The Researched Link Between Dyslexia and Vision Issues
Developmental Dyslexia is a reading disorder that emerges in childhood. The primary deficit involves impaired ability to “sound out” words, recognize words, and spell words, which in turn affect reading rate, comprehension, and written expression as well. The disorder of Developmental Dyslexia is most often viewed as stemming from a core linguistic deficit in phonological processing, a premise which has guided the educational interventions thus far.
Until now, there has been a lack of research to compare Dyslexic children’s vision issues with typically developing children. It is validating to see the results of this study, which shows how vision affects reading ability in those identified as Developmentally Dyslexic (DD) and “typically developing” (TD).
To understand what efficient reading requires, it is important to understand the visual skills that must be developed.
In simplest terms, the essential visual skills for reading fluency and information processing are eye TEAMING,TRACKING and FOCUSING. All of these skills require the eyes to work together binocularly.
Eye ‘teaming’ requires the brain to tell the eyes what to do in order to work together efficiently. Eye ‘tracking’ more specifically requires our eyes to fixate (look at the same place), and follow (in smooth pursuit or saccades, jumping from place to place). Deficits in these visual tracking skills is known as an OCULOMOTOR DYSFUNCTION.
Eye ‘focusing’ or ACCOMMODATION requires the lenses inside our eyes to adjust to see clearly at any given distance away. in order to work in tandem as a team while focusing equally well, the eyes must also have VERGENCE skills. When we look at near point, the eyes must CONVERGE (or cross) to the proper degree; conversely, they must DIVERGE (or straighten out) to look at a distance. When a person has trouble with convergence, they may be under converging (Convergence Insufficiency), or over converging (Convergence Excess).The vergence system works synergistically with the accommodation system. When a young person has trouble with accommodation, this is referred to ACCOMMODATIVE DYSFUNCTION which can be an under-focusing ability (Accommodative Insufficiency) or a lack of focusing flexibility (Accommodative Infacility).
Behavioral Optometrists such as Dr. Ted Kadet at Hope Clinic have been making the connection between Dyslexia and vision issues for years
He has been treating patients successfully to alleviate or completely get rid of their symptoms. Even though these issues with teaming, tracking and focusing are fairly common and treatable with Vision Therapy, most of these issues remain undetected and these young people do not always get the help they need. They pass the visual acuity screening test (20/20) and their eye teaming, tracking and focusing remains unchecked as they fall through the cracks in their educational setting. Regarding just one of the issues alone, Convergence Insufficiency (CI), approximately one in ten school-aged children is affected.
The Visagraph used in this study is an infrared eye tracking device that records where the eyes are pointing when engaged in silently reading a short paragraph. The device measures the average number of fixations (eye stops) per 100 words, the average number of regressions (backward eye movements) per 100 words, the average duration of each fixation, the reading rate in words per minute, the directional planing/pattern (left to right, top to bottom), the number of lines read/reread, and the cross correlation between the two eyes (related to binocular coordination). All of these scores are compared to grade level equivalent norms.
Only an eye doctor (Optometrist or Ophthalmologist) has the tools to perform a Functional Vision Evaluation and diagnose binocular instability.
Dr. Ted Kadet of Hope Clinic in Bellevue, Tacoma and Silverdale performs Visagraph testing on readers at our Free Screening, which can be scheduled from our website (www.hopecliniconline.com). The following directory can be helpful in locating other doctors who can perform a Functional Vision Evaluation:College of Optometric Vision Development
As you can see below in this study published by the American Medical Association 2018, there is a marked difference in the visual skills of both of the populations compared. This has far reaching implications in determining the best course of action needed to help those with Dyslexic symptoms.
The top graph shows that the DD population has a much lower reading rate than the TD group when measures by the Visagraph. There are many more fixations in the DD group, meaning that their eyes are picking up tiny chunks of information at a time, only parts of words in many cases, which affects their fluency and the meaning that they derive from what they read. They also have many more regressions (rereading what they have already read), causing their eyes to move forward and backward while they are reading.
The bottom graph shows that the DD population has far greater deficiencies in the areas of Vergence, Accommodation and Oculomotor Tracking.
All of the visual issues that show deficits in the Dyslexia population are treatable by vision therapy.
Our hope is that the results of this important study will be helpful in educating caregivers, doctors and teachers so that those who have been labeled Dyslexic are able to get help with their vision issues. No child labeled Dyslexic should be without the proper functional vision testing that goes well beyond 20/20 vision testing, in order to determine if vision therapy is the recommended course of action. To schedule a Functional Vision Evaluation at Hope Clinic, contact us today and we will be happy to give you the information you need to get you started on the road to recovery.
(Research by: Aparna Raghuram, OD, PhD; Sowjanya Gowrisankaran, PhD; Emily Swanson, BS; David Zurakowski, MS, PhD; David G. Hunter, MD, PhD; Deborah P. Waber, PhD.The ethics committee of Boston Children’s Hospital approved the research protocol.The entire study was conducted according to the principles of the Declaration of Helsinki.)