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Ralph Michael, Justin Christopher Christopher D'Antin, Laura Pinilla Cortés, Brian Sheil, Harvey John Burd, Rafael I Barraquer; Ex vivo simulated accommodation in human donor eyes with and without cortical cataract. Invest. Ophthalmol. Vis. Sci. 2019;60(9):3164. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
It is known, that human cortical or cuneiform opacities are accompanied by changes in lens fiber structure and architecture mainly in the equatorial border zone between the lens nucleus and cortex. Because the lens cortex and nucleus have different viscoelastic properties in young and old lenses, we hypothesized that external forces during accommodation cause shear stress predominantly at this nucleus-cortex interface and induce cortical cataracts.
We studied 9 human donor lenses in a stretching device for anterior eye segments, measuring the forces and obtaining frontal and cross-sectional images during stretching. This included 7 aged lenses with different degree of cortical cataract (60 to 88 years) and 2 young lenses (33 and 46 years). Equatorial lens diameter and relative central lens thickness changes as well as internal lens ruptures were evaluated, comparing a stretch with a standard mean force of 54 mN with the unstretched state.
Equatorial diameter increased in all lenses after stretching; by 1 to 6% in the aged lenses and by 3 to 5% in the young lenses. Central thickness remained unchanged or decreased up to 3% in 5 aged lenses and increased by 1 or 5% in 2 aged lenses. In the 2 young lenses it decreased by 5 or 9%. Four aged lenses with cortical cataracts showed ruptures at the nucleus-cortex interface adjacent to the cortical cataracts. Both young lenses as well as 3 lenses with cortical cataract did not showed ruptures.
The lens cortex is still soft in some aged lenses and can be deformed, but probably due to a stiff lens nucleus, this does not yield a reduction in central lens thickness as large as in young lenses. The stiff lens nucleus may also be the reason why some aged lenses increase central lens thickness when stretched at the equator. As the equator is squeezed, lens cortex material is pushed towards the lens pole. The nucleus-cortex interface is vulnerable and can rupture when external forces are applied. Mechanical stress in the lens induced by accommodation may contribute to the formation of cortical cataract.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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