Effect of corneal astigmatism on contrast sensitivity of mono- and multifocal pseudophakic eyes - A theoretical study with an optical system: Physical eyes

Background Several clinical studies indicate, that the visual function of multifocal IOLs (MIOL) is impaired by corneal astigmatism. To assess the influence of uncorrected corneal astigmatism on the contrast sensitivity function (CSF) of mono- and multifocal IOLs, an ''optical implantation'' of physical eyes with astigmatic corneas and IOLs was performed in younger subjects. Methods The virtual image of physical eyes with a 40 dpt achromate as artificial cornea and the (M) IOL in a water bath was projected on the retina of the observer by means of an exactly adjusted video objective. Silicone lenses with defined astigmatisms (+1; +2; +4; +6 dpt) were put in front of the achromate to produce an artificial corneal astigmatism. We compared results of a standard monofocal IOL (Pharmacia 811B), a multizone progressive MIOL (AMO Array SSM-26NB) and a diffractive MIOL (Pharmacia 811E). CSF through these IOLs in the physical eyes was measured in ten healthy subjects (mean age: 27,4 y.) with the B-VAT II-SG Video Acuity Tester (Mentor O&O), which uses sine wave gratings of five different spatial frequencies (1.5; 3; 6; 12; 20 cpd). Results Without astigmatic lenses, all IOLs showed a mean CSF within the age-related norm, but the monofocal IOL yielded significantly better results than both MIOLs at three spatial frequencies (3; 6; 12 cpd). With additional astigmatic lenses of 2 dpt and more, mean CSF of all IOLs was below normal range, but there was no difference in the performance of the three lens styles. Conclusion CSF of MIOLs seems to be less sensitive to uncorrected corneal astigmatism than CSF of the monofocal IOL. This suggests, that a higher preoperative astigmatism does not severly affect the image quality through a multifocal IOL.