gms | German Medical Science

Foldable Intra Ocular Lenses (IOL) are by now well established on the market. Modern keyhole surgery demands decreasing incisions and hence further decreasing injection diameters. This results in an increasing stress of the IOL material during the injection process through a cartridge. This study comparatively determines the optical imaging quality of ten different IOL types of various manufacturers. The imaging quality is measured before and after an injection through a cartridge. It is also determined weather the optical imaging quality after an injection process does reach the original imaging quality (before the injection) again.

Two different IOL of each type with different refractive powers (e.g. +13D and +26D) were measured. All analyzed foldable IOL were injected using the methods, injectors, cartages and viscoelastica according to the specifications of the corresponding manufacturer. The imaging quality was measured before and in 5 minute intervals after the injection over a maximum time of 30 minutes for each IOL. The measurement was conducted according to the EN ISO 11979-2 standard, using a measurement system based on analysis of the Point Spread Function (PSF) and Modulation Transfer Function (MTF) respectively. According to these measurements the Strehl-Ratio (SR) was determined for each individual measurement.

Especially for higher dioptres the imaging quality of the different IOL varies significantly: the Strehl-Ratio (SR) of the measured +26D IOL varied by up to 20% of the Value of the best measured IOL. The SR of the two measured aspherical corrected IOL was about 15% better than the SR of standard (spherical) IOL (for +26D). As expected, the two measured so called 'aberration corrected' IOL showed a SR of about 40% less then the best measured standard lenses. This is due to the fact that the ISO measurement setup does not account for eccentricity of the natural cornea which is supposed to be compensated by these lenses and hence results in inferior measurement results. Nevertheless all of the measured foldable IOL reached their original optical imaging quality after a period of up to 30 minutes after the Insertion.

The injection process itself obviously does not permanently influence the optical imaging quality of the analyzed IOL. However the imaging quality decreases of up to 70% over a period of up to 20 Minutes after the injection. After a period of 30 minutes all IOL unfolded autonomous to their original geometry and hence reached their original imaging quality. Due to the future continuous decrease of the incision size and hence the decreasing diameter of the cartridges used, it has to be ensured that the optical properties of the IOL are not influenced by the injection process and the used cartridges.