ON THE CORRELATION OF MECHANICAL AND OPTICAL-PROPERTIES OF CATARACTOUS EYE LENS NUCLEI

It is investigated whether mechanical properties of human cataractous eye lens nuclei can be assessed by their optical ones. This question i s of importance as the success of phacoemulsification surgery among ot her criteria depends on the mechanical properties of the lens nucleus. The mechanical and optical properties of senile cataractous human eye lens nuclei were tested in vitro after extracapsular cataract extract ion. A new measurement system was developed to determine their mechani cal response. Hereby, a force is applied to the specimen and the resul tant displacement is measured or vice versa. Stiffness and ultimate st rength of the material are determined. Optical transmission is detecte d in dependence of Light wavelength by a spectrophotometer. In additio n the nuclear colour is determined. The correlation of mechanical stif fness and strength via optical transmission at 550 nm and nuclear colo ur is analyzed. Human eye lens nuclei show a viscoelastic mechanical b ehaviour. Measurement of stiffness is reproducible after 5-6 loading c ycles when a steady-state is reached. Mechanical and optical propertie s correlate weakly but significantly. Stiffness and strength increase with increasing nuclear coloration. Alterations of mechanical and opti cal properties are caused by the same structural changes of the molecu lar components of the ageing lens. Especially lens crystallines are re sponsible for this process. Thus, it is concluded that optical propert ies can be useful to assess the mechanical response of cataractous eye lens nuclei.