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Accuracy of corneal power measurement with rotating Scheimpflug camera combined with placido disc corneal topography after myopic laser refractive surgery

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Session Details

Session Title: Anterior Segment Imaging II

Session Date/Time: Tuesday 25/09/2018 | 08:00-10:30

Paper Time: 09:56

Venue: Room A4

First Author: : E.Yassa TURKEY

Co Author(s): :    C. Unlu                    

Abstract Details


Accurate measurement of corneal power (CP) in eyes which had undergone myopic excimer laser surgery previously is crucial for prevention of refractive error after cataract surgery. Recently, ray tracing (RT) has been suggested as a mean of directly measuring CP. Purpose of this study is to investigate the accuracy of RT provided by Sirius anterior segment evaluation system (CSO, Florence, Italy).


Asya Eye Medical Centre


We reviewed the medical records of 59 eyes of 31 patients who had undergone refractive laser surgery for myopia retrospectively. We collected different CP values calculated by RT, which was called mean pupil power (MPP) by manufacturer, and simulated keratometry (sim K) value using Sirius according to entrance pupil diameter (ranging from 2,5 to 7 mm). We compared these values with that of clinical history method (CHM).


Using one-way analysis of variance with Dunnett’s multiple comparisons test; mean 4,5 mm MPP (40.11±1.96 diopters [D]), 5 mm MPP (40.31±1.92 D) and 5,5 mm MPP (40.54±1.90 D) values were not significantly different from that obtained with CHM (40.31±1.99 D) [p>0.05]. Using Pearson correlation, 4,5 mm MPP, 5 mm MPP and 5,5 mm MPP values were significantly correlated with CHM (r: 0.907, 0.906, 0.905; respectively, p<0.05). Sim K significantly overestimated CP (0.53±0.84 D, p<0.001). Linear regression showed that preoperative spherical equivalent significantly influenced the accuracy of Sirius (p<0.05).


Direct measuring CP within the diameter of entrance pupil 4,5 mm, 5 mm and 5,5 mm by using ray tracing in eyes which had undergone myopic excimer laser surgery has given similar and consistent results with that of CHM, which is classically considered to be gold standard. Based on our results, 5 mm MPP seems to be the best value provided by Sirius. However, the amount preoperative spherical equivalent might influence the accuracy of the device yet using MPP instead of CHM might be source of error in eyes which had undergone myopic refractive laser surgery in assessment of CP.

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