Abstract
Purpose :
Poly(methyl methacrylate) (PMMA) three-piece intraocular lenses (IOLs) have poor durability for manipulation, resulting in haptic fracture or permanent bending. This study evaluates the mechanical properties of PMMA IOL haptics through stress-strain analysis and bend testing before and after applying heat to the material to enhance the durability and flexibility.
Methods :
PMMA haptic material is heat treated by a water bath, for clinical relevance, at 8 different temperatures, and mechanically tested in tension, compression, and bending procedures. This method is then applied to 20, three-piece intraocular lenses, of the same manufacture.
Results :
Preliminary data from this study indicates that after heat was applied to the PMMA haptics, the Young’s Modulus was decreased by approximately 10%, and the average load force was decreased by approximately 25%. Experimental results show that at bending angles of 75 degrees and more acute, there is progressive deformation of the PMMA haptics at room temperature. Heating the haptics from 40°C to 45°C, for five minutes, showed minimal deformation immediately after bending that resolved after 20 minutes. Heating the haptics at any temperature above 35°C for 10 minutes led to increased deformation, when compared to five minutes, that did not resolve after 20 minutes. When heated from 50°C to 55°C, the haptic deformation improved, but did not completely resolve after 20 minutes. When heated past 60°C for five minutes, the haptic material undergoes permanent plastic deformation before performing the bending procedures. The data collected from experimental bending procedures showed a trend that the PMMA haptic material did not permanently deform when heated for five minutes between 40-45° C. When heated past 50°C for five minutes, the haptic material undergoes permanent plastic deformation with loss of elastic memory after bending procedures.
Conclusions :
Pre-heating of PMMA IOLs within particular temperature ranges decreases their stiffness, enhances their flexibility, and reduces capacity for permanent plastic deformation. Such treatments may allow increased use of conventional PMMA IOLs for surgeries where haptic manipulation is expected (i.e. scleral fixation) by reducing the risk of plastic deformation due to haptic bending.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.