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J.R. Kuszak, M. Mazurkiewicz, L. Jison, R.K. Zoltoski; Progressively More Complex Star Sutures Formed in Primate Lenses During Periods of Development, Growth and Aging Are Related to Accommodation . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1974.
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© ARVO (1962-2015); The Authors (2016-present)
The purpose of this study was to quantitatively analyze the structure of primate lenses during the periods of embryonic development, infancy, young and middle age to show that the progressively more complex iterations of star sutures formed throughout life enable and enhance accommodation.
Gross lens dimensions (thickness [antero–posterior axis] and width [equatorial axis]) were taken under a stereo surgical dissecting microscope. Fiber dimensions were recorded from scanning electron, light and transmission electron micrographs. Scale 3 and 4D (animations) CADs of lenses were derived from micrographs.
Throughout the embryonic period primates develop and grow a Y suture lens. At birth the ant r = 1100µ, post. r = 1900 , equatorial r = 3000µ). These dimensions are the result of non–meridian fibers of unequal length and taper (28 and 43% taper in width and 63 and 37% taper in thickness at respectively the ant. and post. ends) becoming arranged end–to–end as Ysuture branches in concentric growth shells. But, after birth, the lens continues to develop and grow with two fundamental changes in its architectural scheme. First, fiber width flares instead of tapering. Anterior fiber width flare is 143, 215 and 286% and posterior fiber width flare is 115, 172, and 229% by the end of respectively infancy, young adulthood and middle age. During the same time periods, fiber thickness tapers by ∼ 65% anteriorly and ∼35% posteriorly. Second, whereas the amount of opposite fiber end curvature varies by as much as 12% at birth, the amount of opposite end curvature in fibers formed throughout infancy, young adulthood and middle age, is respectively only 0 – 8%, 0 – 6%, and 0 – 4% respectively during the same periods.
At birth primate lenses are comprised of simple coil–like fibers of variable diameter arranged as Y sutures in each growth shell. After birth, new cortical fibers are added that have reduced end opposite end curvature, or are more leaf spring–like, with significantly wider and thinner ends, arranged as simple 6 branch star sutures during infancy, 9 branch star sutures during young adulthood, and 12+ branch complex star sutures from middle age and beyond. In this manner, cortical fibers with structure and organization progressively more conducive to accommodation, enhance dynamic focusing by allowing for increases in lens thickness and surface curvature due to interfacing of fiber ends at sutures, sufficient to produce a change of as many as 16 diopters.
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