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T. M. Eppig, A. Langenbucher; Effect of Decentration and Tilt on the Image Quality With Toric Intraocular Lenses. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5612.
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To investigate the impact of decentration and tilt on the monochromatic modulation transfer function (MTF) with different toric intraocular lenses within a schematic model eye and to investigate the difference between monotoric, bitoric and aspheric lens designs.
The Liou-Brennan Model Eye was used as basis for the simulations. The anterior corneal shape was modified to simulate a considerable amount of corneal astigmatism (4 D). The crystalline lens was replaced by several artificial toric intraocular lens design concepts which were derived from real intraocular lens data. One standard spherical monotoric, one aspheric monotoric (aberration neutral) and one aspheric bitoric (aberration neutral) intraocular lens design were chosen for simulation. The predesigned lenses were placed at a fixed axial position within the eye and the focal plane was optimized using a minimum RMS optical path difference criterion for 3.0 mm iris pupil diameter. The lenses were then decentered relative to the pupil center up to 1.00 mm (temporally and nasally) in the 0° (steep) meridian and the 45° meridian. In a second step the lenses were tilted in the mentioned meridians relative to the line of sight. The monochromatic MTF was calculated for each position for 3.0 and 4.5 mm iris pupil diameters.
All designs showed significant dependence to decentration. Tilt had only minor effect on the image quality. The aspheric toric lens designs (monotoric & bitoric) showed an overall superior optical performance compared to the standard toric lens and were more robust to decentration and tilt. Results depended slightly on the direction of the cylinder axis relative to the misalignment. Degradation of image quality in presence of misalignment was more prominent with the 4.5 mm pupil than with the 3.0 mm pupil. Monotoric and bitoric designs showed comparable image quality.
Aspherizing toric intraocular lenses is a good approach for providing better image quality in pseudophakic eyes with considerable corneal astigmatism. However, proper alignment is important for maintaining the benefits of toric intraocular lenses. No major advantage of the bitoric design in comparison with the monotoric aspheric design was found.
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