Abstract
Purpose:
Calcification and snowflake degeneration are causes of postoperative opacification of hydrophilic acrylic/silicone and polymethylmethacrylate (PMMA) intraocular lenses (IOLs), respectively, causing significant forward light scattering and generally require IOL explantation. Light scattering of hydrophobic acrylic lenses is due to subsurface nanoglistenings (SSNG), generally not leading to explantation. We test the hypothesis that the effect of calcification and snowflake degeneration on stray light and other optical quality indicators is a different phenomenon and more significant than that of SSNG.
Methods:
14 IOLs were explanted from living eyes due to calcification (13 hydrophilic acrylic, 1 silicone), 4 PMMA IOLs were explanted because of snowflake degeneration. 17 single-piece AcrySof (Alcon) IOLs were removed from cadaver eyes exhibiting SSNG (11 with a blue light filter - BLF - and 6 without). The forward scattering of IOLs, including new IOL controls was measured using a Complete Angle Scatter Instrument; stray light values at various angles were calculated. The Modulation Transfer Function (MTF) was obtained with an optical bench; a Badal optometer was used to capture letter chart images through the lenses.
Results:
Average stray light values (Log (s)) at a scattered angle of 10 degrees were measured as 1.629 +/- 0.465 for PMMA IOLs (control PMMA = 0.258), 1.791 +/- 0.370 for hydrophilic acrylic IOLs (control hydrophilic acrylic = 1.335), and 1.539 for the silicone lens (control 0.418). The values for the AcrySof IOLs were 1.036 +/- 0.270 for BLF lenses, and 0.975 +/- 0.264 for non BLF lenses (controls 0.223 +/- 0.229). MTF and Badal image contrast were drastically reduced in lenses with calcification and snowflake degeneration, but were similar to controls (no SSNG) in AcrySof lenses.
Conclusions:
Studies from van den Berg et. al. find the impact of stray light in human vision, with serious hindrance above 1.47 (Log (s)). Stray light in hydrophobic IOLs due to SSNG is well below the value of stray light hindrance of 1.47 (no lens with a value ≥ 1.47), which would not cause noticeable visual impairments. Based on our results stray light due to calcification and snowflake degeneration reduced MTF and image contrast and stray light due to SSNG did not.