[Multifocal intraocular lenses--an assessment of current status]

Besides the diffractive multifocals, which produce a second focus for near vision by means of diffraction rings, there are different refractive multifocal IOL types with 2-7 refractive zones or an aspheric/spherical construction principle. Long-term results: 2 years after implantation of diffractive multifocal IOLs, the corrected distance and near acuities were unchanged compared to the 3-month results. The uncorrected distance acuity was, however, slightly decreased due to a minus shift of refraction to -1.2 D. The contrast sensitivity was improved after 2 years. Multi- versus monofocal IOLs: After diffractive multifocal IOL implantation, the near acuity with distance correction only was markedly improved compared to monofocal IOLs. All other acuity data did not differ between multi- or monofocal lenses. The contrast sensitivity (at low contrasts and high spatial frequencies) and mesopic visual acuity (without and with glare) were reduced compared to monofocal pseudophakic eyes. Near aniseikonia and binocular functions: In unilateral multifocal pseudophakia (monofocal IOL in fellow eye), a near aniseikonia up to 8% was found. The width of fusion was significantly lower than in bilateral multifocal pseudophakia, whereas the stereopsis showed no difference. Determinants of bifocal function: In 7.1% of our cases, no bifocal function (BFF) was present after implantation of diffractive multifocal IOLs. These patients exhibited a significantly higher age as well as higher pre- and postoperative astigmatism, when compared to patients with good BFF. Optical performance of different multifocal IOLs: By means of an optical system, described by Reiner, images of intraocular lenses can be projected into the eye ("optical implantation"); thus, the optical performance of IOLs can be judged subjectively. Using this method, the refractive 2- and 3-zone models performed best within the multifocal group (contrast sensitivity not significantly worse than that of monofocal IOL), when viewing a low-contrast chart (Regan 4%). All other multifocal lenses (diffractive, aspheric/spherical, refractive 5- and 7-zone models) were significantly inferior to the monofocal IOL.

Implantation of multifocal IOLs should presently be restricted to special indications, particularly to the distinct patient request to dispense with wearing near or bifocal glasses, if possible. Because of the reduction in contrast sensitivity and mesopic vision and the increased glare sensibility, multifocal IOLs should not be implanted especially in professional car drivers. There are, however, differences in optical performance between the various multifocal IOL types. Further improvements, in particular concerning lens technology, will presumably extend the present spectrum of indications.