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A. Ho, F. Manns, J. Ale, Y. Lee, J.-M. Parel; Depth of Focus of Accommodating Intra-Ocular Lenses: A Paraxial Analysis. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1797.
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To investigate the performance of one-lens (1LAIOL) and two-lens (2LAIOL) accommodating intraocular lenses in terms of depth of focus (DoF).
A paraxial eye model, modified from the Navarro eye and adjusted for paraxial focus, was used. To simulate the effect of AIOL implantation, the surfaces representing the crystalline lens were replaced with one or two thin lenses. For reference, DoF of the ‘natural’ eye (with the original crystalline lens surfaces) was calculated. A 20 µm blur circle size limit was assumed throughout; giving a total DoF for the natural eye of 0.53D (4 mm pupil).We studied the effect of AIOL position on DoF by varying the distance focus position of the AIOL from 1 mm to 3 mm behind the iris. We also studied the effect of 2LAIOL front/back lens power combinations on DoF by varying front lens power from 25D to 40D in 5D steps. In all cases, lens power (1LAIOL) or back lens power (2LAIOL) was selected to maintain distance focus.For each scenario, we studied the effect of near focus (up to 1 mm translation) on DoF. We analysed two 2LAIOL cases; front lens translating forward, and back lens translating backwards.Total DoF was defined as the limits of vergence in object space that produce the 20 µm blur circle size.
At distance focus, all AIOL had greater DoF (range=0.514D to 0.535D) than the reference eye. Moving the position of all AIOL posteriorly (with a higher lens power to maintain focus) increases DoF by 8.5mD (milli-dioptres) per mm of position change. DoF of all AIOL decreases when focused for near; 1LAIOL fared worst (DoF decreasing 2.2mD per D of near focus), while DoF of 2LAIOL decreases from between 1.7 to 0.4mD per D of near focus.For 2LAIOL, DoF increases by 0.04mD per D of front lens power increase. Back lens translating 2LAIOL show virtually no change in DoF with change in lens power; and suffers the least DoF decrease with near focus. At distance focus setting, DoF of 2LAIOL is independent of lens power.We emphasise that all effects on DoF are minute, changing by less than 0.01D in all cases. This is far smaller than the precision of any measurements of DoF.
Within practical limits, lens power and position of implantation of AIOL have negligible effect on DoF.
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