PubMed · 714383
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A Y Anis. 1978. Lens loop forceps.. https://doi.org/10.1016/s0161-6420(78)35607-4
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Since understanding the mechanical properties of intraocular lens (IOL) haptic materials can minimize decentration after surgery, we have examined shape recovery ratios of various intraocular lens haptics (polypropylene [PP], polyvinylidene fluoride [PVDF], extruded poly(methyl methacrylate) [PMMA]) currently on the market under conditions that approximate clinical use. The results using various Ascon lens-holding forceps and compression tests, during which the lenses were held in a cylindrical holder for seven days, one month, and three months, indicated that PVDF haptics had better shape recovery capability than PP and extruded three-piece PMMA haptics.
A model eye water cell was used to evaluate the optical performance of biconvex, meniscus, and plano-convex (spheric and aspheric) monofocal poly(methyl methacrylate) intraocular lenses when the lenses were centered and when they were decentered 1 mm and 2 mm. Resolution, induced astigmatism, and modulation transfer function measurements were performed for all lenses with the more convex surface of the lens oriented toward the incident light. The same measurements were performed for the plano-convex and meniscus lenses in the reverse orientation. The lens shapes least affected by decentration were the biconvex and spheric plano-convex with the convex surface oriented toward the incident light. When centered, the aspheric plano-convex lenses had the best overall contrast performance based on the modulation transfer function measurements. However, once decentered the performance of the aspheric lenses approached that of the meniscus lenses in the reverse orientation, the lens shape which had the worst performance.
Birefringent lenses provide two simultaneous powers. One power is provided by ordinary rays, the other by extraordinary rays through the lens. Because the difference between the reading and distance powers of intraocular lenses is small when compared to the average lens power, the difference between the extraordinary and the ordinary index of refraction of birefringent intraocular lenses can also be small. It is shown that a single birefringent intraocular lens which is manufactured from a properly oriented polymeric lens material provides the two powers needed for distant viewing and reading. Compound lenses consisting of M birefringent lens components provide up to 2M powers within a desired interval. Degrees of freedom exist for the choice of power values inside the desired interval and for the intensities associated with the individual powers.