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Pablo De Gracia; Stability of multifocal lenses in subjects with residual astigmatism, coma, and spherical aberration. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):6113.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate the effects of normal residual values of astigmatism after proper prescription and normal values of coma over the optical performance of multifocal lenses. This study compares the performance and the stability against the effects of coma, spherical aberration (SA), and astigmatism of various design philosophies.
A computer model was developed to test the interaction of bifocal (2 and 4 zones) and trifocal designs (3 and 6 zones) with astigmatic values ranging from 0 to 1 D, of coma ranging from 0 to 1 µm, and of spherical aberration ranging from 0 to 1 µm. The optical performance was evaluated by calculating the through focus values of an optical quality metric (VSOTF) for angular (slices of a pizza) and radial (concentric circles) designs. The area under the curve; the change introduced by coma, SA, and astigmatism in the original VSOTF of the different designs; and the range above threshold are used as the indexes to evaluate the optical performance of such interactions. Computations are repeated for pupil diameters of 3, 4, 5, and 6 mm.
Designs with a higher number of zones (4 and 6 zones) are more stable against the effects of astigmatism and coma. Normal residual values of astigmatism of 0.5 D distort on average a 10% the initial profile. A strong interaction between the direction of coma and bifocal 2 angular designs has been found. Optical performance of angular designs is superior to that provided by radial designs. Radial designs are, because of their marked differences in geometry with the two aberrations studied, more stable against coma and astigmatism than angular designs.
When prescribing multifocal prescriptions, astigmatism should be corrected to the lowest value possible. In the cases in which coma and residual astigmatism are significant, designs with a higher number of areas will provide a more predictable optical performance across subjects. Although designs with angular divisions provide a better optical performance, their interactions with residual astigmatism and natural coma is stronger than the one occurring with radial divisions. SA does not show any strong interaction with radial or angular designs.
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