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Mitchell George Nye-Wood, Alyssa Lesley Lie, Paul J Donaldson, Ehsan Vaghefi; Physiological optics of the accommodating lens: a clinical observational study using MRI. Invest. Ophthalmol. Vis. Sci. 2018;59(9):4975. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
The ageing process has profound effects on vision, causing a hyperopic shift in visual acuity (VA) and a reduction in accommodative amplitude (AA) that leads to the diagnosis of presbyopia. Contributing factors include age-related increases in the thickness, stiffness and water content of the lens, and an altered refractive index (RI) profile with age. By taking eye exams and clinical MRI measurements of the lens of young and old individuals, we investigate accommodation, and the pathoetiology of presbyopia
18 subjects were recruited and categorised as ‘young’ (aged 20-30) or ‘old’ (aged 45-55). Best-corrected VA was measured for each patient at 6m distance and the best eye was selected for future analysis, or the right eye if both eyes satisfied the exclusion criteria. Eye dimensions and AA were recorded, and monocular near VAs were measured at 40cm while wearing distance correction. Later, participants were fitted with MRI-compatable glasses which allowed the chosen eye to be corrected for distance vision and the other to be eye covered to ensure monocular vision and maximise the accommodative stimulus. Lens geometry, T1 and T2 maps were recorded, initially while fixating on a target 4.5m away, and again while fixating on a 40cm distance target that was resized so as to be just resolvable with their measured near VA. Gradients in T1 and T2 were modelled with an exponential function to enable comparison
We observed significant differences between young and old lens size, shape, AA, and deformability. In young lenses, accommodating from 4.5m to 40cm caused the anterior surface to become more curved (p=0.026), and the lens to become thicker (p=0.008). Linear regression shows AA in the young lens is correlated to the change in anterior surface curvature (p=0.022), and to the change in T2 value in the lens nucleus (p=0.014). The old lens is thicker (p<0.01) and more curved at the anterior surface (p=0.021) than the young lens, with a flatter gradient in T2 in the equatorial plane (p<0.01). Accommodation did not elicit a significant change in shape in the old lens
AA is strongly correlated with the extent to which the lens anterior surface changes curvature (p<0.01). In the young lens this occurs readily and affects nuclear T1 and T2 values, while in presbyopia the lens is less deformable, and T1 and T2 values are less responsive to optical power changes
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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