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M. Mazurkiewicz, M. B. Alikhan, R. K. Zoltoski, J. R. Kuszak; A Novel Method for Estimating the Rate of Human Lens Growth. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2020.
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© ARVO (1962-2015); The Authors (2016-present)
Past estimates of the rate of lens growth have generally neither completely accounted for the spatial (3D) aspects of the lens nor the fact that the lens undergoes life long growth (time=4D). The purpose of this study was to more accurately estimate the rate of lens growth in defined periods of life, by factoring in the 3D and 4D parameters.
Lens dimensions were taken under a stereo dissecting microscope as well as from scanning electron micrographs. For this study, the rate of lens growth is defined as the average time it took to form a growth shell (GS), during development (gestation), infancy (0-3), adolescence (3-15), adulthood (15-60), and aged (60+). The total membrane surface area (SA) of growth shells located every 200 mm from the embryonic nucleus to the periphery of the lens was calculated using standard formulas for SA of oblate spheroids appropriately corrected for the difference in curvature of the anterior and posterior surfaces. Rate of lens growth was determined by dividing the total membrane SA at any given point of time by the length of time it took to form that portion of lens.
During fetal development from the first to the last GS formed at birth, the SA of the lens increases from 0.6 mm2 to 78.4 mm2 (131x increase) by the addition of ~1800 GS. The rate of GS production during this period is ~12.7 mm2/hr. During infancy, the SA increases to 118.5 mm2 (1.5x increase) by the addition of ~400 GS. The rate of GS production during this period is ~1.5 mm2/hr. During adolescence, the SA has increased to 172.2 mm2 (a 1.4x increase) by the addition of ~600 GS. The rate of GS production during this period is ~0.8 mm2/hr. During adulthood, the SA has increased to 196.3 mm2 (a 1.1x increase), by the addition of ~200 GS. The rate of GS production during this period is ~0.2 mm2/hr. During further aging, the SA has increased to 207.3 mm2 (a 1.06 x increase), by the addition of ~50 GS. The rate of GS production during this period is ~0.1 mm2/hr.
The fact that lens size does not increase linearly throughout life, could lead to the conclusion that growth might actually cease by the age 40. However, when the 3D solid geometry of the lens is factored into estimates of lens growth, it can be seen that while lens growth decreases relatively linearly, it continues to grow throughout life. It is important to note that as it takes longer to form a GS as a function of time, the maturation of the fiber (elimination of organelles) will take longer. This may have important physiological implications.
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