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Phillip Gooding; Geometric Limitations of Indexing Toric IOL designs Utilizing FS Laser Asymmetric Capsulotomy. Invest. Ophthalmol. Vis. Sci. 2016;57(12):1316.
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© ARVO (1962-2015); The Authors (2016-present)
One of the unique capabilities of laser assisted cataract surgery is the ability to create a precise non-circular capsulotomy. This asymmetric feature could potentially be used to precisely locate an IOL with matching asymmetric engagement both laterally and rotationally. The primary motivation for this capability is to assure accurate orientation and stability of toric IOLs. Sensitivity of rotational orientation of aspheric IOLs is well known. The analysis in literature shows a complete loss of cylinder correction with a 30 degree placement error.
Several asymmetric geometries were selected as candidates for capsular bag rotational indexing and evaluated against the criteria of maximizing the asymmetry aspect ratio to create the strongest indexing potential, maximizing the IOL clear aperture, and staying within the capsular area available for laser cutting through the dilated pupil.Data from over 19,000 CATALYS procedures were analyzed to determine the maximum available capsulotomy diameter accounting for capsulotomy position with respect to pupil diameter and position.Capsular strain was estimated for two existing capsulotomy mounted IOL designs and compared with potential asymmetric IOL designs that maintain a minimum 5mm clear aperture.A literature search was performed to establish realistic limits on allowable capsule strain during and after IOL installation.
Figure 1 shows the allowable major axis iris dimension as a function of frequency. A capsulotomy of 5mm or less can be performed in 90% of cases.Capsulotomy perimeter strain for the Morcher bag-in-lens IOL and Femtosecond IOL was estimated to be as high as 25%. Strain was estimated for several candidate asymmetric geometries for comparison.Literature indicates that greater than a 30% capsular strain could potentially be problematic indicating that the strain induced by designs currently in use may be the permissible limit.Figure 2 shows a comparison of the estimated strain of existing designs compared with potential asymmetric designs.
Due to the limitation of pupil diameter and capsulotomy placement during femtosecond laser capsulotomy creation of an asymmetric opening with an aspect ratio that may be useful for rotational stability cannot be created without either inducing excessive strain on the capsule or requiring less than a 5mm IOL clear aperture.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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