They might not be the first childhood problem parents think about, but reading disorders are almost shockingly prevalent in today’s youth. Roughly five to six percent of all students in the U.S. receive treatment for some form of dyslexia (neurologically-caused reading disorders), and even that high number barely scratches the 20 percent of the population that some experts believe to be dyslexic.
Difficulty reading can severely hurt a child’s performance in school, not to mention their enjoyment of it. Classrooms from elementary school onward are heavily text-based, and an inability to keep up with written material often leads to lower grades.
While these problems can have a wide variety of contributing causes – with dyslexia being among both the most common and most studied – some stem not from neurological or behavioral problems, but from simple shortcomings in eyesight.
Vision-Related Reading Disorders
One of the trickiest things about vision-related disorders is that they come in a confusingly wide selection of mechanisms and magnitudes. As a result, it’s easy for impaired students to slip through vision screenings, which generally only test for visual acuity, and run into later problems in the classroom.
When discussing reading disorders, it’s important to make a distinction between eyesight and vision. Eyesight is a precise term and refers only to visual acuity – if you’ve ever taken a Snellen test (reading off letters of decreasing size from a board), then you’ve had your eyesight tested. Vision is different, and can refer to a wide range of processes that range from physical defects in the eyes to the ways in which they move in response to stimuli.
Convergence falls under the “vision” umbrella. An important part of healthy vision, convergence refers to a person’s ability to remain focused on approaching objects by moving their eyes inward toward one another. If any part of the process doesn’t function properly, performing near-field tasks can become difficult or even painful, resulting in a disorder called convergence insufficiency.
Convergence insufficiency, which affects an estimated five percent of children, is easy to detect if looked for, but can make reading extraordinarily difficult if it’s not. Some screenings do test for convergence insufficiency, but many do not. Even states with truly excellent, broad-spectrum screenings – such as Colorado – only run most tests once during a student’s time with the school, and still rely on nurses, rather than trained eye specialists, to make diagnoses.
If left untreated, convergence insufficiency can cause consistent headaches and dizziness, making day-to-day life difficult, especially in the classroom. Children with the disorder can often look forward to diagnoses for ADHD or other behavioral syndromes, none of which will actually treat the underlying cause of their difficulties.
Other Visual Disorders
Coordination disorders in general are extremely common and result from an individual’s eyes not moving together efficiently or accurately. So-called binocular vision might seem like second nature for adult readers, but it actually doesn’t develop until relatively late in the developmental game. Babies don’t start to use their eyes in concert until around four months of age, with most only reaching “adult” levels of vision by the time they’re one.
By that time, however, many will have coordination disorders. Strabismus, or crossed eyes, is very common. Cases can vary wildly in severity – minor ones cause only minimal inconvenience, but a more serious one can cause many of the same symptoms as convergence insufficiency and may even lead to a lasting visual syndrome known as amblyopia. Also called lazy eye, amblyopia occurs when a child’s brain, dealing with two eyes that don’t see exactly the same thing, begins to prioritize information from one and ignoring the other. If this happens, even an otherwise normal eye won’t fully contribute to vision. Eye exercises and other interventions have shown some promise in curing amblyopia in adults, but for many, the change is permanent.
Exophoria and esophoria are less common, but just as problematic. In the former, eyes will have a slight tendency to turn outwards. In the latter, they’ll have a similar inclination to turn inwards. Both can make focusing occasionally difficult, making reading a frustrating, frequently-interrupted process.
And if we extend our definition of vision to cover neurological processes, even more disorders appear. Peripheral dyslexias are a class of reading disorders characterized by their affects on the visual system. They include pure dyslexia, also called word blindness, and hemianopic dyslexia, in which a reader’s visual field has decayed due to brain damage.
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Treating Reading Disorders
The good news: once the cause of a reading disorder is understood, treatment usually follows. The term usually used is vision therapy, and can call for corrective lenses, special assisting devices, or the use of drills and exercises that help sharpen deficient visual skills.
For convergence insufficiency, for example, therapists often make use of several different eye exercise drills. The Brock String, a length of white string with several differently colored beads strung onto it, helps patients practice converging by switching their focus from one bead to the next.
Vectograms, on the other hand, consist of two polarized images placed next to one another. Using special lenses, patients can be made to see each side with only one eye. The test is useful in detecting disparities between the eyes, something particularly important for treating people with strabismus or developing amblyopia.