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R. Ackermann, R. Kammel, S. Nolte, T. Peschel; In-vitro Measurements on the Effect of Different Fs-Laser Patterns on the Lens Flexibility. Invest. Ophthalmol. Vis. Sci. 2009;50(13):6134.
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© ARVO (1962-2015); The Authors (2016-present)
The most important cause for the development of presbyopia is the hardening of the crystalline lens, for which a satisfactory treatment has not yet been established. Among the variety of approaches to restore accommodation we investigate the enhancement of the lens flexibility by the application of ultrashort laser pulses. This work compares the effect of different cut patterns based on finite element analysis.
Porcine eyes were dissected within 72 hours post-mortem by extracting the lens within the ciliary body, which was then attached to the clamps of a lens stretching apparatus in order to exert and measure forces to the ciliary body. The laser effect was evaluated by comparing laser structured with untreated lenses of the same individual, and statistical validation was performed on 30 eyes. The laser system provides pulses with a duration of 400 fs with an energy of up to 5 µJ at 200 kHz. A downstream scanner system allows writing three dimensional structures with a focal spot size of less than 10 µm.During the stretching procedure the lens shape was evaluated by a rotating Scheimpflug-camera that allows determining the lens diameter and thickness. The lenses were optically measured by a Shack-Hartmann sensor placed downstream from the stretcher characterizing a transmitted probe light.
Previous in-vitro experiments showed an enhancement of the lens flexibility when the laser spots cover approximately the whole lens, yet optical characterization is hampered by light scattering of the transmitted probe light.In order to reduce this effect we investigated two different cut patterns based on finite element analysis. A theoretically promising approach is to separate the core from the lens cortex. Lenses to which this pattern was applied could be reproducibly characterized by the wave-front analysis, yet the effect on the lens elasticity is below statistical significance. As a second approach, several layers were applied within the lens core in a defined distance to each other. In this case, the evaluation of 30 lenses shows an average increase of accommodation width of about 2 dpt relating to the aqueous storage environment. Remarkably, one has to consider that this value was achieved by treating comparatively soft porcine eyes.
We have compared different laser cut patterns. They take into account the light scattering induced by the applied laser spots. Among those, the placement of a few layers within the lens core are the most promising. Further experiments will validate these results on presbyopic human lenses.
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