Eyeworld

JULY 2019 | EYEWORLD | 17 EYEWORLD JOURNAL CLUB Benyam Kinde, MD, and Megan Law, MD Source: UCSF lenses were initially used as controls, prior to heat exposure. A subset of the total lenses used in this study underwent multiple treatments in order to increase the range in the number of glistenings. IOLs were then photographed and the number and size of induced glistenings were calculated. Subsequently, lenses were graded: grade 0 (no glistenings), grade 1 (1–100 MV/ mm 2 ), grade 2 (101–200 MV/mm 2 ), grade 3 (201–500 MV/mm 2 ), and grade 4 (more than 500 MV/mm 2 ). The MTF and the Strehl ratio were evaluated at aperture diameters of 3 mm and 4.5 mm. The MTF, which is a measure of contrast transfer from the object to image, was determined using three discrete spatial frequen- cies (20, 50, and 100 lp/mm). The Strehl ratio is another measure of optical performance and is calculated as the peak focal intensity in aber- ration versus an ideal system . Both MTF and Strehl ratio range from 0 to 1 with higher values representing better optical systems. Glistenings were observed in all 38 IOLs. The mean glistening number +/– standard deviation (MV/mm 2 ) was 74±12.7 (grade 1), 142±22.2 (grade 2), 297±76.2 (grade 3), and 1509±311.9 (grade 4). The mean glistening diameter ±SD was 15.31±3.13 µm (range: 7.33–24.74 µm), comparable to previous studies. 2, 9 There were no significant differenc- es between the MTF values of the clear IOLs and those with grade 1–3 glistenings (Wilcoxon test, p>0.05). Grade 4 IOLs had lower MTF levels compared to clear IOLs (Mann-Whitney U test, p<0.01). The differences were 0.011 (25 lp/mm), 0.024 (50 lp/mm), and 0.048 (100 lp/ mm) for the 3-mm aperture, and 0.056 (25 lp/ mm), 0.071 (50 lp/mm), and 0.059 (100 lp/mm) for the 4.5 mm aperture. In IOLs with grade 4 glistenings, the Strehl was lower compared to controls by 0.068 (3 mm) and 0.096 (4.5 mm; Mann-Whitney U test, p<0.01). The decreased Strehl ratio for grades 1–3 was not statistically significant (Wilcoxon test, p>0.05). G listenings are fluid-filled microvac- uoles that develop within IOLs postoperatively. They are appreci- ated on slit lamp as shiny speckles, and various grading techniques have been employed to better objective- ly categorize severity. Glistenings are generally thought to develop secondary to water vapor detachment and accumulation within polymer voids of IOLs. As light passes through the IOL, it is refracted and scattered at the water-polymer interface. 1 The impact of glistenings on visual performance has been a matter of controversy. While Waite et al. and Hayahi et al. did not demonstrate a significant difference in visual acuity, other groups have reported effects on visual acuity and/or high contrast sensitivity. 2, 3, 4, 5, 6, 7. In this in vitro study by Weindler et al., the authors attempt to objectively assess the effect of various clinical grades of glistenings on image quality by calculation of the modulation transfer function (MTF) and Strehl ratio, two metrics of IOL image quality. Weindler et al. obtained 38 monofocal hydrophobic acrylic AcrySof SA60AT 21.0 D IOLs (Alcon) for this study. Glistening formation was induced by exposing lenses to a temperature change over time. Of the 38 IOLs used in this study, 20 Review of "The impact of glistenings on the optical quality of a hydrophobic acrylic intraocular lens" continued on page 18 by Megan Law, MD, and Benyam Kinde, MD Saras Ramanathan, MD Residency program director University of California, San Francisco (UCSF) The question of whether and by how much moderate to severe glistenings affect visual quality is difficult to determine. I asked the UCSF residents to review this study and literature review that appears in the July issue of JCRS. —David F. Chang, MD, EyeWorld Journal Club editor Contact information Ramanathan: Saras.Ramanathan@ucsf.edu

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