Femtosecond Lentotomy: A Prospect for a Treatment to Regain the Accommodation Ability

Abstract

Presbyopia is the age-related loss of the accommodation of the lens of the eye which affects every person in the fifth decade of life. When presbyopia occurs, continuous growth of the lens fibers results in sclerosis of the lens tissue which is accompanied by a decrease in flexibility. Initially, this impairs the dynamic adaptation from far- to short-sightedness, until ultimately it fails completely. Currently, the conventional approach to compensate for the loss of accommodation is the use of reading glasses for short-sightedness. Although new surgical treatment methods have been developed, so far none of them allow a dynamic accommodation. An alternative approach is the restoration of the flexibility of the lens using a procedure based on the non-linear interaction of ultrafast laser pulses and tissue. The non-linearity of the photodisruption effect can be used to create micro-incisions inside the lens without opening the eye globe. These defined gliding planes thereby restore the lost flexibility. This treatment method, known as fs-lentotomy, enables regeneration of real dynamic accommodation. The fs-lentotomy treatment technique as well as the effect of laser irradiation on the tissue was evaluated. For the first time, various 3-D structures for gliding planes were successfully generated in experiments with human donor lenses of different ages. An average increase in anterior-posterior lens thickness of 100 μm accompanied by a decrease of equatorial lens diameter was observed as a direct consequence of fs-lentotomy. This is attributed to increased flexibility, as the force of the capsule bag deforms the lens tissue to a higher degree. Using the Fisher’s spinning test, a 16 % average flexibility increase was ascertained in human donor lenses. The control of the position of the gliding planes was found to be extremely important for safe and successful surgery. In addition to the experiments, calculations of the biomechanics during accommodation were carried out using the finite element method. This indicated that the achievable increase in flexibility of the lens depends on the applied cutting pattern. In vivo experiments with the lab prototype surgical instrument showed that laser incisions inside a rabbit eye lens caused no growing opacification (cataract ) over a 6 month follow-up period. However, the incisions were still detectable using Scheimpflug imaging and histopathological techniques, although the visibility of the incisions was declining. No distinctive features were observed upon evaluating thermal exposure of the rabbit retina during fs-lentotomy. It is expected that no damage will occur in the human retina, as exposure of the human retina is lower than exposure of the rabbit retina, due to the larger human eye bulb. The basic scientific investigations of fs-lentotomy show that it is possible to recover the flexibility of ex vivo human donor lenses. Consequently, the requirements for regaining a dynamic accommodation exist. Furthermore, no side effects were observed during the wound healing process and during a 6 months follow-up period. Based on the presented findings, it can be concluded that fs-lentotomy has the potential to become a well suited procedure for the treatment of presbyopia.