Comparison Of Lens Surface Geometry Using Optical Coherence Tomography And Scanning Electron Microscopy

The optical properties of an Intraocular lens (IOL) can be determined by its surface geometry, thickness, and material. Assessment of surface geometry is challenging given the resolution that is required to accurately assess subtle lens details that govern the performance of modern IOLs.

The study was conducted at the Cataract and Refractive Surgery Laboratory and Electron Microscopy Unit, University of Plymouth, United Kingdom.

Assessment of surface geometry was conducted on: A sperical IOL (CT Spheris 209M), aberration-neutral IOL (CT ASPHINA® 409M), aberration-correcting IOL (CT ASPHINA 509), and an aberration-correcting IOL that has a unique surface profile designed to make it robust to decentration (CT LUCIA). A Ganymede™ Series SD-OCT with an OCT-LK4-BB scanning lens and immersion kit (Thorlabs) was used to acquire images of the IOL surfaces while immersed. Both sides were scanned separately. Following this, a ZEISS Crossbeam 550 focused ion beam-scanning electron microscope (FIB-SEM) was also used to acquire surface images for analysis. Image analysis was conducted in Matlab to determine the radius of curvature and lens asphericity.

Both methods were able to determine the progressive flattening between the spherical, aberration-neutral, and then aberration-correcting IOLs. The CT Lucia provides an interesting profile that flattens before steepening again into the periphery. This more complex shape was identifiable through SEM, but the resolution of the OCT limited the assessment of this geometry.

Assessment of surface geometry is difficult; OCT is able to differentiate simple surface geometry, but higher resolution is required for complex surface designs.