Objective To assess the repeatability and accuracy of two instruments for measuring corneal refractive power in myopic eyes： the Scheimpflug-Placido topographer （Sirius） and the Keratron topographer. Methods Fifty-two eyes of 52 pre-LASIK myopic volunteers whose mean age was 21.6±4.8 years， with an average spherical equivalent of -4.8±2.1 D， were enrolled in this prospective study. Corneal refractive power was measured by both the Keratron topographer and the Sirius Scheimpflug-Placido topographer. Keratron measures Km， which is simulated keratometry； Sirius provides two kinds of corneal refractive power： Sim K and mean pupil power （MPE） under different pupil sizes using ray tracing. Three consecutive measurements were obtained. The coefficient of variation and Cronbach′s alpha and intraclass correlation coefficient（ICC） were used to assess the repeatability of the Sim K and MPE obtained by Sirius. The differences between Sim K， MPE and Km were analyzed by a repeated-measures analysis of variance. Pearson correlation and Bland-Altman analysis were used to evaluate the correlation and agreement between Sim K， MPE and Km. Results The results of Km， Sim K， MPE3， MPE4， MPE4.5， MPE5， MPE6 and MPE7 were 42.91±1.52 D，42.25±1.50 D， 42.42±1.52 D， 42.52±1.52 D， 42.63±1.55 D， 42.87±1.57 D， 43.11±1.60 D and 42.99±1.50 D， respectively. The coefficients of variation were lower than 1% for all parameters measured by Sirius. Cronbach′s Alpha and ICC were both higher than 0.99. The Sim K averaged 0.08 D lower than Km with statistically significant differences （t=4.11， P<0.01）. The MPE3 average was 0.74 D smaller than Km with statistically significant differences （t=32.00， P<0.01）. Pearson analysis indicated excellent correlations （r>0.98， P<0.01）. The 95% limits of agreement between Sim K and Km， MPE3 and Km were （-0.35 D， 0.19 D）， （-1.07 D， -0.41 D）. Conclusion In myopic eyes， simulated keratometry measured by Sirius was similar to Keratron. The instruments can be regarded as clinically interchangeable. However， mean pupil power using ray tracing cannot be factored directly into intraocular lens power calculations.
潘超,黄锦海,华焱军,谭维娜,鲁伟聪,王勤美. 新型Scheimpflug眼前节全景仪评估近视患者角膜屈光力的重复性和准确性[J]. 中华眼视光学与视觉科学杂志, 2014, 16(9): 557-561.
Pan Chao,Huang Jinhai,Hua Yanjun,Tan Weina,Lu Weicong,Wang Qinmei. Repeatability and accuracy of the new Scheimpflug-Placido topographer for measuring corneal refractive power in myopic eyes. Chinese Journal of Optometry Ophthalmology and Visual science, 2014, 16(9): 557-561. DOI: 10.3760/cma.j.issn.1674-845X.2014.09.010
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