CHANGES IN REFRACTION INDUCED BY CHANGE IN INTRAOCULAR-LENS POSITION

BACKGROUND: Intraocular lens (IOL) decentration and tilt may affect po stoperative refractive errors through spherical aberration of the IOL. METHODS: Through a use of a ray-tracing program and by minimizing alg orithm, we calculated theoretical refractive errors for various degree s of IOL decentration and tilt. We compared our results with those obt ained by paraxial vergence calculations. RESULTS: IOL decentration and /or tilt shifted postoperative refractive errors toward myopia and ast igmatism of oblique origin. For example, a 3-millimeter decentration o f an IOL resulted in induction of approximately - 2.00 diopters (D) sp here and +0.70 D cylinder. IOL tilt affected refractive errors to a le sser degree. The change in refractive error caused by a combination of IOL decentration and tilt depended on the relationship between the ge ometrical axes of decentration and tilt. In the case of the least favo rable combination of 12-degrees of tilt and 3 mm of decentration, it c an reach -7.00 D sphere and +4.00 D cylinder. CONCLUSIONS: IOL decentr ation and/or tilt increase myopia and astigmastism. They are negligibl e for small decentrations, but could be sources of substantial postope rative refractive errors if the decentration or tilt is large.