applications to comfort and experience studies in head-mounted displays and the rehabilitation of clinical populations exhibiting vergence dysfunctions.

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Reduced vergence adaptation is associated with a prolonged output of convergence accommodation in convergence insufficiency

Cited by 19 publications

References 37 publications

Unmasking the linear behaviour of slow motor adaptation to prolonged convergence

Unmasking the linear behaviour of slow motor adaptation to prolonged convergence

Changes in stimulus and response AC/A ratio with vision therapy in Convergence Insufficiency

A differential role for the posterior cerebellum in the adaptive control of convergence eye movements

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