Quality of images with toric intraocular lenses

Purpose: To objectively evaluate the image quality obtained with toric intraocular lenses (IOLs) when misaligned from the intended axis. Setting: University Eye Clinic and the Department of Industrial and Information Engineering, University of Trieste, Trieste, Italy. Design: Experimental study. Methods: An experimental optoelectronic test bench was created. It consisted of a high-resolution monitor to project target images and an artificial eye. The system simulates the optical and geometric characteristics of the human eye with an implanted toric IOL. A 3.00 diopters corneal astigmatism was simulated. Images reproduced by the optical system were captured according to different IOL axis positions. The quality of each image was analyzed using the visual information fidelity (VIF) criterion. The VIF reduction was calculated at each IOL rotational step. Results: A 5-degree IOL axis rotation from the intended position determined a decay in the image quality of 7.03%. Ten degrees of IOL rotation caused an 11.09% decay of relative VIF value. For a 30-degree rotation, the VIF decay value was 45.85%. Finally, the image decay with no toric correction was 56.70%. Conclusions: The more the objective quality of the image decays progressively, the further the axis of the IOL is rotated from its intended position. The reduction in image quality obtained after 30 degrees of toric IOL rotation was less than 50% and after 45 degrees, the image quality was the same as that of no toric correction

Refractive surprise after toric intraocular lens implantation: Graph analysis

PURPOSE: To determine the refractive cylinder effect of rotating a toric intraocular lens (IOL) and identify the sources of refractive astigmatic surprise after toric IOL implantation. SETTING: Private practice, Melbourne, Australia. DESIGN: Experimental study. METHODS: Vergence formulas using a standard reduced eye model were used to bring all lens powers to the corneal plane. Double-angle vector diagrams were then used to (1) determine the refractive cylinder effect of rotating a toric IOL and (2) show how the prevailing astigmatism and the various planning and surgical steps involved in implanting a toric IOL contribute to the postoperative manifest refractive cylinder. RESULTS: An example calculation is given to illustrate the method. CONCLUSIONS: Refractive cylinder surprises can occur after toric IOL implantation. Understanding the causes enables surgeons to address contributory factors and choose an appropriate surgical method for managing individual cases of refractive cylinder surprise. Financial Disclosure: Dr. Alpins and Mr. Stamatelatos have a financial interest in the Assort software program used to support the planning and analysis of astigmatic correction. Dr. Ong is an employee of Assort