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Age-related changes in the optics of human eye with accommodation
[Thesis]. Manchester, UK: The University of Manchester; 2017.
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Abstract
PURPOSE: The mechanism of accommodation together with its age-related changes is complex and still not fully understood. The objective of this PhD thesis is to extend this knowledge and evaluate the accommodative performance with some options for presbyopia correction available at present. METHODS: The latest technology was used to assess the accommodative function both from a structural and optical point of view. Corneal and ciliary muscle changes with accommodation were evaluated in the first two experimental chapters. Chapter 3 combined imaging data of the ciliary muscle with information of the optical response to different accommodative demands in an age divided cohort, whose accommodative response was analysed in a static and dynamic way in Chapter 4. Fluctuations in accommodation and dissaccommodation and time constants were measured in natural conditions. Additional dynamic (Chapter 4) and static (Chapter 5) assessment of the accommodative performance was done for young subjects fitted with multifocal contact lenses (MFCLs). RESULTS and CONCLUSION: Cornea is stable during accommodation while the ciliary muscle thickness varies at different accommodative demands but not as a consequence of ageing. Microfluctuations in accommodation show highly intra-subject variability, but a trend to play a role in accommodation control can be observed. In general, a bigger magnitude of fluctuations is found when accommodation is more accurate. Ageing has a significant effect on the accommodative fluctuations when a small stimulus (2.5 D) is presented but not on time constants. Subjects in the third decade of life present the highest magnitude of accommodative fluctuations as their accommodative system is more stressed. Multifocal contact lenses fitted in young subjects do not affect the accommodative dynamics. Some improvements have been seen when different generations of multifocal contact lenses are assessed. The applicability of this research to the improvement of solutions capable of restoring the accommodative ability in older eyes, widens the future scope of this research.