In part 1, I discussed symptoms that occur in a condition for which I have suggested the name “Visually-Based Reading Disability (VBRD).” In part 2, I will describe some of the likely underlying conditions that may cause VBRD and review some of the relevant scientific literature. Let’s review some of the most common symptoms in VBRD:
- Letters/words become blurry or turn double
- Letters/words seem to float all over the page
- The page gets “glary” and hurts eyes
- Loss of place when reading/ re-reading
- There are frequent small word errors (both omissions and substitutions)
- Words move or shimmer on the page
- Can read well when words presented individually, but not when the same words are in a paragraph
Symptoms 1 & 2 are particularly common in”visual input” disorders such as convergence (eye teaming) and accommodative (focusing) disorders. These occur when a person cannot maintain or sustain convergence or accommodation for the time needed to perform near tasks such as reading, studying, take notes, or working on a computer.
Recently, some members of the College of Optometrists in Vision Development
embarked on a Tour de Optometry lecture series to inform current optometry students about the exciting specialty area of developmental optometry. Two of the slides used (below) give a reasonable simulation of what a patient with convergence and accommodative insufficiency experience.
convergence insufficiency simulation:
accommodative insufficiency simulation:
Convergence insufficiency, in particular, has been extensively researched through National Eye Institute funded multi-center clinical trials. It has been found to be a treatable both symptomatically and objectively, most efficaciously with office based vision therapy
Symptoms on the above list #4-7 may be more indicative of a visual processing problem. Specifically, there are two pathways in the brain that are involved in visual processing during reading. The magnocellular (M-cell) and parvocellular (P-cell) pathways. Here is a brief summary of these pathways as they relate to visual processing.
- Mainly involved in peripheral vision and sensitive to motion detection
- Responds to high temporal frequency and low spatial frequency
- Responds to reduced illumination
- Saccades during reading activate this pathway.
- Mainly in central vision and insensitive to motion detection.
- Involved with processing of color information
- More responsive to stationary or slow moving targets
- P-Cells are foveally activated during fixations and extract the details of the text.
Eye movements during reading involve fast eye movements (saccades, M-cell), and pauses to process information (fixations, P-cell). Reading therefore involves the repetitive alternation of saccades and fixations. There is good evidence that the M-cell system is impaired in many poor readers. The role of the visual magnocellular system is probably to mediate steady direction of visual attention and eye fixations on words. Thus many children with reading difficulties have unsteady eye control and this potentially causes the letters they are trying to read to appear to move around (Stein, 2003
). If this is difficult to imagine, then think of the situation of driving in a car between two cities and hearing two radio stations at once. You will most likely either change the station or turn off the radio! This is a good auditory analogy of the type of visual confusion a patient with VBRD probably confronts on a daily basis. They may “turn off the radio” (stop reading) or feel compelled to read slowly and re-read because of the visual confusion VBRD causes.
In part 3 of “The Truth of Visually-Based Reading Disability” , I will discuss diagnostic tests available to us to aid in the diagnosis of VBRD and review our treatment options.