Definitions of health conditions matter, because they inform diagnosis, support, treatment, and future research.
Dyslexia has just got its first official definition update in more than two decades, and it's a major one.
Dyslexia is a condition that affects information processing in the brain: People with it may have problems remembering and working through what's presented to them, and that can show up in difficulties with reading, writing, and pronunciation.
The updated definition, published in the Annals of Dyslexia and authored by researchers from the US, is the result of a consultation with more than 15 international experts on the condition, and reflects recent progress in our knowledge of what dyslexia is.
One of the biggest changes here is the removal of IQ tests for dyslexia. Previously, for someone to be diagnosed as dyslexic, there needed to be a 15-point gap between their reading test score and their score on a standardized IQ test – essentially showing their reading was unusually poor given their overall intelligence.
"There were many children that came close to that definition, but just missed that 15-point difference by one point," says educational psychologist R. Malatesha Joshi, from Texas A&M University.
"Because of that, they were not allowed further help.
"We have taken out the brain-based content so people don't think there is something wrong with their brain if they cannot read or have dyslexia."
Previously, someone with dyslexia who scored below par on both reading and IQ might not be identified as having the condition. By taking the "brain-based content" out of the equation, this should catch more people who need support.
It isn't considered in isolation though – reading and spelling over time, after teaching, matters too. The authors of the new definition say IQ tests should no longer be needed, and that reading assessments are more useful on their own.
"Because the definition emphasized IQ tests so heavily, every state and school has used them to diagnose, and hopefully that will be one of the big changes we see," says Joshi.
The updated definition is also broader when it comes to the causes of dyslexia. The older guidelines suggested the condition was "neurobiological in origin", and while that isn't going away, factors like genetics and environmental influences are now also mentioned.
There's also more weight given to research from countries where English isn't the primary language. English is a bit of an outlier in terms of how difficult it is to figure out spellings and sounds – with "cough" and "rough" and "plough" for example – which needs to be taken into account compared to other languages when assessing dyslexia.
"If you look at the committee members of the International Dyslexia Association in 2002, there are many well-respected individuals, and every one of them is a Caucasian male, with the exception of one woman," says Joshi.
"Since 2002 we have had more research findings on dyslexia in languages like Chinese, Japanese, Hebrew and Arabic."
Another key component of the new definition document is an emphasis on early intervention. The sooner dyslexia can be spotted and the sooner specialized support can be put in place, the better. Having trouble with speech or being slow to start talking are potential indicators of dyslexia, though they don't guarantee a child has it.
"There can be clues that a child has dyslexia before they enter the classroom," says Joshi.
"There are specific trainings that can be applied early on, and there are certain aspects in the classroom that you need to emphasize and concentrate more on."
This new definition is advisory rather than definitive, but the team behind it is hoping it makes a significant difference in the way that schools, healthcare professionals, and governments consider the condition – and improves help for people with dyslexia.
"The previous definition was a good definition based on the research at that time, but I think some of the biggest weaknesses were its emphasis on brain function and it was mainly based on English or Western European alphabetic writing systems," says Joshi.
"This deserves attention because there hasn't been an update since 2002."
The research has been published in the Annals of Dyslexia.
This article was fact-checked by Fiona MacDonald and edited by Fiona MacDonald. While we pride ourselves on our process, we are only human. If you spot a mistake, please let us know.