Frequency of reading disability caused by ocular problems in 9- and 10-year-old children in a small town

In most children referred to our department with a diagnosis of dyslexia, we have found an ocular disorder that had not been detected during previous ophthalmologic examinations. Exophoria and/or hypoaccommodation were the most common cause. Some of these children needed eye muscle surgery to improve the reading problems. However, these patients represent a selection. Therefore, we performed a field study to determine the percentage of children with reading disability caused by ocular disorders and the percentage of children with real dyslexia in a normal population. This was made possible by an examination of most pupils in the 4th grade of the three primary schools in a small German town. The co-author and a very experienced orthoptist performed all of the examinations.

Eighty-nine out of 127 children were examined. Of these, 16 (18%) had reading problems (2 girls and 14 boys). Most of them had accommodation problems: six (6.7%) suffered from an uncorrected hypoaccommodation, three children did not wear their prescribed glasses, one child had not been prescribed any glasses yet and one child had the wrong glasses. Two children suffered from pathophoria: one from eso- and the other from exophoria compensated by accommodative convergence. In 3 (3.4%) children no ocular cause could be found. These children may have true dyslexia.

Of the 89 children examined, 16 (18%) had reading problems and only 3/16 had no detectable ophthalmologic explanation. Hypoaccommodation was the most common cause of reading problems (in 6 of 16). In most of the cases it had not been diagnosed before. In all of these children the reading ability improved markedly with the proper refractive correction, bifocals or prisms.