[Study on corneal biomechanical properties of suspicious keratoconus patients in corneal topography]

Objective: To explore the characteristics and significance of corneal biomechanics in patients with suspicious total deviation value in Belin/Ambrosio Enhanced Ectasia Display of Pentacam corneal topography. Methods: In this cross-sectional study, 206 patients (325 eyes) with myopia or myopic astigmatism were collected from refractive surgery center of Tianjin Eye Hospital. Among them, 110 males(213 eyes) and 96 females (153 eyes) were aged (22.68±5.20) years. 57 patients (71 eyes) with a total deviation value of 1.6-3.0 in the Pentacam corneal topography were included in the suspicious group, and 149 patients (254 eyes) of<1.6 were included in the control group. The values of the first applanation time (A1-Time), first applanation length (A1-Length), first applanation velocity (A1-Velocity), second applanation time (A2-Time), second applanation length (A2-Length), second applanation velocity(A2-Velocity), highest concavity time (HC-time), highest concavity deformation amplitude (DA), highest concavity peak distance (PD), highest concavity radius (HC-Radius, RoC), intraocular pressure were measured using the corneal visualization Scheimpflug technology. The total deviation value in Belin/Ambrosio Enhanced Ectasia Display were measured with a Pentacam. The biomechanical parameters of the suspicious group were compared with the normal group by the two independent samples t test and the identity regression analyses. The data correlation was performed using Pearson linear correlation analysis. Results: Compared with the D normal group, the K1, K2 and Km of D suspicious group were significantly increased (P<0.001). A1-Velocity [(0.152±0.015) m/s] and DA[(1.050±0.090) mm] were significantly increased (t=4.348, 2.708; P<0.001, 0.007), while the CCT, A1-Length, A2-Length and RoC were significantly decreased (P<0.01) in suspicious group. In suspicious group, there was a significant correlation between A1-Time, A1-Length, A2-Length, A2-Velocity, IOP and CCT(r=0.305, 0.324, 0.238, 0.346, 0.316; P<0.05). There was a significant correlation between the anterior surface refractive power K1 and the A1-Length (r=-0.361, P=0.002), and there was a significant correlation between the A1-Length, RoC and anterior surface refractive power K2 (r=-0.369, -0.242; P=0.002, 0.043). There was a significant correlation between anterior surface refractive power Km and A1-Length (r=-0.373, P=0.001). After adjusting the confounding factors between two groups by the identity regression analyses, the A1-Length (P=0.003), A1-Velocity (P<0.001) and DA (P=0.002) were still significant differences. Conclusions: In total deviation value suspicious group, the corneal thickness was thinner, corneal curvature became steeper and the corneal biomechanical properties were weaker. It is important to screen keratoconus before corneal refractive surgery and choose a reasonable surgical procedure to reduce corneal dilatation after refractive surgery. (Chin J Ophthalmol,2019, 55: 442-447).