Comparison of poly (methyl methacrylate) and acrylic hydrophobic intraocular lens surface irregularities using atomic force microscopy

Background: Posterior capsule opacification (PCO) is a very frequent complication of phacoemulsification surgery in patients undergoing cataract extraction. This has led to modifications in design and material of intraocular lenses (IOLs). There is increasing evidence suggesting that foldable acrylic hydrophobic IOLs are associated with lower PCO incidence. However, traditional rigid poly methyl methacrylate (PMMA) IOLs are still in widespread use due to the large number of manual small-incision cataract surgeries performed in developing countries. The amount of surface irregularities on an IOL is linearly correlated to the rate of lens epithelial cell (LEC) migration and hence to the occurrence of PCO. Objective: Surface roughness parameters of PMMA and acrylic hydrophobic IOLs were compared using atomic force microscopy (AFM). Topological characteristics of 7 PMMA and 4 acrylic hydrophobic IOLs obtained from various manufacturers were evaluated with AFM in tapping mode. A V-shaped, silicon nitride cantilever with a tip curvature <10 nm, length 115135 μm and a spring constant in the range of 0.20-80 N/m was used. All images were acquired with a resolution of 256×256 data points per scan at a scan rate of 0.5 Hz per line and a scan size of 10×10 μm. Results: AFM images of IOL optic surfaces showed a collection of pores, grooves, ridges, very small peaks and surface irregularities. Acrylic hydrophobic IOLs showed significantly less surface roughness when compared with PMMA IOLs. Conclusions: AFM is a powerful technique for topological characterization of IOLs. Acrylic hydrophobic IOLs appear to be more suitable in preventing PCO compared with PMMA.