# Laser Processing of Intraocular Lenses
## 3 Results
### Characterization of Structural Modification and Chemical Composition  
Following laser irradiation, the primary goal was to confirm that the physical and chemical properties of the IOLs are retained unaltered or at an acceptable degree, ensuring their suitability for ophthalmological use in patients. To verify this, micro-Raman measurements were conducted using the Ar\({}^{+}\) 514.5 nm line for excitation. Care was taken to keep the laser power at a low level, to avoid laser-induced modifications: ca. 275 \(\mu\)W for the \(\times\)20 lens and 45 \(\mu\)W for the \(\times\)100 lens. Both regular and confocal micro-Raman spectra were acquired in the wavenumber region 100-3200 cm\({}^{-1}\). For the measurements with the \(\times\)20 lens, each spectrum corresponds to an acquisition time of 40 s for both IOLs, preceded by a bleaching time of 120 s: the reason for quenching the photoluminescence was to have an easier way to compare the Raman spectra of the polymer in the pristine and the laser-irradiated PMMA samples and thus detect possible irradiation-induced polymer modifications. To increase the possibility of probing a thinner surface layer of the sample, where the laser irradiation is expected to be maximal, with reduced interference from less irradiated areas lying deeper below the surface, we ran confocal measurements with the \(\times\)100 lens: the acquisition time was set at 40 s for PMMA IOLs and 120 s for acrylic IOLs without bleaching, so as to have a direct way to compare with results from the literature. Raman spectra of the PMMA IOL before and after laser ablation with femtosecond 1064 nm and CW 405 nm are illustrated in Figure 11. The Raman spectra exhibit sharp peaks and broad bands, consistent with those reported in the literature [34; 35; 36]. Among the observed eight strongest Raman bands, the most prominent one is at 2951 cm\({}^{-1}\). This is assigned to the overlap of the symmetric C-H stretching vibration of O-CH\({}_{3}\) (methyl group forming part of the ether C-O-C chain) with the asymmetric C-H stretching vibration of \(\alpha\)-CH\({}_{3}\) (methyl group attached to a backbone C) [35]. The corresponding symmetric  
Figure 10: An optical microscope image of the ablated line created on the PMMA lens with the CW 405 nm laser. C-H stretching vibration of \(\alpha\)-CH\({}_{3}\) is the shoulder seen at ca. 2885 cm\({}^{-1}\) (discernible only after sufficient magnification in the figure). The band at 3000 cm\({}^{-1}\) is the asymmetric C-H stretching vibration of O-CH\({}_{3}\). The 2843 cm\({}^{-1}\) is assigned to the CH\({}_{2}\) (methylene) symmetric C-H stretch; the CH\({}_{2}\) asymmetric C-H stretch is a shoulder at ca. 2935 cm\({}^{-1}\) (not discernible in the figure). The band at 1450 cm\({}^{-1}\) is the O-CH\({}_{3}\) symmetric bending vibration, while other-type methylene or methyl bending vibrations are seen at lower intensity in the vicinity, as shoulders or broader bands. The C=O stretch is observed at 1725 cm\({}^{-1}\), the C-O-C symmetric stretch appears at ca. 813 cm\({}^{-1}\), while the symmetric C-C-O (the central C is the one with the carboxyl bond) stretch is observed at 600 cm\({}^{-1}\)[34]. The symmetric CH\({}_{3}\) rocking modes form the doublet at 967 (\(\alpha\)-CH\({}_{3}\)) and 989 cm\({}^{-1}\) (O-CH\({}_{3}\)). In Figure 12, we present Raman spectra of the acrylic IOL before and after laser ablation with femtosecond 1064 nm and CW 405 nm. The pristine IOL Raman spectrum is very similar to the Alcon (Acrysof) model MA60 BM IOL hydrophobic acrylic material (Alcon, Forth Worth, TX, USA) shown in [37] or to the hydrophobic UV-photo-reactive polybenzylmethacrylate polymer (produced by Contaetq, Eindhoven, The Netherlands) shown in [23] or even the copolymer-based Hydrophobic Foldable Ocular (HPO) material (produced by Soleko s.p.a.) reported in [38].