Analysis on the role of Sirius combined topography and tomography system in screening for suspect keratoconus

Abstract

Objective: To evaluate the role of Sirius combined topography and tomography system in screening for suspect keratoconus among the corneal refractive surgery candidates. Methods: Retrospective case series study. Eight hundred and sixteen consecutive ametropic patients (1 632 eyes) who underwent routine examinations before corneal refractive surgery at Peking University Third Hospital from January 2016 to September 2016 were reviewed. All the cases were analyzed with Sirius combined topography and tomography system. Fifty-nine eyes of 37 patients, aged (28.9±7.4) years, classified as suspect keratoconus by the system were enrolled in the suspect group, including 25 females (40 eyes) and 12 males (19 eyes). A random eye of the first 59 patients, aged (27.1±6.4)years, whose both eyes were classified as normal by Sirius system were enrolled in the control group, including 38 females and 21 males. The corneal anterior surface, posterior surface and minimum thickness data of the suspect group were analyzed and then compared with the control group. The classified results were further verified by Pentacam system. Independent-samples t test and Mann-Whitney U test were applied to analyze the normal distribution and non-normal distribution data respectively. Results: The medians of anterior surface and posterior surface symmetry index and Baiocchi Calossi Versaci index of anterior surface and posterior surface of the suspect group were 0.84, 0.22, 0.58 and 0.51 D, and that of the control group were 0.05, 0.04, 0.09 and 0.06 D, and the differences were of statistical significance (Z=-18.764, -8.351, -12.248, -10.709, P<0.01). Mean corneal minimum thickness data of the suspect group were (504.4±30.0)μm, and that of the control group were (541.2±32.1)μm, the differences were of statistical significance (t=-6.408, P<0.01). In the suspect group, the eyes related with suspect or abnormal corneal anterior indices accounted for 47.5% (28/59), the eyes related with suspect or abnormal corneal posterior indices accounted for 55.9% (33/59), and the eyes related with suspect or abnormal corneal minimum thickness accounted for 40.7% (24/59). In the suspect group, 45 eyes (76.3%) were classified as suspect or abnormal according to the overall variance index "D" by Belin-Ambrósio Display (BAD) of the Pentacam system, and the other 14 eyes exhibited at least one abnormal index related with keratoconus. Conclusions: Sirius 3D combined topography and tomography and its integral automatic classification system is capable to screen out the suspect keratoconus simply and effectively. These indices maybe arranged in descending order in terms of the sensitivity as corneal posterior surface, followed by corneal anterior surface and then corneal thinnest point thickness. (Chin J Ophthalmol, 2018, 54: 33-38).