Bifocal With Extended Depth of Focus Lens Combination Can Improve Stereopsis

A mix-and-match approach to intraocular lens (IOL) implantation can offer stable binocular visual outcomes with excellent static visual acuity, stereopsis, and dynamic visual acuity (both near and distance vision), according to a report published in International Ophthalmology.

Prior studies have shown combining multi-focal and extended depth of focus (EDOF) IOLs can provide good static vision, but this research demonstrates 5 lens combinations that can provide superior stereopsis and dynamic visual acuity using bifocal and EDOF IOLs.

Researchers enrolled in the prospective study included 292 eyes of 146 patients aged 50 to 65 years who received bilateral or blended cataract surgery approximately 1 week apart at an academic hospital in China. All patients displayed corneal astigmatism of 1.0 diopter (D) or smaller, axial length of 23 to 24 mm, and no coexisting ocular or systemic diseases that would affect outcomes. The researchers divided patients into 5 groups: bifocal in both eyes (MM, n=33 individuals), bilateral trifocals (TT, n=31), both eyes with EDOF (XX, n=34), bifocal with EDOF (n=25), and trifocal with EDOF (n=23).

Three months after surgery, spherical equivalent, contrast sensitivity, corrected distance visual acuity (CDVA), and static uncorrected distance visual acuity (UDVA) were comparable between all 5 groups. Uncorrected intermediate visual acuity (UIVA) differed (P =.006), with the MM group showing lesser UIVA than the other 4 groups. Regarding uncorrected near visual acuity (UNVA) differences (P =.038), the mix of bifocal and EDOF performed better than MM and trifocal-EDOF blend.

The bifocal-EDOF cohort also exhibited superior stereopsis at distance and near than the other groups. “This combination seems to be a good option for patients with high demands for binocular visual quality,” according to the researchers. The bifocal-EDOF combination was effective for dynamic visual acuity overall, although particular differences emerged.

For uncorrected distance dynamic vision at 24 frames per second (fps), the bifocal-EDOF and XX cohorts did better than the trifocal-EDOF group, although no differences arose at other speeds; 4 fps, 8 fps, or 12 fps. The bifocal-EDOF and XX combinations did best for uncorrected intermediate dynamic visual acuity, considering all frame speeds. Regarding uncorrected near dynamic vision, as speed increased from 8 to 24 fps, the bifocal-EDOF and XX groups did better than both MM and TT cohorts. Also, blended bifocal-EDOF outperformed trifocal-EDOF at 24 fps.

Previous studies differed from the current investigation’s finding of comparable static UNVA outcomes between bilateral EDOF with bilateral bifocals or trifocals. The investigators speculate this occurred due to this study’s target refraction of 0±0.25 D for bifocal and trifocal IOLs, and -0.5±0.25 D for EDOF —  with the best UNVA results of bilateral EDOF potentially coinciding with the “reserved diopter of myopia.”

Further, prior research suggests optimal static visual acuity and a continuous visual range may lead to good dynamic vision, allowing prediction of moving objects, and therefore reduction of lag in smooth-pursuit eye movements. 

Limitations of the analysis include different sample sizes of the five groups, lack of distinction between implantation in dominant and non-dominant eyes, and short follow-up. However, this is the first study that focuses on binocular stereopsis with mix-and-match IOLs.