Effect of astigmatism on multifocal intraocular lenses

Purpose: To study the effect of astigmatism on multifocal intraocular lens (MIOL) function, Setting: Laser Laboratory, Department of Electronics, Electrotechnics and I nformatics, University of Trieste, Italy. Methods: Using an experimental optical system, this study compared the divi sion of a laser beam in the focal spots of 1 monofocal IOL (Pharmacia 722A) , 1 bifocal IOL (Pharmacia 811E), and 2 MIOLs (AMO Array MPC25NB and Domile ns Progress 1). The model consists of a helium-neon laser and an optical sy stem: a triangular optical bench with a precision collimator, a micropositi onable immersion stage to support the IOL, and a digital image-processing s ystem. Astigmatism was induced by interposing a +1.0 diopter (D) cylinder l ens between the IOL and the television camera. Astigmatism was corrected by adding a -1.0 D cylinder lens in front of the IOL on the same axis. Results: Astigmatism creates pairs of focal lines, 1 for each focal spot in the IOL. In the multifocal IOL, the posterior focal line of the nearest fo cus interfered with the anterior line of the next focus. Correcting the ast igmatism led to a significant reduction (mean 20%) in light intensity. Conclusions: Astigmatically neutral surgery or surgical correction of pre-e xisting astigmatism is essential in MIOL implantation to minimize the decre ase in contrast sensitivity. J Cataract Refract Surg 1999; 25:804-807 (C) 1 999 ASCRS and ESCRS.