The influence of posterior capsule opacification on scanning laser polarimetry

Purpose To evaluate the influence of posterior capsule opacification (PCO) on GDx parameters in a population of pseudophakic, non-glaucomatous patients who underwent Nd:YAG laser capsulotomy (YLC). Methods The posterior capsules were photographed with a Topcon digital camera and each image was then entered into the EPCO 2000 software and evaluated independently by three examiners. The EPCO 2000 software was used to calculate the fibrosis index (FI) and the pearl index (PI) for the central 1.5, 2.5, and 3.5 mm of the posterior capsule. Scanning laser polarimetry was performed with GDx before and after YLC. We compared the GDx readings obtained before and after the YLC using paired Student's t-test. The parameters that varied significantly after YLC were subsequently used for regression analysis. Stepwise multiple linear regression was used to analyse the impact of the change in the amount of FI and PI on change in GDx parameters after YLC. Results In total, 158 patients were enrolled (74 men, 84 women). The mean age was 69.46 ±8.83 years (range 46-83 years). The interobserver agreement among the three experts was found to be good (repeatability coefficient R = 1.51, 1.49,1.49 for observer A vs B, A νs C, and B vs C respectively). One-sample Student's t-test show no difference between all GDx parameters before and after YLC except for Symmetry, Superior/Nasal ratio, Inferior Ratio, and Temporal-Superior-Nasal-Inferior-Temporal (TSNIT). Stepwise multiple regression showed that the two variables of greatest significance for changes in Symmetry were the FI in the central 1.5 and the PI in the central 3.5 mm (P = 0.02). Superior/nasal ratio was shown to be most strongly correlated to the FI in the central 1.5 mm and PI in the central 3.5 mm (P< 0.001), whereas the variable of greatest significance to Inferior Ratio was PI in the central 3.5 mm (P = 0.03). Finally, TSNIT was most strongly correlated to FI in the central 1.5 mm and FI in the central 2.5 mm (P< 0.001). Conclusion Presence of capsular fibrosis seems to be more clinically relevant in the central zone, whereas pearls tend to be clinically significant in the central 3.5 mm area. Hence, it might be worthwhile assessing the amount of PCO in pseudophakic patients when performing scanning laser polarimetry. Investigators should ensure that the type of PCO and the size of the area analysed are documented in the notes in order to interpret GDx findings appropriately.