Visual Loss in Down Syndrome: Investigating Cortical, Retinal and Ocular Contributions to Poor Visual Performance

Down syndrome is the most common genetically based cause of intellectual impairment in children. Woodhouse et a/. (1996) have established that visual acuity is reduced in Down syndrome. In a recent study, Woodhouse and colleagues compared objective acuity measurements recorded with visual-evoked potentials (VEPs) with behavioural tests of acuity in both Down syndrome and control subjects. They found both VEP and behavioural measures were significantly poorer in the Down syndrome subject group (John et a/., 2004). Woodhouse and colleagues hypothesise that an underlying sensory defect exists.This thesis investigates the relative roles of optical, retinal and cortical factors contributing to this underlying deficit in Down syndrome. Psychophysical methods were used to measure grating resolution, interferometric and vernier acuity. Grating resolution acuity is limited by the optical and retinal I resolution of the eye. Interferometric acuity measures the retinal resolution limit, and vernier acuity is thought to reflect the integrity of the primary visual cortex.EThOS - Electronic Theses Online ServiceGBUnited Kingdo