Limitations of correcting spherical aberration with aspheric intraocular lenses.

PURPOSE

Aspheric intraocular lenses (IOLs) are deigned to correct spherical aberration in pseudophakic eyes. We predict the benefit from correcting spherical aberration based on simulations and aberrometry of pseudophakic eyes implanted with spherical IOLs.

METHODS

Ray tracing was performed through a model eye with an equi-biconvex spherical IOL and with a spherical aberration-correcting aspheric IOL. The IOLs were increasingly tilted and/or displaced, and the resulting transverse aberrations of 169 rays were transformed into Zernike coefficients for different pupil sizes. The benefit from correcting spherical aberration at individual esopic pupils was investigated by canceling C4(0) in the sets of Zernike coefficients for 41 eyes implanted with spherical IOL.

RESULTS

Both the model eye and the real eye data predict that age-related miosis reduces spherical aberration in the eye implanted with a spherical IOL to approximately 1/3 of the spherical aberration at a 6-mm pupil. A reduction of similar magnitude occurs when spherical aberration-induced non-paraxial defocus is corrected by a spectacle lens. For natural mesopic pupils, canceling the Zernike C4(0) coefficient improved the objective image quality at a rate similar to changing defocus by 0.05 diopters. Average decentration and tilt levels diminish the lead of aspheric IOLs over spherical IOLs, depending on the direction of decentration.

CONCLUSIONS

The benefit from correcting spherical aberration in a pseudophakic eye is limited for some or all of the following reasons: wearing glasses, age-related miosis, tilt and decentration of IOL, small contribution of spherical aberration to all aberrations, and intersubject variability.