EFFECT OF CORNEAL ASTIGMATISM ON CONTRAST SENSITIVITY OF MONOFOCAL 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 asse ss the influence of uncorrected corneal astigmatism on the contrast se nsitivity function (CSF) of mono- and multifocal IOLs, an ''optical im plantation'' of physical eyes with astigmatic corneas and IOLs was per formed in younger subjects. Methods The virtual image of physical eyes with a 40 dpt achromate as artificial cornea and the (M) IOL in a wat er bath was projected on the retina of the observer by means of an exa ctly adjusted video objective. Silicone lenses with defined astigmatis ms (+1; +2; +4; +6 dpt) were put in front of the achromate to produce an artificial corneal astigmatism. We compared results of a standard m onofocal 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 a ge: 27,4 y.) with the B-VAT II-SG Video Acuity Tester (Mentor O&O), wh ich uses sine wave gratings of five different spatial frequencies (1.5 ; 3; 6; 12; 20 cpd). Results Without astigmatic lenses, all IOLs showe d a mean CSF within the age-related norm, but the monofocal IOL yielde d significantly better results than both MIOLs at three spatial freque ncies (3; 6; 12 cpd). With additional astigmatic lenses of 2 dpt and m ore, mean CSF of all IOLs was below normal range, but there was no dif ference in the performance of the three lens styles. Conclusion CSF of MIOLs seems to be less sensitive to uncorrected corneal astigmatism t han CSF of the monofocal IOL. This suggests, that a higher preoperativ e astigmatism does not severly affect the image quality through a mult ifocal IOL.