Letters: Multifocal concerns

We refer to the article entitled ‘Save the Presbyope: extended depth of focus contact lenses’ published in the contact lens edition of Optician on August 6, 2021 and the interview with Visioneering Technologies’ CEO, Dr Stephen Snowdy, entitled ‘Convincing arguments’ published on September 3, 2021.

We have concerns regarding both, in that the optics and mode of action of leading modern centre near multifocal soft contact lenses (MF SCLs) have not been described correctly. In figure 5 of the first publication these lens designs are described as having three zones, which would render them essentially trifocals. In the interview Dr Snowdy describes them as being a concentric ring design that ‘may contribute to diffraction and diminished performance.’ In reality, most leading MF SCLs have a progressive aspheric design1,2 with a continuous power variation across the optical profile, giving a smooth spread of focus from distance through intermediate to near, with no diffraction occurring, but adding spherical aberration into the optical system.2