Glare Effects From Diffractive Steps Of An Extended-Depth-Of-Focus Intraocular Lens

Diffractive optics has often been associated with glare complaints ascribed to the simultaneous projection of two or more foci. However, the contribution of a diffractive profile to light scattering has also been expected to be important. This study aimed to quantify straylight effects from an echelle element featuring 9 diffractive zones.

The David J. Apple Center for Vision Research, Department of Ophthalmology, University of Heidelberg, Heidelberg, Germany.

Light scattering from a Tecnis Symfony intraocular lens (IOL) was measured using a goniometer-based setup up to 7.5°. Two samples were assessed, and the average value ± standard deviation was reported. Recorded images of a circular aperture were processed to determine the contribution of each diffractive step to straylight. The zone border was set to fall halfway between each detected diffractive step. Besides the central (monofocal) and 9 annular zones, a full aperture with a diameter identical to the outer diameter of the last (9th) zone was also assessed. The proportion of scattered light was calculated to derive the loss of light.

Material scattering was close to zero; however, each echelle zone acted as a scattering source. A nearly gradual straylight increase was found, with the zone number showing peak intensity between 3° and 3.75°. At this range, a straylight parameter of 1.27 ±0.06 logs was found at the full aperture. Light scattering at diffractive steps yielded an estimated 6.2% ±0.1% light loss.

The refractive-lens base exhibited only minimal scattering effects. However, the diffractive pattern introduced straylight elevation, which may result in glare phenomena. The location of the peak intensity can make the clinical measurement of these effects challenging. Since the scattered light is missed in the retinal image, its proportion reflects the light loss.