healthHealth and Medicine

Scientists May Have Found Out What Causes Dyslexia


Robin Andrews

Science & Policy Writer


Dyslexia affects nearly 3/4 of a billion people worldwide. Chloe Langton/Shutterstock

Dyslexia, a learning difficulty that affects reading, writing, and spelling skills, is more widespread than you probably think. As much as 5-10 percent of the global population has it – and despite its commonality, its causes remain poorly understood.

A remarkable new piece of research has now concluded that strange patterns of light receptors in the eyes may be the primary cause of the condition.


Writing in the Proceedings of the Royal Society B, a team at the University of Rennes found that the cells responsible for absorbing incoming light within the eyes are arranged differently in people diagnosed with dyslexia.

In this case, we’re talking about the cone cells – those that deal with red, blue, and green color light. In people without dyslexia, these cells are in asymmetric layouts; one eye features one pattern, and the other features a different arrangement.

This allows complex, multi-angle light sources to be absorbed differently through each eye. After “weighing up” which is likely to be more accurate, the brain then chooses the image from one eye – and in the long term, this leads to the development of a “dominant” eye that the brain relies on more heavily.

Dyslexic people appear to have symmetric arrangements, though, with both eyes containing the exact same layout of cone cells. This leads to identical absorption patterns, which the brain sees as “mirror” images.


This lack of a dominant eye explains why dyslexic people see“3” and “E” as being the same. Their brains cannot properly distinguish between mirrored shapes that well.

This asymmetry can be seen with unbelievable precision. At the center of the retina – the fovea – there's a small spot that contains no blue cone cells. In non-dyslexic people, this spot is round in the dominant eye, and somewhat warped in the other eye. In dyslexic people, both eyes have the exact same round spot.

It’s not yet clear why these symmetric cellular layouts only emerge in certain people. Although dyslexia is unrelated to a person’s general intelligence, it does appear to run in families, so it’s been thought that genes play a role.

In any case, the identification of this possible physiological cause of dyslexia is nothing but good news. After all, if you know what the problem actually is, you can start to find a way to fix it, if, of course, you see it as a problem in the first place. People with dyslexia sometimes see it as not something that needs to be "fixed," but a type of creative advantage.


The team found that invisible flashing lights from an LED lamp negates one of the “mirror” images in the brain, allowing it to see each letter in its true form. Although not a long-term fix for dyslexia, this marks the start of a whole new range of treatments that could improve hundreds of millions of people’s learning capabilities across the world.

The researchers are well aware of the potentially dramatic implications of their work. "The interplay between the lack of asymmetry and the development in the neural maturation of the brain pathways suggests new implications in both fundamental and biomedical sciences," their study concludes.

It's worth pointing out that this is just one study, and that plenty of other researchers view dyslexia as a neurological trait. Perhaps these visual differences are a consequence, rather than a trigger, of dyslexia.

At the very least, this new study will reinvigorate the scientific debate around the subject.


[H/T: AFP]


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