The Effects of Binocular Vision Impairment on Adaptive Gait. The effects of binocular vision impairment due to monocular refractive blur on adaptive gait involving negotiation of a raised surface. Item Type Thesis Authors Vale, Anna Rights <a rel="license" href="http://creativecommons.org/licenses/ by-nc-nd/3.0/"><img alt="Creative Commons License" style="border-width:0" src="http://i.creativecommons.org/l/by- nc-nd/3.0/88x31.png" /></a><br />The University of Bradford theses are licenced under a <a rel="license" href="http:// creativecommons.org/licenses/by-nc-nd/3.0/">Creative Commons Licence</a>. Download date 27/09/2021 07:47:19 Link to Item http://hdl.handle.net/10454/4931 University of Bradford eThesis This thesis is hosted in Bradford Scholars – The University of Bradford Open Access repository. Visit the repository for full metadata or to contact the repository team © University of Bradford. This work is licenced for reuse under a Creative Commons Licence. Abstract The Effects of Binocular Vision Impairment on Adaptive Gait Keywords: Falls, adaptive gait, stair negotiation, binocular vision, anisometropia, monovision, stereopsis, monocular cues. Impairment of stereoacuity is common in the elderly population and is found to be a risk factor for falls. The purpose of these experiments was to extend knowledge regarding impairment of binocular vision and adaptive gait. Firstly using a 3D motion analysis system to measure how impairment of stereopsis affected adaptive gait during a negotiation of a step, secondly by determining which clinical stereotest was the most reliable for measuring stereoacuity in elderly subjects and finally investigating how manipulating the perceived height of a step in both binocular and monocular conditions affected negotiation of a step. In conditions of impaired stereopsis induced by acutely presented monocular blur, both young and elderly subjects adopted a safety strategy of increasing toe clearance of the step edge, even at low levels of monocular blur (+0.50DS) and the effect was greater when the dominant eye was blurred. The same adaptation was not found for individuals with chronic monocular blur, where vertical toe clearance did not change but variability of toe clearance increased compared to full binocular correction. Findings indicate stereopsis is important for accurately judging the height of a step, and offers support to epidemiological findings that impaired stereoacuity is a risk for falls. Poor agreement was found between clinical stereotests. The Frisby test was found to have the best repeatability. Finally, a visual illusion that caused a step to be perceived as taller led to increased toe elevation. This demonstrates a potential way of increasing toe clearance when stepping up and hence increase safety on stairs. 1 Table of Contents ABSTRACT ................................................................................................................ 1 TABLE OF CONTENTS ............................................................................................ 2 LIST OF TABLES ...................................................................................................... 8 LIST OF FIGURES .................................................................................................... 9 INSERTED MATERIAL ......................................................................................... 12 ACKNOWLEDGEMENTS ...................................................................................... 13 LIST OF PRESENTATIONS AND PAPERS ......................................................... 14 Papers ........................................................................................................................................................ 14 Poster Presentations ................................................................................................................................. 14 Oral Presentations .................................................................................................................................... 14 AIMS AND STRUCTURE OF THESIS .................................................................. 16 Introduction and Aims ............................................................................................................................. 16 Outline of Thesis ....................................................................................................................................... 17 Ethical Approval ...................................................................................................................................... 19 BINOCULAR VISION AND PERCEPTION OF DEPTH ..................................... 20 1.1 Binocular Vision ................................................................................................................................. 20 1.1.1 Visual Field .................................................................................................................................. 20 1.1.2 Corresponding Retinal Points ....................................................................................................... 21 1.1.3 The Horopter ................................................................................................................................ 22 1.1.4 Fusion ........................................................................................................................................... 23 1.1.5 Binocular Summation and Inhibition............................................................................................ 24 1.2 Basis of Depth Perception .................................................................................................................. 26 1.2.1 Monocular Cues ........................................................................................................................... 26 1.2.2 Stereopsis...................................................................................................................................... 27 1.2.3 Random Dot Stereograms ............................................................................................................. 30 1.2.4 Oculomotor Cues .......................................................................................................................... 32 1.2.5 Integration of Depth Cues............................................................................................................. 32 1.3 Neural Basis of Stereopsis .................................................................................................................. 33 1.3.1 Parvocellular and Magnocellular Pathways .................................................................................. 33 1.3.2 Binocular Cells ............................................................................................................................. 34 1.3.3 Processing of Local and Global Stereopsis................................................................................... 35 2 1.4 Ocular Dominance ............................................................................................................................. 36 1.4.1 Definition of Ocular Dominance .................................................................................................. 36 1.4.2 Ocular Prevalence ......................................................................................................................... 38 1.4.3 Neurophysiology of Ocular Dominance ....................................................................................... 39 DISRUPTION TO STEREOPSIS ............................................................................ 41 2.1 Strabismus .......................................................................................................................................... 41 2.2 Amblyopia ........................................................................................................................................... 42 2.2.1 Prevalence and Cause ................................................................................................................... 42 2.2.2 Visual Function in Amblyopia ..................................................................................................... 42 2.3 Impairment of Contrast and Stereopsis ........................................................................................... 43 2.4 Refractive Error ................................................................................................................................. 45 2.5 Monovision .......................................................................................................................................... 47 2.5.1 Definition of Monovision ............................................................................................................. 47 2.5.2 Success of Monovision ................................................................................................................. 48 2.5.3 Ocular Dominance and Monovision ............................................................................................. 49 2.5.4 Visual Performance and Monovision ........................................................................................... 50 2.5.5 Task Performance and Monovision .............................................................................................. 52 2.5.6 Alternative Presbyopic Contact Lens Correction ........................................................................