DOCSLIB.ORG

Oculomotor Rehabilitation for Reading Dysfunction in Mild Traumatic Brain Injury

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Oculomotor Rehabilitation for Reading Dysfunction in Mild Traumatic Brain Injury Oculomotor rehabilitation for reading dysfunction in mild traumatic brain injury Item Type Article; Thesis Authors Thiagarajan, Preethi Download date 28/09/2021 16:15:48 Link to Item http://hdl.handle.net/20.500.12648/1144 OCULOMOTOR REHABILITATION FOR READING DYSFUNCTION IN MILD TRAUMATIC BRAIN INJURY Submitted by Preethi Thiagarajan DISSERTATION In partial satisfaction of the requirements for the degree of Doctor of Philosophy in Vision Science State University of New York State College of Optometry © Preethi Thiagarajan 2012 I hereby declare that I am the sole author of this thesis. This is a true copy of the thesis, including any required final revisions, as accepted by my examiners. I understand that my thesis may be made electronically available to the public. ii Abstract Aim Considering the extensive neural network of the oculomotor subsystems, global damage as a result of traumatic brain injury could compromise precise oculomotor control, thus causing reading dysfunction. The aim of the present thesis was to evaluate comprehensively the effect of oculomotor-based vision rehabilitation in symptomatic individuals with respect to nearwork and reading and having a mild traumatic brain injury (mTBI). A wide range of laboratory and clinical parameters related to reading involving vergence, accommodation, and version were tested. Methods Twelve subjects with documented mTBI and nearvision-related symptoms participated in the study. A cross-over, interventional experimental design was used involving true “oculomotor” training and “SHAM” training. Each training protocol was performed for 6 weeks, 2 sessions a week, 45 minutes of actual training per session. During each training session, all three oculomotor subsystems (vergence/accommodation/version) were trained for 15 minutes each in a randomized order. All laboratory and clinical parameters were measured before (baseline) and after true oculomotor (post-OMT) and SHAM (post-SHAM) training. In addition, nearvision- related symptoms were assessed using the Convergence Insufficiency Symptom Survey (CISS) scale. Lastly, subjective attention was measured using the Visual Search and Attention Test (VSAT). iii Results Following true oculomotor training, there was a marked improvement in various laboratory and clinical parameters assessed. Over 80% of the abnormal parameters found at baseline testing were found to significantly improve with training. Dynamics of vergence and accommodation, along with clinically assessed maximum amplitudes, improved markedly. Versional saccadic eye movements demonstrated improved rhythmicity and accuracy. These results together had a significant positive impact on overall reading ability. The improved reading-related oculomotor behavior was reflected in reduction of symptoms. In addition, subjective attention was found to also improve with true oculomotor training. In contrast, none of the aforementioned parameters changed with SHAM training. Conclusions Oculomotor-based vision rehabilitation had a strong positive effect on reading- related oculomotor control. This oculomotor learning effect is suggestive of intact neuroplasticity mechanisms in a compromised brain following TBI. iv Acknowledgements My heartfelt thanks to my advisor Prof. Kenneth J. Ciuffreda for his constant motivation, guidance, and support throughout my graduate program. I am always indebted to him for being my professional father and providing me with an opportunity to learn and acquire scientific knowledge. This project was funded by the US Army, DoD, TATRC. My sincere thanks to them for making this project possible. I thank all my study participants who devoted their precious time for taking part in the study and enlightened me with valuable insights. Thanks to SUNY Graduate program, American Optometric Foundation Ezell Fellowship, Minnie Flaura Turner Memorial Fund, and College of Optometrists in Vision Development for their financial support and encouragement. I would like to thank my Committee members Dr. Jose Manuel Alonso and Dr. Jordan Pola for their comments and suggestions. My sincere gratitude to Dr. William R. Bobier for his helpful comments as an external examiner. Many thanks to Mariano Rodriguez for programming test targets. I acknowledge Diana Ludlam and Naveen Yadav in Ciuffreda’s lab for their help during pilot testing. I would like to thank all the clinicians in the SUNY Head Trauma Clinic for providing me with the subjects. Thanks to Jorge Villon for his technical and computing support. My heartfelt thanks to my friends Anthony Perez, Naveen Yadav, Nili Parekh, Phoram Shah, and Gayathri Thyagarajan for their love, care, and emotional support during my tough times. v Dedication To my parents, brother and aunts for their unflinching love, support and encouragement, To my spiritual Guru for being my lynchpin, & To all TBI survivors vi Table of Contents Abstract ........................................................................................................................................... iii Acknowledgements .......................................................................................................................... v Dedication ....................................................................................................................................... vi Table of Contents ........................................................................................................................... vii Chapter 1 TRAUMATIC BRAIN INJURY – AN OVERVIEW ..................................................... 1 1.1 Definition and classification .................................................................................................. 1 1.2 Mechanisms and Pathophysiology of TBI ............................................................................. 2 1.3 Neuroimaging in TBI ............................................................................................................. 6 Chapter 2 SEQUELAE OF TBI ..................................................................................................... 10 2.1 General sequelae of TBI ...................................................................................................... 10 2.2 Visual sequelae in TBI ......................................................................................................... 12 Chapter 3 THESIS PREAMBLE ................................................................................................... 16 3.1 Introduction .......................................................................................................................... 16 3.1.1 Reading: Basic Concepts .................................................................................................. 16 3.1.2 Investigations on reading in brain injury: Diagnosis .................................................... 17 3.1.3 Oculomotor rehabilitation in TBI ................................................................................. 21 3.1.4 Theory under consideration .......................................................................................... 23 3.1.5 Hypothesis..................................................................................................................... 24 3.2 AIMS OF THE STUDIES ................................................................................................... 25 3.3 METHODS .......................................................................................................................... 29 3.3.1 Subjects ......................................................................................................................... 29 3.3.2 Study design .................................................................................................................. 30 3.3.3 Evaluative Procedures ................................................................................................... 32 3.3.4 Treatment protocol ........................................................................................................ 48 3.4 ANALYSES ......................................................................................................................... 57 3.4.1 Data acquisition and analyses for objective recordings ................................................ 57 3.4.2 STATISTICAL ANALYSES ....................................... Error! Bookmark not defined. 3.5 RESULTS ............................................................................................................................ 60 3.5.1 Laboratory and clinically-based measures of accommodation, vergence, and version 61 3.5.2 Additional subjective tests ............................................................................................ 73 3.5.3 Correlations: Objective and subjective findings ........................................................... 74 vii 3.6 DISCUSSION ...................................................................................................................... 78 3.6.1 True oculomotor training effects ................................................................................... 78 3.6.2 SHAM training effects ................................................................................................ 100 3.6.3 Future directions ......................................................................................................... 101 3.7 CONCLUSIONS...............................................................................................................
Load more

Recommended publications
  • Management of Microtropia
    Br J Ophthalmol: first published as 10.1136/bjo.58.3.281 on 1 March 1974. Downloaded from Brit. J. Ophthal. (I974) 58, 28 I Management of microtropia J. LANG Zirich, Switzerland Microtropia or microstrabismus may be briefly described as a manifest strabismus of less than 50 with harmonious anomalous correspondence. Three forms can be distinguished: primary constant, primary decompensating, and secondary. There are three situations in which the ophthalmologist may be confronted with micro- tropia: (i) Amblyopia without strabismus; (2) Hereditary and familial strabismus; (3) Residual strabismus after surgery. This may be called secondary microtropia, for everyone will admit that in most cases of convergent strabismus perfect parallelism and bifoveal fixation are not achieved even after expert treatment. Microtropia and similar conditions were not mentioned by such well-known early copyright. practitioners as Javal, Worth, Duane, and Bielschowsky. The views of Maddox (i898), that very small angles were extremely rare, and that the natural tendency to fusion was much too strong to allow small angles to exist, appear to be typical. The first to mention small residual angles was Pugh (I936), who wrote: "A patient with monocular squint who has been trained to have equal vision in each eye and full stereoscopic vision with good amplitude of fusion may in 3 months relapse into a slight deviation http://bjo.bmj.com/ in the weaker eye and the vision retrogresses". Similar observations of small residual angles have been made by Swan, Kirschberg, Jampolsky, Gittoes-Davis, Cashell, Lyle, Broadman, and Gortz. There has been much discussion in both the British Orthoptic Journal and the American Orthoptic journal on the cause of this condition and ways of avoiding it.
    [Show full text]
  • Accommodation in the Holmes-Adie Syndrome by G
    J Neurol Neurosurg Psychiatry: first published as 10.1136/jnnp.21.4.290 on 1 November 1958. Downloaded from J. Neurol. Neurosurg. Psychiat., 1958, 21, 290. ACCOMMODATION IN THE HOLMES-ADIE SYNDROME BY G. F. M. RUSSELL From the Neurological Research Unit, the National Hospital, Queen Square, London In 1936, Bramwell suggested that the title response to near and far vision respectively. But it "Holmes-Adie syndrome" be given to the clinical has also been noted that the reaction to convergence complex of a slowly reacting pupil and absent tendon may be remarkably wide in its range, considering reflexes in recognition of the descriptions by Holmes that it often follows a stage of complete paralysis (1931) and Adie (1932). Both authors had empha- (Strasburger, 1902). Not only is the reaction to sized the chief clinical features-dilatation of the convergence well preserved when compared to the pupil, apparent loss of the reaction to light, slow reaction to light, but it may in fact be excessive constriction and relaxation in response to near and (Alajouanine and Morax, 1938; Heersema and distant vision, and partial loss of the tendon reflexes. Moersch, 1939). In assessing the degree of tonicity Although the syndrome had been recognized wholly there are, therefore, two criteria: slowness ofguest. Protected by copyright. or in part many years previously (Strasburger, 1902; pupillary movement and preservation of the range Saenger, 1902; Nonne, 1902; Markus, 1906; Weill of movement. and Reys, 1926), credit must go to Adie for stressing Adler and Scheie (1940) showed that the tonic the benign nature of the disorder and distinguishing pupil constricts after the conjunctival instillation it clearly from neurosyphilis.
    [Show full text]
  • Routine Eye Examination
    CET Continuing education Routine eye examination Part 3 – Binocular assessment In the third part of our series on the eye examination, Andrew Franklin and Bill Harvey look at the assessment and interpretation of binocular status. Module C8290, one general CET point, suitable for optometrists and DOs he assessment of binocular previous question. Leading questions function is often one of the should be avoided, especially when weaker areas of a routine, dealing with children. If they are out if observation of candidates of line ask the patient ‘Which one is out in the professional qualifica- of line with the X?’ Ttions examination is any guide. Tests are You should know before you start the done for no clearly logical reason, often test which line is seen by which eye. because they always have been, and in If you cannot remember it from last an order which defeats the object of the time, simply look at the target through testing. Binocular vision seems to be one the visor yourself (Figure 1). Even if of those areas that practitioners shy away you think you can remember, check from, and students often take an instant anyway, as it is possible for the polarisa- dislike to. Many retests and subsequent tion of the visor not to match that of the remakes of spectacles are the result of a Mallett Unit at distance or near or both, practitioner overlooking the effects of a Figure 1 A distance fixation disparity target especially if the visor is a replacement. change of prescription on the binocular If both eyes can see both bars, nobody status of the patient.
    [Show full text]
  • Università Degli Studi Di Padova Dipartimento Di
    UNIVERSITÀ DEGLI STUDI DI PADOVA DIPARTIMENTO DI FISICA E ASTRONOMIA ˝GALILEO GALILEI˝ CORSO DI LAUREA IN OTTICA E OPTOMETRIA TESI DI LAUREA OPTOMETRIC MANAGEMENT OF VIDEO DISPLAY TERMINAL RELATED VISION PROBLEMS Relatore: Prof. Dominga Ortolan Laureando: Matjaž Turk Matricola: 1124752 Anno Accademico 2018-2019 INDEX 1. INTRODUCTION ............................................................................................. 2 2. NEAR VISION .................................................................................................. 3 2.1 VISUAL SKILLS .......................................................................................... 3 2.2 VERGENCE AND ACCOMMODATIVE DYSFUNCTION ...................... 5 3. COMPUTER VISION SYNDROME .............................................................. 8 3.1 HISTORY OF COMPUTER ......................................................................... 8 3.2 DEFINITION ................................................................................................ 9 3.3 RISK FACTORS FOR CVS ....................................................................... 10 3.4 DIGITAL SCREEN CHARACTERISTICS ............................................... 12 3.5 PATHOPHYSIOLOGY OF CVS ............................................................... 12 4. IMPACT OF DIGITAL DISPLAYS ON VISUAL PERFORMANCE ..... 17 4.1 SYMPTOMS ............................................................................................... 17 4.2 MEASURING COMPUTER VISION SYNDROME ................................ 23
    [Show full text]
  • The Effect of the Fixation Disparity on Photogrammetric Processes
    The Effect of the Fixation Disparity on Photogrammetric Processes SANDOR A. VERES, Asst. Proj., Surveying and Mapping, Purdue University ABSTRACT: This paper reviews the function oj the human eyes in photogram­ metry, and discusses its limitations. The correction of the observation error is presented by mathematical derivations and practical examples. The paper points out the need for continued development of techniques in view of con­ stantly increasing requirements. INTRODUCTION study of coincidence is most important from the photogrammetric point of view. For a HOTOGRAMMETRIC instrumentation has undergone a revolutionary development study of this kind an instrument called a P horopter has been used. since the second World War. A precision photogrammetric instrument today is able to The horopter designed by Tschermak con­ provide measurement to within a precision of sists of thirteen steel channels mounted so as ± 3 microns. By using these precision in­ to converge to the midpoint of the inter­ struments the compensation of errors in­ pupillary base line of the two eyes of an volved in the measurements becomes of pri­ observer. The central channel lies in a median mary importance. The compensation of errors plane, perpendicular to the eyebase of the is based upon the geometrical knowledge of observer, and the others make angles of 1, 2. the source of errors. The human eye is in­ 4, 8, 12, and 16 degrees on each side of the volved in every photogrammetric measure­ central channel. A small vertical steel rod can ment; consequently the geometrical knowl­ slide smoothly in each channel and the rods edge of the errors due to the limi tation of the are mounted for use at visual distances of 20, human eye is very important.
    [Show full text]
  • The Nature, Testing, and Variables Influencing
    THE NATURE, TESTING, AND VARIABLES INFLUENCING FIXATION DISPARITY; ROLE OF THE FUSION LOCK 1 by Leland W. Carr with Dr. James J. Saladin I ... *I Tl.e N.-1• .._1 Tufi"), A.l IJ.,.;.,l/.s I.{l..•• :? F1*'/:·.., /);,,_,. ; ~ R.lc. OF 'Tlc. ~="••1•.. C. •• l( I Introduction A fixation disparity is a small angular measurement of the mis­ alignment of the two eyes which can occur while still permitting single, fused binocular vision. It represents a small error in the aiming of the eyes which occurs without diplopia being detected. Fixation disparity is allowed because of the slight "slippage" pro­ vided to the fusional system through the existence of Panum's fusional areas. So long as binocular alignment is precise enough to place the two retinal images of a single object within corre­ sponding Panum's areas, the final perception is likely to be single and fused. Sensory fusion thus occurs in spite of a small error in motor fusion. A slight muscle imbalance is the rule, rather than the excep­ tion in individuals even with normal assymptomatic binocular systems. It is rare that all twelve extraocular muscles are precisely bal­ anced in their agonist-antagonist relationships, and thus the inate drive to achieve single vision requires a fusional effort to over­ come existing imbalance. When binocularity is dissociated (as with a covertest) the fusional drive is interrupted and the eyes deviate out of alignment under the influence of the muscle imbalance. This deviation under dissociation is referred to as the heterophoria. When both eyes are permitted to view without dissociative conditions the fusional drive to achieve single binocular vision pulls the eyes toward alignment in opposition to the phoric "stress" operating to deviate the alignment.
    [Show full text]
  • Care of the Patient with Accommodative and Vergence Dysfunction
    OPTOMETRIC CLINICAL PRACTICE GUIDELINE Care of the Patient with Accommodative and Vergence Dysfunction OPTOMETRY: THE PRIMARY EYE CARE PROFESSION Doctors of optometry are independent primary health care providers who examine, diagnose, treat, and manage diseases and disorders of the visual system, the eye, and associated structures as well as diagnose related systemic conditions. Optometrists provide more than two-thirds of the primary eye care services in the United States. They are more widely distributed geographically than other eye care providers and are readily accessible for the delivery of eye and vision care services. There are approximately 36,000 full-time-equivalent doctors of optometry currently in practice in the United States. Optometrists practice in more than 6,500 communities across the United States, serving as the sole primary eye care providers in more than 3,500 communities. The mission of the profession of optometry is to fulfill the vision and eye care needs of the public through clinical care, research, and education, all of which enhance the quality of life. OPTOMETRIC CLINICAL PRACTICE GUIDELINE CARE OF THE PATIENT WITH ACCOMMODATIVE AND VERGENCE DYSFUNCTION Reference Guide for Clinicians Prepared by the American Optometric Association Consensus Panel on Care of the Patient with Accommodative and Vergence Dysfunction: Jeffrey S. Cooper, M.S., O.D., Principal Author Carole R. Burns, O.D. Susan A. Cotter, O.D. Kent M. Daum, O.D., Ph.D. John R. Griffin, M.S., O.D. Mitchell M. Scheiman, O.D. Revised by: Jeffrey S. Cooper, M.S., O.D. December 2010 Reviewed by the AOA Clinical Guidelines Coordinating Committee: David A.
    [Show full text]
  • Brock String and the Horopter: a Perspective
    Brock String and the with neurological disorders such as cerebral 2 3 Horopter: A Perspective palsy and traumatic brain injury. A question that has been posed to us on Kenneth J. Ciuffreda, OD, PhD, more than one occasion, frequently with a FAAO, FCOVD-A, FARVO look ranging from inquisitiveness to distain, Diana P. Ludlam, BS, COVT is, “Why the horopter?” Certainly, this is a fair question. Unfortunately, the horopter seems Barry Tannen, OD, FCOVD to be misunderstood by many, and hence Naveen K. Yadav, BS Optom, the question. In our lectures, we have always MS, PhD, FAAO emphasized the concept of the horopter and its clinical importance, with its clinical analog being the all-important “Brock String.”4 Our Over the past number of years, we immediate reply to this question has been, have been involved in the teaching “Why not, as the concept of the horopter is of both normal and abnormal the underpinning for, and basis of, nearly ALL binocular vision at several optometry aspects of normal and abnormal binocular colleges, national and international vision”. This answer usually results in a pause, vision meetings, and vision research sometimes followed by the request for an institutes and hospitals. This has explanation, which we gladly provide in great involved both the underlying detail with numerous clinical examples. theory and its multitude of clinical The horopter is a wonderful pedagogical implications, including the sensory, and clinical tool, as it blends and integrates PERSPECTIVE motor, and perceptual domains and basic aspects
    [Show full text]
  • Ophthalmic Drugs Part 2 — the Pros and Cons of Cycloplegia
    CET Continuing education Ophthalmic drugs Part 2 — The pros and cons of cycloplegia n active ciliary body In the second of our series looking at drugs and their use in controls the eye’s accommodation process, optometric practice, Catherine Viner discusses cycloplegics, how allowing near focusing they work, when they should be used and how to undertake to occur. The ciliary body is made up mainly cycloplegic refraction. Module C19478, one general CET point for Aof smooth muscle, known as the ciliary optometrists and dispensing opticians muscle. Accommodation occurs when the muscarinic receptors within the ciliary muscle are stimulated by the parasympathetic neurotransmitter, acetylcholine (see Part 1 Optician Poor acuity and/or stereopsis 29.06.12). The ciliary muscle then In paediatric patients, these can be contracts, pulling the ciliary body indicative of amblyopia, potentially forward. Tension in the suspensory caused by uncorrected hypermetropia, ligaments supporting the crystalline lens astigmatism, anisometropia or is reduced. As a result, the lens becomes strabismus. To fully investigate the more convex, and thereby increases its cause, a cycloplegic refraction is refractive power. Adequate focus for recommended. nearer targets is then achieved.1 To obtain the true distance correction, Family history of squint, it is imperative that refraction takes amblyopia or hypermetropia place when the patient has relaxed A child is predisposed to these his/her accommodation. For most conditions if a positive family history adults and some children, this can be exists. Should this be the case, due to the achieved by directing the patient to potential risk of amblyopia, it would view a non-accommodative distance seem sensible to fully investigate the target.
    [Show full text]
  • Comparison of a Unique Anaglyphic Vertical Fixation Disparity Test to the Sheedy Disparometer
    Pacific University CommonKnowledge College of Optometry Theses, Dissertations and Capstone Projects 5-2003 Comparison of a unique anaglyphic vertical fixation disparity test to the Sheedy disparometer Paul Stasik Pacific University Randy Kelly Pacific University Matt Hoppe Pacific University Recommended Citation Stasik, Paul; Kelly, Randy; and Hoppe, Matt, "Comparison of a unique anaglyphic vertical fixation disparity test to the Sheedy disparometer" (2003). College of Optometry. 1456. https://commons.pacificu.edu/opt/1456 This Thesis is brought to you for free and open access by the Theses, Dissertations and Capstone Projects at CommonKnowledge. It has been accepted for inclusion in College of Optometry by an authorized administrator of CommonKnowledge. For more information, please contact [email protected]. Comparison of a unique anaglyphic vertical fixation disparity test ot the Sheedy disparometer Abstract The clinical gold standard for deriving vertical prism prescriptions is the patient's vertical associated phoria (The relieving prism to bring a vertical fixation disparity ot zero). It is generally accepted that the most accurate device used to measure fixation disparity at nearpoint is the Sheedy disparometer. However, the Sheedy disparometer is relatively large, expensive and not currently manufactured. These factors may make measurements of vertical associated phorias less appealing and accessible to practitioners. This study evaluated the vertical associated phoria measurements of twenty non- asthenopic subjects with measurable vertical phorias. Vertical associated phoria measurements were made using the Sheedy disparometer and a unique inexpensive anaglyphic vertical fixation disparity test composed of a card with a specifically designed edr and green image and a pair of standard anaglyphic glasses for the patient to wear.
    [Show full text]
  • Causing and Curing Infantile Esotropia in Primates
    Washington University School of Medicine Digital Commons@Becker Open Access Publications 2007 Causing and curing infantile esotropia in primates: The oler of decorrelated binocular input (an American Ophthalmological Society thesis) Lawrence Tychsen Washington University School of Medicine in St. Louis Follow this and additional works at: https://digitalcommons.wustl.edu/open_access_pubs Recommended Citation Tychsen, Lawrence, ,"Causing and curing infantile esotropia in primates: The or le of decorrelated binocular input (an American Ophthalmological Society thesis)." Transactions of the American Ophthalmological Society.105,. 564-593. (2007). https://digitalcommons.wustl.edu/open_access_pubs/3298 This Open Access Publication is brought to you for free and open access by Digital Commons@Becker. It has been accepted for inclusion in Open Access Publications by an authorized administrator of Digital Commons@Becker. For more information, please contact [email protected]. CAUSING AND CURING INFANTILE ESOTROPIA IN PRIMATES: THE ROLE OF DECORRELATED BINOCULAR INPUT (AN AMERICAN OPHTHALMOLOGICAL SOCIETY THESIS) BY Lawrence Tychsen, MD ABSTRACT Purpose: Human infants at greatest risk for esotropia are those who suffer cerebral insults that could decorrelate signals from the 2 eyes during an early critical period of binocular, visuomotor development. The author reared normal infant monkeys, under conditions of binocular decorrelation, to determine if this alone was sufficient to cause esotropia and associated behavioral as well as neuroanatomic deficits. Methods: Binocular decorrelation was imposed using prism-goggles for durations of 3 to 24 weeks (in 6 experimental, 2 control monkeys). Behavioral recordings were obtained, followed by neuroanatomic analysis of ocular dominance columns and binocular, horizontal connections in the striate visual cortex (area V1).
    [Show full text]
  • Binocular Vision
    0331—Foundations of Clinical Ophthalmology—Ch24—R2—05-21-04 15:35:55— advantage in detection of faint images and rejection of the optical distortions within the eyes. 24 4. The presence of two mobile eyes allows the organism to converge the line of sight on distant objects and obtain a reading as to their absolute distance. 5. And, probably the most dramatic reason for binocu- Binocular lar vision, two eyes permit stereoscopic depth per- ception–the ability to use the differences in the im- ages caused by each eye viewing from a slightly Vision different viewpoint, known as binocular disparities, to perceive distance in the third dimension of visual space. Presumably all animals develop a visual system with Christopher W. Tyler some weighting among these different factors. Most lower animals take advantage of the possibility of a 360- degree field of view by having the eyes pointing in op- posite directions. This advantage applies to fish, many birds, and to a large extent, mammals that are preyed upon. However, most predatory animals, from spiders and crustaceans through birds to mammals and humans, Eyes come in pairs, providing special capabilities that tend to have the eyes facing in the same direction. This are not available to a single imaging system. This chap- arrangement is, presumably, to take advantage of stereo- ter provides an overview of the ways that visual process- scopic depth perception, which has been demonstrated ing has evolved to utilize the joint capabilities of a dual in humans, monkeys, cats, and falcons, and is likely to optical system for the perception of the third spatial be widespread across other species.2–5 dimension, of the visual deficits that can occur specific Actually, almost all animals show some degree of to the binocular coupling of this system, and of current binocular overlap, even those with a full 360-degree approaches to ameliorating those deficits.
    [Show full text]