Trifocal IOLs useful for intermediate vision

Two trifocal IOLs (AT LISA tri, Carl Zeiss Meditec; FineVision, PhysIOL) enabled patients in whom they were used to have "a useful third focus for intermediate vision," but they also resulted in increased background halos and reduced distance visual quality for users compared with the vision experienced by recipients of two powers (+2.5 D and +3.0 D) of a multifocal IOL (ReSTOR, Alcon), according to new research published in Clinical Ophthalmology. Three of the four authors work for Alcon Research.

The researchers used a Badal optometer and a Snellen visual acuity chart to evaluate all of the implants for resolution, image quality and photic phenomena. They found that resolution equivalent to 20/40 Snellen visual acuity was achieved over almost all of the viewing distance range in those receiving the trifocal implants, but background shadows were more noticeable for those with the trifocal lenses than they were for study participants receiving the multifocal lens.

The authors obtained simulated headlight images using a modulation transfer function (MTF) bench and a 50-μm pinhole target. They determined far, intermediate, and near distance MTF values using vertical and horizontal slits.

The researchers found that distance MTF peaks at 20/20 Snellen–equivalent spatial frequency were greatest for the multifocal IOLs. The near MTF peak with the +2.5 D multifocal IOL occurred at 53 cm and had a 20/20 Snellen–equivalent value; this was lower than the near peaks of the other study lenses but higher than the intermediate foci of both of the trifocal IOLs.

"Based on this laboratory simulation," the authors write, "the ReSTOR +3.0 D is expected to provide high-quality distance and near vision, with a low propensity for halos. The ReSTOR +2.5 D is expected to provide the best distance vision, with low halo intensity and intermediate vision around 50 to 60 cm. The two trifocal IOLs provide improved intermediate vision in the 70 to 80 cm range, although this benefit may come at the expense of increased nighttime halos."

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