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Robert Kammel, Stephanie Bühren, Roland Ackermann, Stefan Nolte, Andreas Tünnermann; Direct Measurement Of Lens Tissue Stiffness Reduction Induced By Femtosecond Laser Treatment. Invest. Ophthalmol. Vis. Sci. 2011;52(14):849.
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To renew flexibility of the aged lens as a treatment for presbyopia, decrease of lens stiffness was investigated for different spot patterns induced by fs-laser treatment of the crystalline lens.
To measure the resistibility of porcine lenses before and after fs-laser treatment extracted lenses were placed on a lens holder on an analytical balance within 12 hours post-mortem. Lenses were pressed against a contact glass with less than 20 mN creating a low deformation. Forces transferred by the elastic lens tissue were measured and recorded automatically. After reaching a pre-assigned load, patterns of up to 2 million separate disrupted spots were applied using a fs-laser system attached to a 3D-galvano-scanner. Pulse energy was kept slightly above the threshold of laser induced optical breakdown to avoid the formation of cavitation bubbles. Measurements for different laser patterns and numbers of applied spots could be realized.
The presented setup allows direct measurement of reduced lens stiffness within the same lens avoiding complex statistical comparison of laser treated and untreated lenses. After applying low pressure the relaxation of lens tissue causes a slow decrease of the measured load. Instantaneously after laser treatment the measured forces drop by up to 10 % caused by the change in lens structure, even in young flexible porcine lenses. The decrease of the measured load after treatment shows a linear dependency on the total number of applied laser spots placed within the lens nucleus.
We have evaluated the influence of fs-laser treatment onto stiffness of porcine lenses that scales almost linear with the number of applied laser spots. To increase lens flexibility and to renew accommodation, applying multiple layers of separate disrupted tissue spots within the lens nucleus appears to be a promising treatment for presbyopia.
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