Dyslexia Study Raises Questions About Eye Differences

A new dyslexia study found differences in part of the eye called the fovea. This small region in the back of the eye is packed with red, green and blue light receptors. The study found that the blue light receptors are arranged differently in people who have dyslexia than in people who don’t.

Some news outlets have hailed the findings as a possible “cause” of dyslexia. But experts reject that view for several reasons. One is that the study doesn’t account for what’s already known about dyslexia. For example, it’s well known that trouble with rhyming (something people can do with their eyes closed) is often an early warning sign of dyslexia.

The fovea provides much of the information about vision that the optic nerve takes to the brain. And the anatomical differences observed in this study may play a role in eye dominance. (Most people have a dominant eye just like most people have a dominant hand.)

The researchers also speculate their findings might be related to why some people with dyslexia confuse letters like b and d.

To study the location of the blue light receptors, the researchers used a tool called a foveascope. They examined 60 college students in France. Half of these students had dyslexia and half did not. All had normal vision. (The study noted that the students with dyslexia had been tested by their own optometrists to rule out any eye disorders.)

The findings were published in October in a British peer-reviewed journal called Proceedings of the Royal Society B. Understood experts Guinevere Eden, Sheldon Horowitz and Margie B. Gillis took a look at the study. Here’s the takeaway.

Key Findings

Scientists have known for a long time that the center of the fovea only has red and green light receptors. This kind of light receptor is also called a cone. The new study measured the part of the fovea that doesn’t have any blue cones.

The researchers measured this blue cone-free area in each eye. Then they compared the size and shape of these areas in people who have dyslexia and in people who don’t. The study found:

• In students who don’t have dyslexia, the blue cone-free areas were not the same in each eye. In one eye the area was big and round. In the other eye the area was smaller and narrower.
• The students with dyslexia did not have this asymmetry. Both of their eyes had matching round blue cone-free areas.

The asymmetry of the blue cones may help one eye dominate the other. The dominant eye can “override” conflicting signals from the other eye. This system may help the brain see one coherent image.

And what about the lack of asymmetry in people with dyslexia? The symmetry of the blue cones might mean each eye is sending competing information to the brain. This may result in some people seeing images that are not a true representation of what they’re viewing. In some cases they may see mirror images.

The study suggests these findings may be linked to confusion of mirror-image letters like b and d. But the researchers did not test this directly. More research is needed to see if some blue cone patterns cause more letter reversals when reading text.

It’s also unclear if these differences are a cause or a result of dyslexia.

Key Takeaways for Parents

1. This is one study. It is small and limited to adults. It does not demonstrate that this difference in eye anatomy causes letter reversals or reading difficulties.

A lot would need to happen before scientists could responsibly say this difference is linked to some aspect of dyslexia. The findings would need to be:

• Replicated by other researchers
• Observed in children as well as adults
• Seen in large numbers of people
• Studied over time

“It’s not until we have that kind of research that we know whether the observation is robust,” says Eden. (She is a neuroscientist at Georgetown University.) “We also need that kind of research to know if the finding is a cause rather than just a correlation.”

2. “The core issue with dyslexia isn’t vision,” says Eden. Decades of research point to weak phonological awareness skills as the main reason people with dyslexia struggle to make progress in reading. This consensus is based on:

• Many different labs in different countries finding similar results
• Studies on how phonological awareness skills change over time
• Studies of reading skills before and after phonological instruction

This new study doesn’t address issues with the sound structure of language. “Early signs of dyslexia include trouble with rhyming and other activities that can be done with your eyes closed,” says Gillis. (She is an expert who trains educators on how to use evidence-based reading practices in the classroom.)

3. Letter reversals are common in all beginning readers. Some kids with dyslexia keep confusing mirror-image letters as they get older. Some don’t.

Most students stop making these mistakes as they get more experience as readers and writers. But kids with dyslexia often spend less time reading than their peers because it is such a struggle for them. This kind of task avoidance may result in their taking longer to stop making these mistakes.

Imaging studies also suggest this learning happens where the brain processes visual information. The eye doesn’t change how it takes in information. The brain changes what it does with that information.

4. There is no quick test or quick fix for dyslexia. “A lot of people don’t understand what dyslexia is,” says Gillis. “People want to find a cure, a quick fix.”

“This study is interesting, but it has no practical application for diagnosing dyslexia or treating dyslexia,” says Horowitz. (He is the senior director of learning resources and research at the National Center for Learning Disabilities.) “Any talk of attributing a cause or a cure for dyslexia based on this study is way too premature.”

Learn more about dyslexia and vision. Explore evidence-based treatment for dyslexia. Learn why vision therapy is not recommended for dyslexia. And see an expert explain what dyslexia is and isn’t.

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