Optical performance of multifocal intraocular lenses

Reduced contrast sensitivity, glare disability and insufficient bifocality are the main drawbacks of multifocal intraocular lenses (IOL). The bilateral implantation of diffractive IOL with an asymmetrical light distribution for distance and near focus is an alternative concept that aims to improve the contrast sensitivity and bifocality of conventional multifocal IOL. The optical performance of monofocal (PhacoFlexII SI40) and multifocal IOL (Array SA40N; Acri.Twin 737D/733D) was quantitatively assessed in 18 healthy probands and qualitatively determined by digital photographic recording using an optical apparatus, the "physical eye", according to Reiner and Jacobi. Vision examination included standard tests of distance and near visual acuity, contrast sensitivity and low contrast visual acuity testing under varying pupil size using a video acuity tester. Distance visual acuity was significantly superior with the SI40 and distant-dominant 737D compared to the SA40N and near-dominant 733D. At near, the 733D had the best performance. Contrast sensitivity was better with the 737D than the SA40N when both were compared with the SI40. No normal contrast sensitivity could be determined with the 733D because of the optical phenomenon of 'spurious resolution'. Variation in pupil size had less impact on contrast acuity with the Acri.Twin IOL compared to the SI40 and SA40N. Photographic testing revealed better edge contrast with the Acri.Twin than the SA40N. The optical performance of multifocal IOL correlates with the properties of physical light distribution. Differences in edge contrast may be discerned using photographic recording.