Anatomical and Optical Correlates of the Peripheral Retina in Myopia

  • Lorraine A. Cameron

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)

Abstract

Myopia has emerged as a major public health concern due to increased prevalence, particularly in East Asia, in recent years. The development and progression of myopia is complex and due to genetic and environmental factors and the interaction between them. Much research has investigated the role of near work, the accommodation response and resultant defocus on myopic development. Investigations of defocus across the peripheral retina and the influence on myopic development have been of interest in recent years. Within this thesis various optical and anatomical aspects of the central and peripheral retina have been investigated in emmetropes and myopes to identify differences that may aid the understanding of myopic development.

Accommodation microfluctuations remain unchanged when information contained within the central part of a stimulus is optimal (4cpd) regardless of the details within the peripheral part. When information contained within the central part of a stimulus is blurred (0.5cpd), as long as there is some clear (4cpd) peripheral information present within the central 8° of the stimulus, myopes will utilise this to regulate the accommodation response and have reduced microfluctuations. Emmetropes may not utilise this peripheral information, or else the accommodation microfluctuations of the emmetropes cannot become any smaller, for example due to anatomical restrictions. Accommodation response thresholds increase with increasing eccentricity in emmetropes and at a faster rate in themyopes. The increased magnitude of the accommodation response thresholds could explain why myopes have increased accommodation microfluctuations with increasing eccentricity.

Measurements of defocus during near viewing and an increased accommodation response results in increased hyperopic defocus centrally and peripherally and the magnitude of the hyperopic defocus is greater across the retina in the myopes compared to the emmetropes. This defocus is a potential trigger for eye growth and can also be used to infer the shape of the eye, suggesting that myopes have prolate shaped eyes and emmetropes more oblate shaped eyes. This is confirmed by measures of peripheral retinal shape by means of peripheral eye length measurements where there is nasal temporal asymmetry in the shape of the retina in myopes but not in emmetropes. Retinal shape differences suggest a regionally selective mechanism in eye growth in myopes and that the eye expands more axially and less so globally.

Results from experimental chapters within this thesis have allowed the application of refractive group data to a theoretical model of a realistic near visual scene in emmetropic and myopic subjects. This model has provided a unique insight into the magnitude of defocus the emmetropic and myopic eye is exposed to in a normal viewing situation whilst taking into account the individual anatomical variations in eye shape, measurements of defocus across the retina and sensitivity to defocus.
Date of Award2013
Original languageEnglish
Awarding Institution
  • Glasgow Caledonian University
SupervisorMhairi Day (Supervisor), Lyle Gray (Supervisor) & Dirk Seidel (Supervisor)

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