Two-photon excited fluorescence of the lens for the diagnosis of presbyopia

Presbyopia is a wide spread phenomenon in elder people and is caused by the hardening of the lens in human eyes. Research is performed to make such lenses again more flexible by application of geometrically optimised cuts through the lens with a femtosecond-laser. Different protein agglomerations are responsible for the flexibility reduction of the lens. Two-photon excited fluorescence of the lens can be used as a diagnostic tool to localise such protein accumulations. In in-vitro experiments with human cataract lenses and also lenses of the Philly-mouse it could be demonstrated that with age the fluorescence increases as presbyopia proceeds. The distribution of the fluorescing compounds are not homogeneous but rather cloudy. Discrimination of the compounds by fluorescence lifetime measurements in relation of the depth in the lens is possible.