Comparison of 2 Diffractive Trifocal 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. 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 to the patient. In clinical studies diffractive lenses resulted in a better outcome in terms of optical quality, better contrast sensitivity and lens photopic phenomena (dysphotopsia such as halos and glare) than in 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 that multifocal design. Since objects commonly viewed in this distance include computer displays and tablets, the intermediate distance has become a crucial part in daily life. As a consequence of poor intermediate visual acuity there is a need for spectacles for intermediate vision. 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 recently introduced, i.e. the trifocal lens. Trifocal lenses provide three focal distances, far, intermediate and near. This ideally results in even less spectacle dependence, including computer work. There are currently 3 trifocal designs available and are being used readily. One potential disadvantage of trifocal compared to bifocal IOLs is that near vision may be slightly poorer with the need for reading glasses with prolonged fine near work.

A slightly modified trifocal design has been recently introduced, that appears to have even better near vision than other trifocal designs as well as the potential for less dysphotopsia with a dilated pupil such as during the night.