Longitudinal study
Why track children's eyes with time?
Very little was known about the eye development of children with Down's syndrome. It was important to find out if the eyes of our children underwent the same biological changes, as this hugely impacts upon the provision of spectacles.
All children involved in the Down's Syndrome cohort have been seen regularly either at home, school or here in the School of Optometry and Vision Sciences, in order to monitor both their visual and cognitive development. Since 1992, all children in Cardiff diagnosed with Down's syndrome have also been invited for vision testing by Maggie at Cardiff University.
Refractive error
The vision data obtained from these visits over the years show that many of the children have refractive errors (long- or short-sight). Refractive errors are quite common in early infancy in all children. The usual course of events is for children to grow out of their errors over the first four years of life. We have found that children with Down's syndrome begin with the same range of errors as other children, but instead of growing out of them, many of the children develop larger refractive errors as they get older. This means that many children with Down's syndrome need to wear glasses by the time they get to school age. Most of the children who wear glasses are long-sighted, but some children are short-sighted.
Eye alignment
The longitudinal study also shows that children with Down's syndrome have a higher prevalence of oculomotor problems, for example strabismus (squint) (24%), and nystagmus (wobbly eyes) (14%). The data have also highlighted a relationship between accurate focusing, strabismus and significant long-sight. Those children who can focus accurately are less likely to have a squint, and less likely to be long-sighted.
Accommodation
Another major finding that emerged from the longitudinal data is that most children (73%) with Down's syndrome under-accommodate (inaccurately focus) at near. Those individuals who under-accommodate continue to do so, even when their refractive errors are corrected with spectacles. Thus, most children with Down's syndrome have a constant retinal blur for all near work, which may have an adverse effect on the children's ability to discriminate fine detail at near. Since our 'Bifocal Study' was completed, we now routinely prescribe bifocals for children who under-accommodate. In the study, we are now monitoring the longer-term effects of bifocals, and the numbers of children who are able to dispense with them over time and return to 'ordinary' glasses.