Conventional PMMA intraocular lenses (IOLs) have been shown to restore vision successfully after cataract surgery, but have been associated with complications such as decentration, destruction of intraocular tissue, and posterior capsule opacification. Expansile IOLs based on cross-inked polyhydroxyethylmethacrylate (PHEMA) also undergo chemically induced hydrolysis, polymer leaching and gel fragmentation. The focus of this research is to prepare and characterize hydrogel IOLs prepared from PVP using gamma-irradiation.
Methods: Hydrogels were prepared from aqueous solutions of PVP by free radical polymerization as a function of gamma-irradiation dose (0.5 x 106 to 2.5 x 106 rad), PVP concentration (4% to 16% w/v), molecular weight (MW) (10 x 103 to 360 x 103 Da), and blending with low and high MW PVP. Viscometric analysis, swelling characterization studies, and polymer leaching studies were carried out to access network formation. In addition changes in lens geometry in an animal model were measured in response to cycloplegic eyedrops.
Results: Cross-linking efficiency was greatest with an initial MW of 360 x 103 Da and lowest with an initial MW of 10 x 103 Da. The time to reach equilibrium from the glassy state and the degree of swelling in saline decreased with increasing gamma-irradiation dose and increased with concentration of PVP and blending of low and high MW PVP. The equilibrium water content ranged from 90 to 98% (w/w). Eighty-five percent of the equilibrium dimensions could be achieved within 90 min. Gravimetric analysis and HPLC indicate that the amount of PVP that is not incorporated into the network ranges from 0.25% to 6% (w/w). This was inversely related to the gamma-irradiation dose. The MW of the leached samples was estimated to be greater than 10 x 103 Da in all cases.
Conclusions: PVP hydrogel IOLs prepared by gamma-irradiation have advantages in terms of chemical stability, high water content, and ease of preparation. They may not need further purification or sterilization prior to implantation. In addition, they may allow for accommodation. No comments can be made regarding the biocompatibility, long-term stability, or optical quality at this time.