Visual development and visual defects in children with Down's syndrome

This thesis investigated the refractive, accommodative and colour vision status of young people with Down's syndrome (DS). Seven separate studies were conducted. Participants were recruited from the Cardiff Down's Syndrome Vision Research Unit. Abnormal refractive development was reported from an early age, and continued through the first 15 years of life. The normal emmetropisation process was re-aligned to leave subjects with hypermetropic errors, with a wide variation in refractive error, at all ages. There was a specific development of oblique astigmatism with age, which may be associated with the reduced palpebral aperture. Parental refractive status was not found to influence that of their children with DS, although such a relationship was found with their typically developing siblings. The cause of the refractive errors was axial in nature in children with DS. However, general physical growth did not have an active influence in shaping these errors. Bifocal spectacles were found to be a successful treatment for reduced accommodation in children with DS. From the study cohort, over 40% of the children were able to effectively discard bifocal wear after gaining accurate accommodation. Children with DS demonstrated their ability to engage in subjective colour vision testing, given that appropriate tests were used. The design of the Mollon-Reffin 'Minimalist' (M-R) colour vision test was found most suitable. This test showed high sensitivity and specificity in comparison to other clinical tests. Using the M-R test, the prevalence of colour vision defects in DS was found to be comparable to that of the general population. The studies have generated optometric guidelines for the clinical care of people with DS which emphasise the importance of frequent routine clinical examination of this population due to the unpredictive nature of their refractive error development. Examination from an early age will allow for the early detection, and prompt management, of visual problems. Bifocal prescription is highly encouraged for those with reduced accommodation, with cessation of wear being decided from on-going assessment of the patient's accommodation after bifocal prescription