Vision with bifocal intraocular lenses.

The laboratory and clinical results of tests of different bifocal intraocular lenses (BIOLs) are compared. Included are two-zone refractive BIOLs with a central near zone and an annular distance zone (group 1); three-zone refractive BIOLs with a central distance zone, an annular near zone, and a peripheral distance zone (group 2); diffractive BIOLs (group 3); multizone refractive BIOLs (group 4); and other BIOLs (group 5). All BIOLs cause a significant loss of image contrast and acuity at low contrast. The incidence of visual side effects (e.g., halos, glare) varies but is significantly higher than that obtained with monofocal IOLs. On the other hand, BIOLs provide a depth of focus of 3-4 D as compared with only 1.5 D for monofocal IOLs. In group 1, distance vision is reduced in bright light, which limits the clinical use of these BIOLs. In group 2, distance vision is better than near vision. Thus, a temporary near add is required in some cases. In group 3, distance and near vision are similar, but the incidence of visual side effects is higher than that in group 2. Only BIOLs of groups 2 and 3 can be recommended for clinical use in selected patients. Not enough data are currently available on the other groups. Patient selection is the most critical factor for BIOLs. Ideal patients are relatively young and active, are highly motivated, show no ocular pathology, and have a normal pupil, an axial length of 22-24.5 mm, and a corneal astigmatism of less than 1 D. Reduced image contrast, mainly at near focus, and visual side effects must be acceptable. Bilateral implantation yields the best results. A monofocal fellow eye is a definite contraindication. In summary, BIOLs cannot replace monofocal IOLs. However, they provide a valuable alternative in selected patients.