The posterior capsular opacification (PCO) represents the most significant cause of visual impairment after cataract surgery. During the last decade, a great deal of work has been conducted to analyze which intraocular lens (IOL) property could primarily influence the rate and severity of PCO. It was found that the geometrical design of IOL affects the rate of PCO and it has been proven that a sharp IOL posterior optic edge improves the prevention of PCO. On the other hand, the surface properties of the IOL biomaterial also appeared to play a relevant role in preventing PCO. In this work we investigate, with nanometer scale resolution, the physical properties of the surface for the IOL biomaterials currently in use in the clinical environment: polymethyl-methacrylate (PMMA), silicone, hydrophilic acrylic and hydrophobic acrylic. An Atomic Force Microscope was used both to measure the topography and adhesiveness of IOLs' optic surface. Analysis of IOLs was performed in liquid environment. The topography measurements of the IOLs' optic were performed using an Autoprobe CP (Veeco, Sunnyvale, CA) operated in the contact mode and V-shaped cantilevers with a 0.01 Newton/meter (N/m) nominal elastic constant. The topography of IOLs' surface revealed different features strongly correlated with both the lens biomaterial and the processes used to manufacture the IOLs. The root mean square (RMS) roughness of the IOL optic surface was significantly different between lenses of various materials (P < 0.001): hydrophobic acrylic and silicone IOLs have shown the lowest surface roughness, i.e., 3.8 +/- 0.2 nanometer (nm) and 4.0 +/- 0.5 nm respectively, whereas the highest surface roughness (7.0 +/- 0.6 nm) was measured for PMMA lenses. The mean RMS roughness of the hydrophilic acrylic lens was 5.0 +/- 0.5 nm. The adhesive properties of IOLs' surface was studied using a NanoScope III (Veeco, Sunnyvale, CA), operated in the Force-vs-Distance (f-d) mode with rectangular cantilevers of nominal elastic constant of 10 N/m. A statistically significant correlation between adhesion properties of each IOL and their constituent material was measured (P<0.001). The hydrophobic acrylic IOL exhibited the largest mean value for the adhesive force (283.75 +/- 0.14 nanoNewton, nN) followed by the hydrophilic acrylic (84.76 +/- 0.94 nN), PMMA (45.77 +/- 0.47 nN) and silicone IOLs (2.10 +/- 0.01 nN). AFM was demonstrated to be an effective and accurate tool for the analysis of the IOL's optic. The surface properties of the biomaterials used to manufacture IOLs are important factors as they can influence the incidence and severity of PCO. While further studies are necessary to elucidate the mechanism of PCO development and the interface interactions between the IOL and capsule, the results from this work may enhance the theory of manufacturing materials with smooth and adhesive optic surface to prevent PCO.
INTRAOCULAR LENS SURFACE PROPERTIES INVESTIGATED WITH NANOMETER SCALE RESOLUTION USING ATOMIC FORCE MICROSCOPY
De Santo MP;BARBERI, Riccardo Cristoforo
2009-01-01
Abstract
The posterior capsular opacification (PCO) represents the most significant cause of visual impairment after cataract surgery. During the last decade, a great deal of work has been conducted to analyze which intraocular lens (IOL) property could primarily influence the rate and severity of PCO. It was found that the geometrical design of IOL affects the rate of PCO and it has been proven that a sharp IOL posterior optic edge improves the prevention of PCO. On the other hand, the surface properties of the IOL biomaterial also appeared to play a relevant role in preventing PCO. In this work we investigate, with nanometer scale resolution, the physical properties of the surface for the IOL biomaterials currently in use in the clinical environment: polymethyl-methacrylate (PMMA), silicone, hydrophilic acrylic and hydrophobic acrylic. An Atomic Force Microscope was used both to measure the topography and adhesiveness of IOLs' optic surface. Analysis of IOLs was performed in liquid environment. The topography measurements of the IOLs' optic were performed using an Autoprobe CP (Veeco, Sunnyvale, CA) operated in the contact mode and V-shaped cantilevers with a 0.01 Newton/meter (N/m) nominal elastic constant. The topography of IOLs' surface revealed different features strongly correlated with both the lens biomaterial and the processes used to manufacture the IOLs. The root mean square (RMS) roughness of the IOL optic surface was significantly different between lenses of various materials (P < 0.001): hydrophobic acrylic and silicone IOLs have shown the lowest surface roughness, i.e., 3.8 +/- 0.2 nanometer (nm) and 4.0 +/- 0.5 nm respectively, whereas the highest surface roughness (7.0 +/- 0.6 nm) was measured for PMMA lenses. The mean RMS roughness of the hydrophilic acrylic lens was 5.0 +/- 0.5 nm. The adhesive properties of IOLs' surface was studied using a NanoScope III (Veeco, Sunnyvale, CA), operated in the Force-vs-Distance (f-d) mode with rectangular cantilevers of nominal elastic constant of 10 N/m. A statistically significant correlation between adhesion properties of each IOL and their constituent material was measured (P<0.001). The hydrophobic acrylic IOL exhibited the largest mean value for the adhesive force (283.75 +/- 0.14 nanoNewton, nN) followed by the hydrophilic acrylic (84.76 +/- 0.94 nN), PMMA (45.77 +/- 0.47 nN) and silicone IOLs (2.10 +/- 0.01 nN). AFM was demonstrated to be an effective and accurate tool for the analysis of the IOL's optic. The surface properties of the biomaterials used to manufacture IOLs are important factors as they can influence the incidence and severity of PCO. While further studies are necessary to elucidate the mechanism of PCO development and the interface interactions between the IOL and capsule, the results from this work may enhance the theory of manufacturing materials with smooth and adhesive optic surface to prevent PCO.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
