Characteristics of Visual Function in Asperger’s Syndrome and the Autism Spectrum Amy Whiskens Doctor of Philosophy Aston University April 2010 This copy of the thesis has been supplied on the condition that anyone who consults it is understood to recognise that its copyright rests with its author and that no quotation from the thesis and no information derived from it may be published without proper acknowledgement. 1 Aston University Characteristics of Visual Function in Asperger’s Syndrome and the Autism Spectrum Amy Whiskens Doctor of Philosophy June 2008 Summary Autism is a pervasive developmental disorder and Asperger’s syndrome is part of the spectrum of autism disorders. This thesis aims to: • Review and investigate current theories concerning visual function in individuals with Asperger’s syndrome and high functioning autism spectrum disorder and to translate the findings into clinical practice by developing a specific protocol for the eye examination of individuals of this population. • Investigate whether those with Asperger’s syndrome are more likely to suffer from Meares-Irlen syndrome and/or dyslexia. • Assess the integrity of the M-cell pathway in Asperger’s syndrome using perimetric tests available in optometric practice to investigate and also to describe the nature of any defects. • Evaluate eye movement strategies in Asperger’s whilst viewing both text and images. Also to evaluate the most appropriate methodology for investigating eye movements; namely optical digital eye tracking and electrophysiology methodologies. Findings of the investigations include • Eye examinations for individuals with Asperger’s syndrome should contain the same testing methods as for the general population, with special consideration for clear communication. • There is a depression of M-pathway visual field sensitivity in 57% (8/14) of people with Asperger’s syndrome, supporting previous evidence for an M-cell deficit in some individuals. • There is a raised prevalence of dyslexia in Asperger’s syndrome (26% of a sample of 31) but not necessarily of Meares-Irlen syndrome. • Gaze strategies are abnormal in Asperger’s syndrome, for both reading and viewing of images. With increased saccadic movement and decreased viewing of faces in comparison to background detail. Key words: Asperger’s syndrome, Autism, eye movements, Meares-Irlen syndrome, Magnocellular pathway. 2 To Mum and Rob for helping me believe I could 3 Acknowledgements Firstly I would like to thanks my supervisor Robert Cubbidge for all his input and support over the last three and a half years, particularly for his policing of my terrible grammar in the writing up stages. Also I would like to thank Sarah Hosking for her input and enthusiasm at the start up of this project. Much gratitude goes to Stefano Seri and Andrea Scott for there invaluable help and advice on electrophysiology, without which I would have been lost, and also to all the staff at Aston university for their support. I must also extend a huge thanks to all at Autism West Midlands, Studio 3 and Gheel Autism Services, in particular Linda Woodcock, Andrew McDonnell and Grace Hathaway for their aid support and enthusiasm in the recruitment process. Penultimately I want to send special thanks to the people who have kept my spirits up even on the bad days, for being encouraging and distracting in equal measure, the past and present inhabitants of VS207 Parth Shah, Martin Cardell and Navneet Gupta, Phil Buckhurst and Hetal Patel. A final thanks is to all the volunteers who took part in these projects for their patience and willingness to help, without whom this project could not have happened. 4 Table of contents Thesis Summary………………………………………………………………………2 Acknowledgements ...................................................................................................... 4 Table of contents .......................................................................................................... 5 1.1. History of Autism and The Autism Spectrum............................................ 16 1.2. Definition and Diagnosis............................................................................ 18 1.2.1. Diagnostic and Statistical Manual of Mental Disorders IV (DSM IV)18 1.2.2. International Classification Disease (ICD)- 10 ................................. 20 1.2.3. Other characteristics of Autism.......................................................... 22 1.2.4. Asperger’s Syndrome......................................................................... 23 1.3. Epidemiology ............................................................................................. 24 1.3.1. Figures stated for prevalence by different studies.............................. 25 1.3.2. Age of onset........................................................................................ 27 1.4. Aetiology.................................................................................................... 28 1.4.1. Genetics.............................................................................................. 28 1.4.2. Pregnancy and birth complications .................................................... 29 1.4.3. Environmental factors ........................................................................ 29 1.4.4. Viral.................................................................................................... 30 1.4.5. Diet..................................................................................................... 30 1.4.6. Embryogenesis errors......................................................................... 31 1.4.7. The MMR vaccine.............................................................................. 32 1.5. Physiology.................................................................................................. 34 1.5.1. Brain structure.................................................................................... 34 1.5.2. Imbalance of global/local processing................................................. 38 1.6. Associated conditions................................................................................. 39 1.6.1. Epilepsy.............................................................................................. 39 1.6.2. Attention deficit hyperactive disorder (ADHD)................................. 40 1.6.3. Mental Health problems and ASD ..................................................... 40 1.6.4. Obsessive compulsive disorder (OCD).............................................. 40 1.6.5. Anxiety............................................................................................... 40 1.6.6. Sleep disorder..................................................................................... 41 1.6.7. Depression.......................................................................................... 41 1.6.8. Schizophrenia..................................................................................... 41 1.6.9. Other associated conditions................................................................ 41 5 1.7. Ocular Complications and Associations in ASD ....................................... 43 1.7.1. Ocular refraction................................................................................. 44 1.7.2. Strabismus .......................................................................................... 45 1.7.3. Specific reading disorder/coloured lens use....................................... 46 1.7.4. Oculomotor dysfunction..................................................................... 48 1.7.5. Abnormal looking patterns................................................................. 51 1.7.6. Viewing social scenes ........................................................................ 52 1.7.7. Face perception in autism................................................................... 55 1.7.8. Abnormal gaze strategy and the brain................................................ 58 1.7.9. Abnormal Electroretinogram (ERG).................................................. 61 1.7.10. Motion perception .............................................................................. 61 2. Rationale .............................................................................................................. 63 2.1. Rationale..................................................................................................... 63 2.2. Aims ........................................................................................................... 63 2.3. Location and participants ........................................................................... 64 3. The Eye examination............................................................................................ 67 3.1. Introduction ................................................................................................ 68 3.1.1. ASD and the eye examination............................................................ 68 3.1.2. Refraction and ocular defects in people with intellectual or learning disabilities........................................................................................................... 72 3.1.3. Eye examination in patients with learning disabilities....................... 74 3.1.4. The routine eye examination.............................................................. 78 3.1.5. Measurement of oculomotor balance ................................................. 80 3.1.6. Ocular motility assessment................................................................