Comparison of Two Scheimpflug Systems in the Measurements of Eyes with Corneal Diameter Smaller than 11.1 mm

INTRODUCTION: This article aimed to evaluate the measurements of ectasia parameters by two Scheimpflug-based tomography devices, Pentacam and Sirius, for eyes with different corneal diameters (CDs). METHODS: This cross-sectional research included subjects from the Fudan University EENT Hospital Refractive Center Database that were followed once a year for at least 3 years with unremarkable slit-lamp examination and normal topography. Pentacam and Sirius examinations were performed on these subjects and the ectasia indices were compared between different CD groups. RESULTS: The right eyes of 153 subjects were included (CD ≤ 11.1 mm, n = 50; 11.2–12 mm, n = 52; > 12.0 mm, n = 51). For the ectasia parameters from Pentacam, CD had the greatest influence on the deviation of normality of back elevation (Db, R(2) = 0.371, β = − 1.119, P < 0.001), overall deviation of normality (BAD-D, R(2) = 0.305, β = − 0.589, P < 0.001), and minimum pachymetric progression index (PPImin, R(2) = 0.282, β = − 0.131, P < 0.001). For parameters derived from Sirius, CD had the greatest influence on Baiocchi–Calossi–Versaci index of the back surface (BCVb, R(2) = 0.138, β = − 0.179, P < 0.001), keratoconus vertex of the back surface (KVb, R(2) = 0.099, β = − 2.273, P < 0.001), and BCV (R(2) = 0.071, β = − 0.078, P = 0.001). CD had little influence on surface asymmetry index of the front (SIf) and back surface (SIb), keratoconus vertex of the front surface (KVf), Baiocchi–Calossi–Versaci index of the front surface (BCVf), and Sirius classifier (P > 0.05). CONCLUSIONS: For Pentacam, CD mainly influenced indices related to back elevation (BE) and pachymetry progression, whereas for Sirius, CD mainly influenced indices related to BE and corneal aberration.