Bifocals in children with Down syndrome (BiDS)

Abstract

Down syndrome (DS) is the most common genetic cause of mental challenge in individuals and is associated with many ocular disorders. One of these anomalies which is frequently present in this population is reduced accommodation and many studies have reported this. Accommodation is the ability of the crystalline lens in the eye to focus for objects at different distances. Prescribing bifocals could potentially help in correcting the resultant inaccurate focus, although this modality of treatment is not very commonly practiced. The impact of bifocals on reading and literacy skills (academic skills) as well as visual-perceptual skills in individuals with DS has not been studied previously. The aim of this study was to investigate the impact of bifocals on the educational attainment of children and young adults with DS who have reduced accommodation and monitor their performance longitudinally. This is the first time that the impact of bifocal provision on the functional performance of children and young adults with DS has been studied. Also for the first time in children with DS, frequent measures of performance have been used to control for progression with time before and after bifocal prescription. A battery of tests comprising early literacy and visual-perceptual skills was administered before and after bifocal prescription. Accommodation and printing skills were also measured periodically. It was expected that the prescription of bifocals would help to improve near visual acuity and that the improved near acuity would result in educational achievements at school. Compliance with spectacle wear and school reports were also considered. A longitudinal observational study design was utilized with each child acting as his/her own control. Fourteen children and teenagers aged 8-18 with DS were recruited and underwent a basic optometric exam including measurement of their accommodative ability and a cycloplegic refraction. Seventy nine percent required a change in their spectacle prescription and were prescribed single vision (SV) lenses. One hundred percent had reduced accommodation both before and after new SV glasses were prescribed. Distance visual acuity did not significantly improve with SV lenses (p>0.05) but near visual acuity showed a significant improvement (p-=0.015) from 0.64±0.25 logMAR to 0.54±0.20 logMAR. A high prevalence of high refractive errors, including both hyperopia and myopia, was observed t andnear visual acuity even with a habitual correctionwas reduced compared to distance VA. A full battery of reading and visual-perceptual tests was administered with SV lenses. Thereafter the participants were followed for 6 months and monthly subtests (probes) of literacy skills and printing tasks were administered. These “probes” acted as immediate indicators of the child’s performance with his/her correction and change in performance over this time period was monitored. Over the 6 months the participants showed no noteworthy progression in their literacy skills. The group of participants performed at an age-equivalent between 3-10 years. The quality of printing formation in this population has been studied for the first time and showed no significant change over time. It was observed that some aspects of visual-perceptual and early literacy skills could be measured in all the participants. Chronological age and receptive vocabulary were significantly correlated with visual motor integration and Word Identification. Eighty five percent of the participants were prescribed bifocals with additions ranging from +1.00D to +3.50D at the 6th month after the provision of SV lenses. Post-bifocal measures of visual acuity, accommodation, visual-perceptual and early literacy skills were taken 1-2 weeks, and finally 5 months, after bifocal correction. Throughout the pre- and post-bifocal period, verbal compliance with spectacle wear was assessed through school and parental reports. The mean near logMAR VA improved with bifocals (p=0.007) compared to SV lenses. Accommodative accuracy improved with bifocals (less accommodative lag) compared to SV lenses (p=0.002) but there was no change in the accommodation exerted through the distance portion of the lens compared to SV lenses (p=0.423). There was a main effect of bifocals on sight words (p=0.013), Word Identification (p=0.047), and 2 out of 3 tests of visual perception (p<0.05). It was observed that bifocals have a positive impact on the children’s visual and school performance and this was supported by reports of improved performance in school for nine out of eleven individuals who were prescribed bifocals. The children adapted to bifocals more readily than the SV glasses, wearing them for the majority of their waking time. All the sessions of early literacy and visual-perceptual skills administered throughout the duration of the study were videotaped and were then analyzed by a naïve examiner. The time taken to perform each task was calculated and compared between the main single vision and bifocal visits. There was a significant decrease in the completion times on the test battery with bifocals for Word Identification (p=0.0015) and the Dolch sight words (p=0.048). All participants who completed the monthly probes took less time to complete the Dolch sight words (p= 0.025) and the number writing task (p=0.001) with bifocals. Similar results were not observed for the visual-perceptual tests. Performance in the monthly probes was compared before and after bifocal prescription in terms of the average raw scores and time taken. The rate of improvement in performance with bifocals was calculated by plotting the test scores against time and determing the regression lines. There was an overall significant improvement in the monthly probe scores of Word Identification (p=0.050), Dolch sight words (p=0.025) and the number test (p=0.023) with bifocals. The rate of progression in scores increased with bifocals for the Word Identification (p=0.008). Evidence of improved and faster performance with bifocals on some literacy skills was seen. It was concluded that bifocals, which result in improved near focusing, help individuals with DS to maximize their educational potential. It is suggested that more children and teenagers with DS will benefit from bifocal prescription, as they were observed to improve near visual acuity and enable better focusing for near. This thesis has provided a comprehensive analysis of the some tests of literacy, visual- perceptual and early printing skills before and after a bifocal prescription in a group of children and teenagers with Down syndrome. This is the first study to longitudinally monitor the educational impact of bifocals in a population with Down syndrome. Furthermore, the quality of printing formation in this population is a previously unstudied area and was studied longitudinally prior to and after bifocal intervention. The impact of bifocals on printing skills is also discussed. Another novel approach was that all the literacy, writing and visual-perceptual tasks sessions were videotaped to calculate the time taken to complete each task pre- and post-bifocals. This thesis is an addition to the existing literature on bifocal prescription in Down syndrome populations. From the findings in this thesis, the following recommendations are made in order to improve the standard of clinical eye care in this population. Measurement of accommodation should be considered a routine test in the clinical ocular examination for young individuals with DS, now that it is known that many of them present with accommodative deficits. When accommodation is found to be reduced, prescription of bifocals is indicated and should also become the standard of care in this population.