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L.S. Kwok, B.K. Pierscionek; Lens Stress Forces in the Aging Human Lens Anterior . Invest. Ophthalmol. Vis. Sci. 2006;47(13):5853.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate the effect of lens growth on the spatial distribution of biomechanical forces in the aging human lens capsule.
The anterior human lens capsule was modeled using thin shell theory and biometric values from Brown (1973). An ellipsoid of revolution was used to represent the human lens. To simulate aging, a diameter of 8.9 mm (young adult) was increased to 9.2 mm (presbyopia) and the sagittal half–thickness was increased from 1.6 mm (young) to 2.05 mm (presbyopia). Radial (meridional, N<font face="symbol">f</font> ) and hoop forces (Nθ ) were calculated and normalized to internal lens pressure (Kwok, Pierscionek ARVO 2005).
The tensile radial forces N<font face="symbol">f</font> within the central zone attained a maximum ratio of young/presbyopic of 1.2 ± 0.12 at the anterior pole (<font face="symbol">f</font> = 0°) to 1.0 ± 0.1 at approximately <font face="symbol">f</font> = 40° ± 5° through to the equator (<font face="symbol">f</font> = 90°). The ratio of hoop forces Nθ remained within the band 1.2 to 1.8 from pole to the equator, except for a large peak ratio of 80 at <font face="symbol">f</font> = 30° ± 3°.
These results indicate that radial forces imparted to the central anterior lens are diminished by lens growth with the largest effect at the anterior polar region. The hoop forces also show an age–related decrease, with a slightly larger effect at the equator. In contrast to the pattern of radial force change, a large age–related decrease in hoop forces was found at an azimuth angle of 30° from the anterior polar axis. These results indicate that radial and hoop forces in the growing human lens display spatially varying but differing patterns of change. The peak change in hoop forces is consistent with a larger capsular thickness in this region and may be involved in the development of lens shape and function.
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