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J. P. McDonald, P. L. Kaufman, M. Croft; Accommodative Lens Thickening vs. Centripetal Movements of the Lens Equator and Movements of the Ciliary Body. Invest. Ophthalmol. Vis. Sci. 2010;51(13):800.
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© ARVO (1962-2015); The Authors (2016-present)
Our goal was to determine the age-related changes in ciliary body forward and centripetal movements in relation to lens equator and lens thickening movements during accommodation in rhesus monkey eyes.
Coincidence refractometry was used to measure the refractive power of the eyes before and during electrical stimulation of the Edinger-Westphal (E-W) nucleus to induce accommodation. Accommodative movements of the ciliary body were measured by UBM and goniovideography. Lens thickness and lens equatorial movements were measured by ultrasound biomicroscopy and goniovideography, respectively. The decrease in lens diameter during accommodation was calculated from the sum of nasal and temporal lens equator movements. The eyes of 8 rhesus monkeys, aged 5-20 yrs, were studied.
Maximum accommodative lens thickening declined significantly with age (-0.040 ± 0.008mm/year; p=0.003; n=8) and lens thickening was significantly related to accommodative lens diameter change (1.51 ± 0.59 mm lens thickness change/mm lens diameter change; p=0.044; n=8). In 4 young eyes, the maximum accommodative lens diameter decrease (narrowing) was 0.58 ± 0.074 mm, similar in magnitude to the maximum accommodative lens thickening, 0.66 ± 0.059 mm, and both parameters changed in a parallel fashion with varying levels of accommodation. In 2 older eyes, the maximum accommodative lens diameter narrowing was 0.40 ± 0.066 mm, a 30% decline in movement compared to the young eyes. Maximum accommodative lens thickening in the older eyes averaged 0.22 ± 0.081 mm, a 67% decline in thickening compared to the young eyes.
The fact that accommodative lens thickening declined with age more markedly than accommodative lens diameter narrowing could be due to simple geometric / biophysical necessity and/or aging changes inherent in lens structure. Age-related changes in accommodative lens thickening may not be the same quantitatively or mechanistically as the age-related changes in accommodative diameter narrowing, regardless of the ciliary body state of contraction. In addition, the ability of the ciliary muscle to maintain some centripetal movement while undergoing a dramatic loss in forward movement with increasing age may also have an impact on differential lens shape changes (i.e.,accommodative thickening vs.equatorial movements). Whether the age-related differences in lens thickening vs lens equator movements are due to the lens itself or to changes in ciliary body movements, these findings may provide insights into successful accommodating IOL design.
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