Comparison of Visual Outcomes After Bilateral Implantation of a New Extended Depth of Focus (EDOF) IOL Twinset With Bilateral Standard EDOF IOLs

Spectacle independence is a central aim in modern cataract surgery. Although bilateral monofocal IOL implantation, aiming for emmetropia or low myopia, leads to high levels of patient satisfaction in distance vision, spectacle dependence for reading and other near vision tasks is the usual result.

The option commonly used to achieve spectacle independence are multifocal intraocular lenses (IOLs). Multifocal IOLs either use a refractive or diffractive design or a combination of both or segmented asymmetric optics. The principal of the refractive design is based on changing the route of light rays by thickness, curvature and optical density of the lens. The principal of diffractive design is based on scattering of light rays when passing an edge in the material of the lens. Usually, the characteristic diffractive ring patterns are incorporated on the posterior surface of an IOL, whereas the anterior lens surface remains purely refractive. One potentially negative aspect of multifocal refractive IOLs is pupil size dependence, another is loss of light energy to higher order diffraction which is not useful for the patient. In clinical studies, diffractive lenses resulted in a better outcome in terms of optical quality, better contrast sensitivity, and less photic phenomena (dysphotopsia such as halos and glare) compared to refractive lenses.

Until recently multifocal lenses were typically bifocal with a focus assigned to near and a focus assigned to far vision. However, the intermediate working distance is poorly covered by the bifocal design. Since objects commonly viewed in this distance include computer displays and tablets, the intermediate distance has become a crucial part in daily life. Variations in the addition of power chosen for near vision provided some intermediate visual acuity, but still suboptimal. Therefore, a new concept of multifocality has been introduced, the trifocal lens. Trifocal IOLs provide three focal distances: far, intermediate, and near. This ideally results in even less spectacle dependence, including for computer work. However, one potential disadvantage of trifocal IOLs is slightly poorer near vision compared to bifocal IOLs with need for reading glasses for prolonged fine near work and loss of contrast sensitivity in the intermediate distance.

A better intermediate performance concerning contrast vision compared to trifocal IOLs can be reached using enhanced depth of focus (EDOF) lenses. These IOLs have an extended far focus area which reaches to the intermediate distance, providing high-quality vision over a continuous range of focus, rather than distinct foci with blur in between.

To provide similar outcomes to trifocal IOLs, mix-and-match of additions ("blended vision") is another option, in which additions of multifocal IOLs between both eyes differ. The idea behind it is to improve the contrast in the intermediate distance compared to trifocal IOLs. The combination of +1.75D/ +4D10 and +1.5D/ +3D11 successfully achieved a regular defocus curve, but patient's subjective binocular comfort was not determined. To preserve the binocular balance between the eyes, a difference in addition of 0.5D was proposed and the combination of +2.5D/ +3D showed similar results as trifocal IOLs, except in the intermediate range of -1D and -1.5D.