Erroneous optical performance of diffractive intraocular lenses obtained with near-infrared light

Abstract

Purpose : Multifocal intraocular lenses are increasingly frequently implanted during cataract surgery or presbyopic lens exchange. There are several optical vision testing devices on the market, of which some even assess the retinal image quality. However, some devices use near-infrared light to measure the patient’s visual performance. This is valid for refractive monofocal and possibly for refractive multifocal intraocular lenses, too, but is erroneous for diffractive lenses. To prove this assertion, the through-focus intensities and energy efficiencies of an exemplarily selected diffractive trifocal intraocular lens were measured using green and infrared light and subsequently compared.

Methods : Using an in-house developed optical bench, the three-dimensional point spread function of a water-immersed trifocal intraocular lens in a model eye is measured for green (530 nm) as well as for near-infrared light (780 nm) and different pupil sizes ranging from 2.44 mm to 5.87 mm. A dedicated algorithm for rotationally symmetric intraocular lenses calculates the through-focus intensities and energy efficiencies of the foci in dependence on pupil size.

Results : The through-focus intensities obtained with green light show a trifocal behavior for all pupil sizes except for the smallest pupil, where the far and intermediate foci overlap. Using near-infrared light, the through-focus intensities for 3.42 mm and above show an intense far focus and only very weak near and intermediate foci in the order of a fifth of the far focus intensity. For smaller pupil sizes, the foci are stretched over a wide range, overlap having low intensities. The energy efficiencies decrease with pupil size. For green light, the far focus slightly dominates, and the near and intermediate focus efficiencies are almost equal. Using near-infrared light, the far focus efficiency is about four to five times higher than the other foci.

Conclusions : The results provide experimental evidence of the wavelength dependent imaging properties of diffractive intraocular lenses. Representatively, we demonstrate a trifocal lens design turning into a monofocal lens at 780 nm. Hence, optical vision testing devices operating at a wavelength in this range give wrong results leading to erroneous assumptions concerning the patient’s postoperative visual performance. Interpreting these findings in terms of clinical recommendations is a severe pitfall.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.