Effects of Intraocular Lens Opacification on Light Scatter, Stray Light, and Overall Optical Quality/Performance

To evaluate light scatter and stray light in intraocular lenses (IOLs) explanted because of postoperative opacification (13 calcified hydrophilic acrylic, 1 calcified silicone, and 4 polymethylmethacrylate [PMMA] lenses with snowflake degeneration), as well as effect of opacification on other optical quality/performance indicators, in comparison with controls.

The Complete Angle Scatter Instrument (CASI) scatterometer was used to measure the forward light scattering (FLS) of the IOLs, and the stray light values at various angles were calculated from the measured FLS. Modulation transfer function (MTF) was obtained with an optical bench, and a Badal optometer was used to obtain letter chart images through the lenses. Back light scatter and light transmittance were also measured.

Average stray light values (Log (s)) at a scattered angle of 10° were 1.79 ± 0.37 for hydrophilic acrylic IOLs (controls 0.36 ± 0.05), 1.53 for the silicone lens (control 0.41), and 1.62 ± 0.46 for PMMA IOLs (control 0.25). Stray light was significantly higher for explanted opacified lenses (N = 18) in comparison with controls (N = 7; two-tail P < 0.001 at 10°). Modulation transfer function and Badal image contrast were drastically reduced in lenses with calcification and snowflake degeneration.

Different studies described the impact of stray light in human vision, with serious hindrance above 1.47 Log (s). Lenses explanted from patients because of clinically significant opacification are associated with a considerable increase in light scatter and stray light, as well as with a decline of other optical quality/performance indicators.