Purpose: Extended depth-of-focus (EDoF) and multifocal intraocular lenses (IOLs) are usually implanted for patients who request spectacle independence after surgery. Despite general success, a major cause of patient dissatisfaction is the appearance of photic phenomena mainly produced by diffractive profiles. The aim of this work is to study in vitro the halo formation in a variety of IOLs.
Methods: The experimental system consisted of a 530 nm LED light illuminating a 200 μm pinhole at the focal point of a collimating lens. A tunable lens was then used to make through-focus measurements. The IOL was placed into a realistic physical model eye with a cornea having +0.28 μm of spherical aberration (at 6 mm aperture) and a 4.5 mm pupil. A camera was placed at the retinal plane of the eye. Images with different exposure times were obtained and fused to get high dynamic range (HDR) images, both at best focus and through-focus (range ±4 D). Performance was assessed via brightness and halo size calculations. The tested IOLs included: monofocal, enhanced monofocal, diffractive and refractive EDoFs (including inverted meniscus IOLs), and diffractive trifocals. Lens power was between 19 D and 22 D.
Results: All diffractive IOLs caused halos with a characteristic ring structure, while refractive lenses showed less defined halo structures. Figure 1 shows examples for three types of lenses. The monofocal and enhanced lenses produced halos with a radius between 0.35 to 0.46 degrees. The halo radii of the non-diffractive EDoF lenses ranged between 0.44 and 0.7 degrees, whereas diffractive lenses had halo radii ranging from 0.83 to 1.1 degrees. The brightness of the straylight was 67-70% dimmer than the central image for the refractive lenses, while for the diffractive it was 56-58% dimmer. The through-focus images show that the halo size was larger for the diffractive lenses than for the rest of the IOLs tested at any defocus. Halo size remained approximately constant regardless of the induced defocus.
Conclusions: Of the measured lenses, the diffractive IOLs exhibited a characteristic halo. The inverted meniscus lenses’ performance, along with the other non-diffractive lenses, was comparable to that of a monofocal lens. This on-bench test can serve as an indication of the potential impact on patient satisfaction.
