Optical scattering measurements of laser induced damage in the intraocular lens

Abstract

This study optically determines whether the amount of light scatter due to laser-induced damage to the intraocular lens (IOL) is significant in relation to normal straylight values in the human eye. Two IOLs with laser-induced damage were extracted from two donor eyes. Each IOL had 15 pits and/or cracks. The surface area of each pit was measured using a microscope. For 6 pits per intraocular lens the point spread function (PSF) in terms of straylight was measured and the total straylight for all 15 pits was estimated. The damage in the IOLs was scored as mild/moderate. The total damaged surface areas, for a 3.5 mm pupil, in the two IOLs were 0.13% (0.0127 mm(2)) and 0.66% (0.064 mm(2)), respectively. The angular dependence of the straylight caused by the damage was similar to that of the normal PSF. The total average contribution to straylight was log(s) = -0.82 and -0.42, much less than the straylight value of the normal eye.The straylight due to normal levels of laser induced damage of the IOL is much lower than normal straylight values found clinically for the normal eye and may therefore be considered not significant.

Figure 1. Schematic representation of a) the macroscope setup with a dark field ring illuminator; and b) the setup to quantitatively measure scattered light under different angles.

Figure 2. Dark field images of the IOLs acquired with the macroscope setup.

Dark regions represent low scattering and light areas represent high scattering. In both images the laser pits and cracks are demarcated. a) IOL with 15 damaged areas with a circumference of approximately 3.5 mm; and b) IOL also with 15 damaged areas, but a circumference of 2–2.5 mm.

Figure 3. Microscope magnifications of several laser induced damaged areas in the IOLs from figure 2 .

a) area 3 in figure 2a; b) area 5 in figure 2a; c) area 1 in figure 2b; d) area 4 in figure 2b. Laser-induced damage was scored as mild damage except for c) which was scored as moderate damage.

Figure 4. PSF of 6 individual pits (bottom 6 curves in each figure) for the IOL of a) figure 2a and b ) figure 2b .

The line with closed circle symbols represents the estimated total contribution of all pits in the IOL. The top PSF illustrates the PSF-model, according to the CIE, of a 35–year-old individual.