Presbyopia is one age related effect every human is suffering beginning at the age of about 45 years. Reading
glasses are the conventional treatment so far. According to the Helmholtz theory the loss of accommodation in
age is due to the hardening and the resulting loss of elasticity of the crystalline lens. However the ciliary muscle
and the lens capsule stay active, respectively. Therefore a possible treatment concept is to regain the flexibility
by inducing gliding planes in form of microcuts inside the lens. The increase of flexibility in young porcine lenses
by different cutting patterns was shown by Ripken et al.1, 2 who verified the increase in flexibility by the spinning
test introduced by Fisher.3
We will present our first measurements of flexibility increase of human donor lenses. Furthermore the influence
of the laser cuts into the lens on the accommodation amplitude will be shown in a three dimensional finite-element simulation.
The most probable reason for presbyopia is an age related loss of elasticity of the lens. It progresses typically during the whole life and at the age of about 45 it leads to a considerable loss of the ability to accommodate within the next decade. However, both, the ciliary muscle and the lens capsule stay active and elastic, respectively. With respect to this, one concept is to regain the deformability of the lens without changing the capsule or zonular apparatus. Since the investigations of Ripken et al. proofed that the flexibility of the presbyopic lens tissue can be increased through the creation of fs-laser induced microcuts inside the lens, this is one possible approach to treat presbyopia. On this account a finite-element-method model with ANSYS of the human lens during accommodation will be presented. The analysis premises all lens materials to be linear elastic and allow large displacements. A first analysis of this method for the treatment of presbyopia is accomplished. Therefore the mechanical analysis of untreated and treated lens are compared. In addition ex-vivo elasticity measurements of untreated and treated lenses will be presented. As a result an improvement of the flexibility of the lens tissue is found and as its consequence a change of the lens radii of curvature is established. After suitable processing of the output data the change in optical power between untreated and treated lenses are calculated. The finite element simulation shows similar behaviour compared to the treated porcine lenses.
A finite-element-method model with ANSYS 8.0 of a 29 year old human lens during accommodation will be presented.
The required data, to draw and calculate a two dimensional, axis-symmetric model of the human lens is inherited from
various sources. Furthermore the analysis premises all lens materials to be linear elastic and allows large displacements.
A first analysis of a possible method for the treatment of presbyopia by fs-laser induced microcuts is accomplished.
Therefore a mechanical analysis of an untreated and a treated lens are compared. As a result an improvement of the
flexibility of the lens tissue is found and as its consequence a change of the lens' radii of curvature is established. After
a suitable processing of the output data a linear Gaussian ray trace is performed and a minor change in the optical power
between the untreated and treaded human lens is perceived. By calculation of the discrete optical power of the anterior
and posterior surface on the one hand and the overall optical power on the other hand an interpretation of the
effectiveness resulting from the treatment is offered. It is ascertained that the change in optical power of the anterior lens
surface is increased while the optical power of the posterior lens surface is decreased, almost compensating each other.
A possible explanation for this phenomenon is given and a suggestion of how to increase the effectiveness of the
treatment is discussed.
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