Optical testing of intraocular lenses using a combined laser-ray tracing and optical coherence tomography system

Abstract

Purpose : To evaluate the feasibility of assessing the power and aberrations of monofocal and multifocal intraocular lenses (IOLs) using a laser-ray tracing approach.

Methods : Data were acquired on a 28.5 D aspheric monofocal IOL (Acrysof IQSN60WF, Alcon) and a 21.5 D aspheric diffractive multifocal IOL with 4.0 D add (Acrysof IQ ReSTOR SN6AD3, Alcon). The IOLs were immersed in balanced salt solution and supported by a custom lens holder, with their anterior surfaces facing the incident beam of a combined Laser-Ray Tracing and Optical Coherence Tomography (LRT-OCT) system (wavelength: 880 nm). The system acquires OCT images and measures the slopes of rays refracted through the lens for on-axis and off-axis incidence (Ruggeri et al, Biomed Opt Exp 2018,9(8) 3834-3851). The exit ray slopes (Figure 1) were calculated from recordings of spot patterns as a function of axial position using an image sensor mounted on a positioning stage below the IOL chamber. Each lens was tested three times with a raster scan covering a 6 mm zone with a spacing of 0.5 mm. The ray slopes were used to calculate the wavefront aberration maps of the IOLs. Lens power was calculated using two different methods: 1) by finding the axial position that minimizes the root-mean-square diameter of the spot pattern formed by the 49 central rays of the raster scan corresponding to a central 3 mm zone; and 2) by using the defocus term of the reconstructed wavefront.

Results : The measured power was 27.0±0.2 D (method 1) and 25.7±0.4 D (method 2) for the monofocal IOL and 20.5±0.4 D (method 1) and 19.6+0.04 D (method 2) for the multifocal IOL. The difference between nominal and measured power is due in part to dispersion effects and to differences in methods to quantify lens power. Spherical aberration for a 6 mm diameter pupil was -0.35±0.07 μm for the monofocal IOL and -0.21±0.02 µm for the multifocal IOL. The diffractive structure of the multifocal appears as a hyper-reflective zone in the OCT image (Figure 2). The add provided by the diffractive zone of the multifocal IOL could not be detected with the selected scan parameters.

Conclusions : The results demonstrate that the optical characteristics of aspheric monofocal IOLs can be assessed using laser-ray tracing. The LRT scan pattern must be optimized to capture multifocality.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.