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The accommodative-convergence complex — A review
Published in Jan-Tjeerd de Faber, 28th European Strabismological Association Meeting, 2020
R.L. Brautaset, J.A.M. Jennings
Vergence eye movements (the common term for either convergence or divergence) are prerequisites of normal binocular vision. Vergence movements minimize retinal disparity and place the two retinal images of a single object on corresponding retinal points. Analogous to accommodation, vergence movements have been identified as containing the following four features (Maddox, 1886): (1) Fusional vergence, the part of the vergence movement necessary to achieve sensory fusion and avoid diplopia and which occurs in response to retinal disparity. Retinal disparity provides information about both direction and magnitude for the fusional vergence movement needed. (2) Tonic vergence, a continuous effort of convergence, which maintains the eyes in their physiological position of rest. (3) Proximal vergence, the part of the vergence movement initiated by an awareness of a near object. (4) Accommodative vergence (AC), the part of the vergence reflex that occurs solely due to changes in accommodation. If one eye is occluded so that there is no stimulus for vergence movements, and the other eye is presented with an accommodative stimulus, then the occluded eye will make a vergence movement. The process of removing vergence stimuli is referred to as making the vergence system “open-loop”.
Rehabilitation and management of visual dysfunction following traumatic brain injury
Published in Mark J. Ashley, David A. Hovda, Traumatic Brain Injury, 2017
Vision therapy for poorly compensated exophoria or convergence insufficiency should include fusional exercises to improve the amplitude of and the ability to sustain convergence as well as the speed of reflex fusion. Convex lenses may be used to work fusional convergence through the accommodative–convergence loop. Viewing through the convex lens relaxes accommodative–convergence so that the patient must exert more fusional convergence to avoid diplopia. Prisms can be used for manipulating images, causing the fusional vergence system to respond to the displaced image. Polarized or anaglyphic materials may be used in order to create second- or third-degree fusion targets (i.e., flat fusion or stereoscopic fusion, respectively), which can be manipulated to expand vergence ranges. At the same time, matches are developed between the ocular–motor feedback and position-in-space interpretation. Many specialized instruments have been developed for treatment of such binocular disorders. Some of these techniques may be prescribed for application by occupational therapists. Many of these techniques require more experience in vision therapy or more extensive instrumentation for effective application and, therefore, need to be performed in the vision care setting.
Prevalence of binocular vision dysfunctions in professional football players
Published in Clinical and Experimental Optometry, 2022
Jorge Jorge, Alberto Diaz-Rey, Madalena Lira
Porcar et al.29 presented the results of a study on symptomatic accommodative and non-strabismic binocular dysfunctions in adult video display unit users. These authors concluded that 22.5% of the participants had binocular vision dysfunctions, with convergence excess as the most frequent, followed by fusional vergence dysfunction. The study of Porcar et al.29 was one of the first to mention esophoria as the main cause for binocular vision dysfunctions, while the decrease of fusional vergences was noted as the second cause. Although these results were obtained for a population with a high near vision demand, they are in line with the results of the present study. One can speculate that the way athletes occupy their free time, such as using the smartphone or playing video games, may lead to the emergence of visual dysfunctions that are characteristic of other populations.20,30
Combined passive and active treatment in strabismic amblyopia with accommodative component
Published in Clinical and Experimental Optometry, 2020
Ainhoa Molina‐martín, Santiago Martín‐gonzález, Igor Illarramendi‐mendicute, Juan A Portela‐camino
The following study presents an intervention protocol that facilitates the restoration of binocular vision through prismatic correction and posterior fusional vergence therapy. With small‐angle strabismus, the prismatic correction was able to be removed with fusional vergence therapy alone. However, where larger angles (> 12Δ) were involved, strabismus surgery was necessary before the prisms could be removed. The sample size did not allow the comparison between the therapy and the surgical group; notwithstanding, all subjects in the surgical group achieved good outcomes in terms of residual angle (orthotropia) and fine stereoacuity. These good surgical results could be explained by the fact that the surgical angle of deviation was calculated according to a stable deviation angle, and this was possible thanks to the previous prismatic correction and visual therapy treatment. Prismatic correction was able to facilitate accurate calculation of the deviation before surgery. Fusional vergence therapy was able to provide subjects a range of fusion around this angle. The PEDIG analysed the stability of subjects with partially accommodative esotropia in a longitudinal study,33 finding that only 39 per cent of the sample had a stable deviation (that is, a variation ≤ 5Δ between measures). Birch et al.34 concluded that subjects with accommodative esotropia and null stereopsis present greater instability in their angle of deviation, hence the acquisition of stereoacuity may stabilise the angle after surgery.
Binocular Function in Subjects with Orthotropic Duane Retraction Syndrome
Published in Journal of Binocular Vision and Ocular Motility, 2019
Bhagya Lakshmi Marella, Ruby Moharana, Ramesh Kekunnaya
To the best of our knowledge, this is the first study to investigate binocular functions in subjects with orthotropic DRS. There were some limitations to the study. First, we could not recruit Type 2 DRS due to the rarity of the condition. Second, some subjects had large exophoria which could be one of the factors affecting the fusional vergence especially for near. Further, we could not administer CISS questionnaire to know about the symptoms of CI in DRS subjects. Future studies are required to look into the changes in binocular vision parameters with and without AHP as we have excluded the subjects with AHP and also take motility restriction into consideration for the analysis and see the correlation between all types.