Abstract <p>An experimental study was conducted on optimal modes for local optical property modification of polymethyl methacrylate (PMMA) and hydrophobic acrylic using focused (NA = 0.25) femtosecond laser pulses in the near-IR range (wavelengths of 1030 nm and 1557 nm). Modified regions measuring 3 to 10 μm in width and 30 to 200 μm in depth were obtained within the peak intensity range of 2.5–50 TW/cm², with a controlled variation in refractive index ranging from 1 × 10^–4 to 1 × 10^–3. These regions are also characterized by increased intensity of Raman bands around 1350–1400 cm⁻¹ in hydrophobic acrylic and 1610–1670 cm⁻¹ in PMMA, which may be attributed to polymer chain scissions. The identified patterns suggest a similarity in the laser-induced changes and confirm the possibility of writing optically transparent phase elements in the volume of these materials. The method applied in this study shows promise in ophthalmology for creating individual refractive index profiles and postoperative correction of the optical power of intraocular lenses. Additionally, it has potential for manufacturing diffractive and integral micro-optical elements from biocompatible polymers.</p>