Peripheral defocus profile of spherical and aspheric intraocular lenses

Abstract

Purpose : Studies have shown a degradation of peripheral retinal image quality in pseudophakic eyes, which can affect visual function. The goal of this study is to measure the peripheral defocus profile of monofocal intraocular lenses (IOLs) and compare it with theoretical predictions.

Methods : Peripheral defocus profiles of monofocal spherical (PMMA, Appasamy Associates) and aspheric (Acrysof, Alcon Laboratories) IOLs were measured. The power of these IOLs ranged from 17D to 25D. The IOLs were placed on a custom-built holder immersed in balanced salt solution in the test chamber of a laser ray tracing (LRT) aberrometer that enables measurements at oblique angles at a wavelength of 880 nm (Ruggeri et al, Biomed Opt Exp 2018). LRT data were acquired at incidence angles ranging from -30° to +30° in 5° increments using a 3 mm x 3 mm raster scan with 0.25 mm spacing (169 rays). The position of the best focus (minimum RMS spot size of the 169 incident rays) was calculated from the LRT spot patterns recorded at 9 different axial positions beneath the test chamber. The power and relative peripheral defocus at each angle were calculated from the measurements. Results were compared with predictions of the Coddington equations for a thin lens with aperture stop located at the lens.

Results : For both spherical and aspheric IOLs, power increases significantly as the incidence angle increases (Figure 1). Peripheral defocus increases as the IOL power increases (Figure 2). The difference in defocus between spherical and aspheric IOLs was 0.9±0.2D on average. Relative peripheral defocus at ±30° increases from 4.9D for a 17.5D IOL to 7.4 D for a 24.5D IOL for the spherical IOLs and from 4.9D for a 17D IOL to 7.4 D for a 25D IOL for the aspheric IOLs. The measured peripheral defocus closely matches the tangential image from the Coddington equations. The mean difference between measured and predicted tangential power at ±30° is +0.50±0.16 D for spherical IOLs and -0.40D±0.10D for aspheric IOLs, independent of IOL power.

Conclusions : Both spherical and aspheric IOLs have significant peripheral defocus, which increases with IOL power.

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

 

Figure 1: Peripheral defocus profile of spherical (PMMA, Appasamy) and aspheric (Acrysof, Alcon) IOLs.

 

Figure 2: Effect of IOL power on peripheral defocus of aspheric acrylic (black dots) and spherical PMMA (red squares) IOLs. Solid lines are the tangential image defocus from the Coddington equations.