Optical imaging quality change of multifocal intraocular lens following Nd: YAG laser damage

Abstract

Objective To study the optical imaging quality of multifocal intraocular lens (IOL) following Nd: YAG laser damage. Methods Three hydrophobic acrylate discs used to make multifocal IOL were placed in line, and the Nd: YAG laser was used to emit the posterior surface, mid-plane and anterior surface of the discs by gradually increasing the emitting energy to determine the damaged threshold energy of various planes.Eight multifocal IOLs were divided into 2 groups.IOL damage models were established by emitting 12 points along 12 clocks on circle of 3.0 mm in diameter in the group 1 (IOLs NO.1, 2, 3, 4) and 6 points with 1-clock interval on circle of 1.0 mm in diameter in the group 2 (IOLs NO.5, 6, 7, 8) with Nd: YAG laser.The modulation transfer function (MTF), line spread function (LSF) and United States air force (USAF) test target images of the IOLs were tested under the optical aperture at 2.0, 3.0 and 4.5 mm. Results The damage thresholds of laser power were not significantly different among three hydrophobic acrylate discs (Fgroup=1.100, P=0.337), and the thresholds were significantly different among different planes in the discs (Fposition=195.279, P=0.000), with the highest damage threshold in the anterior surface and the lowest damage threshold in the mid-plane of the discs(all at P<0.01). The shifts of far focus and near focus MTF curves, LSF curves and USAF target images of the IOLs under the 2.0, 3.0 and 4.5 mm optical aperture after laser damage were in coincidence with those before laser damage both in group 1 and group 2.The glare phenomenon of the USAF target image was observed at near focus under the 4.5 mm optical aperture both before and after laser damage. Conclusions Multifocal IOL is vulnerable to injury when the laser beam focuses on the mid-plane, and the anterior surface of IOL can tolerate certain degree of damage.In standard model eye, the MTF curves, LSF curves and USAF target images of multifocal IOL was not impacted by laser induced spots injuries under different pupil diameters. Key words: Nd: YAG laser; Intraocular lens; Imaging quality; Modulation transfer function; Line spread function; United States air force test target; Standard model eye