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Reading, contrast adaptation and accommodation in young adult myopes and emmetropes

By Colm McGonigle


Numerous reports associate prolonged periods of near-work and specifically reading with\ud myopia development. The exact mechanisms that underpin this relationship are however,\ud unclear. Reading may induce perceptual adaptations, specifically changes in contrast\ud sensitivity and to the accuracy of the accommodation response. Reduced contrast\ud sensitivity and accommodation may degrade retinal image quality which could result in a\ud stimulus to ocular elongation and therefore myopia.\ud The experimental work undertaken in this thesis investigated whether reading text on a\ud screen influenced changes in contrast sensitivity (contrast adaptation) and accommodation\ud differently in young adult emmetropic and myopic participants. Contrast adaptation was\ud examined for spatial frequencies, including those created by text rows and character\ud strokes, and accommodative accuracy was determined before and after reading.\ud Furthermore, the influence of cognitive effort on such changes was explored by comparing\ud adaptation to an incomprehensible phase randomised stimulus that otherwise shared the\ud statistical properties of the text stimulus.\ud Reading text on a screen induced contrast adaptation at the spatial frequency created by\ud text rows and myopic participants incurred more than twice the adaptation of emmetropes.\ud Contrast adaptation was not significant at the spatial frequency created by character strokes\ud in either participant group. Myopic participants had significantly greater accommodative lag\ud (reduced accuracy) than emmetropes after reading text. Myopes also showed a significant\ud increase in accommodative lag after reading.\ud There was no significant change in contrast sensitivity or accommodative accuracy after\ud participants viewed the phased randomised stimulus.\ud Text stimuli are inherently dominated by low, narrowband and orientation constrained\ud spatial frequencies generated by row of letters and inter-row space. The results presented\ud show myopes to be more susceptible to adaptation to these specific text characteristics as\ud a consequence of active reading. However, there is extensive scope for further work to\ud determine precisely why this is the case and how such changes may engender myopia\ud development

OAI identifier: oai:arro.anglia.ac.uk:702767
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