"Dyslexia is a specific learning disability in reading. Kids with dyslexia have trouble reading accurately and fluently. They may also have trouble with reading comprehension, spelling and writing"(https://www.understood.org/en/learning-attention-issues/child-learning-disabilities/dyslexia/understanding-dyslexia).
" t is not uncommon for children with dyslexia to also have difficulties with mathematics. However, dyslexia and mathematics disorders, also known as dyscalculia, do not always come together and they might show separately with different underlying deficits or origins. Both disorders have a neurobiological origin and are related with a specific difficulty in the learning and mastering, or acquisition, of an academic skill (reading and mathematics respectively)"(https://www.dynaread.com/dyslexia-and-math-struggles-how-do-they-relate).
Have you seen: Annals of Dyslexia; An Interdisciplinary Journal of the International Dyslexia Association. (https://link.springer.com/journal/11881) There are many, many things in here which will likely be of interest. However, in 2003 the work of Reid-Lyon et. al. was published entitled; "A definition of Dyslexia" (Article A Definition of Dyslexia