[Contrast sensitivity and defocus curve with various bifocal-IOL]

Simultaneous vision, the basic principle of all bifocal intraocular lenses (IOLs), provides increased depth of focus but also causes a loss in contrast. We therefore measured contrast acuity (CA) (Regan Charts) and the defocus curve at different pupil sizes in 14 patients with a TRUE VISTA bifocal IOL (TV) (Storz Co.), 10 patients with a 3M diffractive bifocal IOL (3M) (3M Co.) and 9 patients with a Nordan Aspheric Varifocal Silicone IOL (VF) (Wright Medical Inc.). CA at distance focus was best with VF; next was TV, and 3M showed the lowest values. At near focus, CA was best with 3M; next was TV, and VF showed the lowest values. Differences between VF and 3M were significant (P = 0.05; t-test). CA at near focus was significantly lower than at distance focus with TV and VF (TV: P = 0.0001; VF: P = 0.005). Pseudoaccommodation was 4.5 D with TV and 3M and 3D with VF. In conclusion, distance CA was best with VF but pseudoaccommodation was not sufficient for reading. Near CA was best with 3M while distance CA was somewhat reduced. TV showed good distance CA while near CA was still sufficient. TV therefore seems to provide a good compromise.