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  • Title: Some factors governing the efficacy of positional pseudoaccommodative intraocular lenses.
    Author: Alió JL, Patel S.
    Journal: Ophthalmology; 2005 Nov; 112(11):2009-14. PubMed ID: 16183130.
    Abstract:
    PURPOSE: To examine the effects of ametropia (spherocylindrical), corneal curvature, target anterior chamber depth (ACD), misplacement, and some design features on the performance of positional pseudoaccommodative intraocular lenses (PPAIOLs). DESIGN: Theoretical investigation based on computer models to determine the practical limitations of PPAIOLs. METHODS: Using a suitable model eye featuring gradient index optics within the cornea, the PPAIOL curvatures were calculated for axial ametropia ranging from -10 diopters (D) to +10 D, where the IOL was located at an ACD of 4.05 mm. The change in refraction (y) of the hypothetical pseudophakic eye was calculated for each millimeter of forward movement (x) of the PPAIOL up to 1 mm from the pole of the corneal back surface. The computations were repeated for a range of hypothetical PPAIOL refractive indices (1.49-1.70), ACDs, equiconvex and meniscus (back surface radius, -10 mm and -25 mm), corneal astigmatism (-1 D to -5 D), and radii (after corneal refractive surgery). MAIN OUTCOME MEASURES: Diopter/millimeter values represent the gradient of the relationship between x and y. Mathematical models describe the association between the diopter/millimeter gradient and key clinical dependent variables. RESULTS: (1) For a polymethyl methacrylate (refractive index, 1.49) PPAIOL of equiconvex design and 4.05-mm ACD, the predicted diopter/millimeter value is a function of ametropia (a), where diopter/millimeter = 1.666+0.136a+0.0018a2. (2) For 6-mm ACD and a refractive index of 1.7, diopter/millimeter = 1.836+0.159a+0.0027a2. (3) The equiconvex design benefits hyperopic but not myopic eyes. (4) For PPAIOLs correcting >4 D of astigmatism, more than 0.5 D of residual astigmatism is present at near after 1 mm of IOL displacement. (5) In emmetropic cases, the predicted diopter/millimeter value is a function of the corneal radius (r) where diopter/millimeter = 7.376-1.162r+0.0545r2. (6) Positional pseudoaccommodative IOL misplacement does not significantly affect the accommodative ability. CONCLUSIONS: (1) Hyperopic eyes with relatively steep corneas should benefit more from the PPAIOL than myopic eyes with relatively flat corneas. (2) A full, binocular, near refraction should be performed to correct any residual spheroastigmatism in anisometropia and cases in which the PPAIOL is toric.
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