Mae'r cynnwys hwn ar gael yn Saesneg yn unig.
The Bifocal study looked at the effects of wearing bifocal spectacles on near visual functions, such as accommodation (focusing). Any ageing adult who under-accommodates when approaching middle age is familiar with the concept of bifocal spectacles to aid focusing at near, so why not offer the same aid to children with Down's syndrome who don't focus accurately? Some clinicians routinely prescribe bifocal spectacles for children with Down's syndrome, namely in Scandinavia and Canada, and find that the children comply well with the wearing of these glasses, as well as benefiting visually from wearing them. However, bifocals are not prescribed commonly in the U.K, and there have been no controlled trials examining the effects of these bifocal corrections on near functions or educational performance.
For the benefit of this study, 34 children participated. Some were already part of the existing cohort, and others were new recruits. The children were matched into 17 pairs, based on comparable visual problems, similar ages, intellectual ability and educational setting. Once a pair had been matched, one child was randomly assigned to the treatment group (prescribed bifocal corrections) and the other assigned to the control group (given new single vision spectacles).
Two researchers conducted the study, one an optometrist (Ruth Stewart) who assessed each child's visual functions, and the other a psychologist (Lidia Trojanowska) who assessed each child's cognitive ability using standardised tests. Both Ruth and Lidia obtained a baseline measurement of each child's visual and cognitive ability before the study began, and tested all the children again (after prescribing the new glasses) after 1 week, 2 (vision only), 5 and 8 months. The child's teacher also evaluated his/her progress in school tasks, as well as his/her social adjustment within a school setting at the beginning and end of the study.
Ruth's optometric and visual data has been analysed, and the results show a significant difference between the bifocal and control groups. The children accommodate much more accurately through their bifocals than do the control children through their ordinary lenses. Surprisingly, the children with bifocals also accommodate more accurately when looking over the top of their bifocals through the 'distance' part of the lens. This suggests that the bifocals are 'teaching' the children to use their own focusing ability.
None of the children experienced any adverse effects of bifocals. The bifocals were prescribed for school use only, but several of the children chose to wear them all of the time, preferring them to their conventional glasses.
We now prescribe bifocals routinely for children with Down's syndrome who under-accommodate. A new and exciting part of the longitudinal study is taking place – a follow-up of the use of bifocals and their impact on the children's 'natural' accommodative ability.
A very important aspect of prescribing bifocals for children with Down's syndrome is the fit of the segment. It is critical that the top of the bifocals is in the correct position. Full details of this are given in the 'For Professionals' section of this website.
The study was funded by The Health Foundation.