Background Down's syndrome CDS) is the most common cause of learning disability in humans. Studies have described deficits in visual performance in DS that cannot be explained by ocular pathology, refractive errors, attentional or behavioural factors. Structural differences in the optics of the DS eye have been reported. It has also been previously reported that visual performance in DS is significantly improved when the optics of the eye are by-passed, suggesting an underlying optical defect. This thesis investigates whether optical quality is reduced in children with DS and how an optical deficit might influence their visual function. Methods Forty-four children with DS and 211 age-matched typically developing children participated in the main study. Optical quality was quantified by the measurement of higher order aberrations. Ocular structure and shape were also assessed to explore their influence on higher order aberrations and optical quality. Higher order aberrations were compared with visual performance measures of high and low contrast recognition acuity, grating resolution acuity and accommodative function. Higher order aberrations were also analysed for a large group of typically developing white Northern Irish children to explore the influences of age and refractive error on these measurements. Results & Conclusions The data demonstrated that: • Children with DS have greater levels of higher order aberrations and poorer optical quality than typically developing children. These differences were not attributable to greater levels of ametropia or premature aging in DS. • The data suggest multiple limitations of visual function in children with DS including optical and neural factors. • Neural adaptation and compensation of retinal image blur may be lacking or less efficient in DS resulting in poorer visual performance. • Negative spherical aberration found in the children with DS may indicate that differences in crystalline lens shape may restrict accommodative ability.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:589518 |
| Date | January 2011 |
| Creators | McCullough, Sara |
| Publisher | University of Ulster |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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