Noncontact profiling techniques for intraocular lens edge measurements

Two techniques, focal spot projection and fringe projection, have been developed for profiling the edges of anterior-chamber style intraocular lenses (IOL). The techniques are based on measurement of the trajectory of reflected light when an incident beam is focused and stepped across the edge surface (spot projection) or when two focused beams combine to form an optical interference pattern on the edge (fringe projection). The optical configurations for performing the projection techniques are described along with the mathematical relationship between the reflected-beam trajectories and the edge profile. An automated system for the implementation of focal spot projection was developed. The system has the capability of positioning the IOL edge at the focal point of the incident beam, acquiring trajectory data via stepper motors and a TV camera, processing the data to generate a profile, and displaying the profile on the computer video monitor or in hard-copy form via a printer. On one lens tested, three profiles corresponding to different locations along the IOL edge could be generated without user intervention. However, the user has the option of manually positioning the IOL to permit greater versatility. The typical 300-microm wide IOL edges are profiled to a resolution of approximately 20 microm. To constrain optical and microprocessor hardware costs, compromises were made in operating speeds so that approximately 20 min is required per profile. With current trends in integrated circuit technology future generations of the system could be made faster and prove useful as a QC tool for the IOL industry. Furthermore, the present device can be used in determining appropriate IOL profile standards.