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The results show that toric IOL implantation can help an estimated 20% of patients with astigmatism achieve good vision and a reduced need for distance spectacles. If IOL rotation occurs, it is usually during the first week and can be remedied by repositioning the IOL at 1 week.

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Many types of prisms have been designed for use in various optical instrument applications. Most have unique shapes as demanded by the geometry of the ray paths, reflection and refraction requirements, and compatibility with manufacture, weight reduction considerations, and provisions for mounting. Before we consider how to mount these prisms, we should understand how they are designed. Our first topics in this chapter are the functions of prisms, geometric relationships that govern those functions, refractive effects, total internal reflection, and the construction and use of tunnel diagrams. We then see how to determine aperture requirements and reference analytical means for calculating thirdorder aberration contributions from prisms. The chapter closes with design information for 30 types of individual prisms and prism combinations frequently encountered in optical instrument design.