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Femtosecond laser micromachining in hydrophobic intraocular lenses: efficacy and material effects

Intraocular lenses (IOLs) are widely used to treat cataracts and restore vision, however, the accuracy of manufacture and surgical implantation of IOLs is subject to some limitations. Femtosecond laser micromachining relies on tightly focused, ultrashort laser pulses to locally modify the properties of bulk materials, and has been recently applied in the field of vision correction. In this study, multi-layer dense line patterns were inscribed into Tecnis IOLs using a femtosecond laser operating at 8.3 MHz at a wavelength of 405 nm. Below the damage threshold, uniform phase changes could be obtained within each pattern, and its magnitude increased nonlinearly with laser power. To explore the mechanisms underlying the refractive index (RI) changes, microstructural changes of the phase pattern were quantified by confocal micro-Raman spectroscopy using sectioned IOLs. A significant decrease of the integral intensity of 2988 cm-1 band (v(C-H)) that confined in the written layer was observed from the lateral scan profile of IOL cross section. We posit that the positive RI changes in IOLs were likely associated with localized photochemical depolymerization, which includes broken of chemical bonds and diffusion of molecular fragments. These findings enhance our understanding of femtosecond micromachining as a new method to customize high visual-quality IOLs.