Distribution of Corneal Geometric Landmarks and Relationship Between Their Distances and Biomechanical Parameters in the Development of Keratoconus

Lei Tian; Hui Zhang; Li-Li Guo; Xiao Qin; Di Zhang; Lin Li; Ying Wu; Ying Jie; Haixia Zhang

doi:10.3389/fbioe.2021.766163

Distribution of Corneal Geometric Landmarks and Relationship Between Their Distances and Biomechanical Parameters in the Development of Keratoconus

Front Bioeng Biotechnol. 2021 Dec 22:9:766163. doi: 10.3389/fbioe.2021.766163. eCollection 2021.

Authors

Lei Tian^{1

2}, Hui Zhang^{3

4}, Li-Li Guo⁵, Xiao Qin³, Di Zhang^{3

6}, Lin Li^{3

6}, Ying Wu⁵, Ying Jie¹, Haixia Zhang^{3

6}

Affiliations

¹ Beijing Institute of Ophthalmology, Beijing Tongren Eye Center, Beijing Tongren Hospital, Capital Medical University and Beijing Ophthalmology and Visual Sciences Key Laboratory, Beijing, China.
² Beijing Advanced Innovation Center for Big Data-Based Precision Medicine, Beihang University & Capital Medical University, Beijing, China.
³ School of Biomedical Engineering, Capital Medical University, Beijing, China.
⁴ Department of Medical Engineering, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences, Beijing, China.
⁵ Department of Ophthalmology, Chinese People's Liberation Army General Hospital, Beijing, China.
⁶ The First People's Hospital of Xuzhou, Jiangsu, China.

Abstract

Purpose: To analyze the changes in coordinates and distances among three typical geometric landmarks of the cornea, namely, the thinnest point (TP), maximum curvature (Kmax), and corneal apex (AP) during the development of keratoconus, and explore the potential relationship between these changes and the abnormalities of corneal biomechanics. Methods: Normal eyes (n = 127), clinical keratoconic eyes (CKC, n = 290), and the eyes of forme fruste keratoconus (FFKC, n = 85) were included; among them, the CKC group was classified into four grades based on the Topographic Keratoconus Classification (TKC) provided by Pentacam. A total of 38 Corvis ST output parameters and three distance parameters of three typical landmarks (D_Kmax-AP, D_TP-AP, and D_Kmax-TP) based on Pentacam were included. The differences of parameters among the abovementioned six groups (Normal, FFKC, and CKC stage I to CKC stage IV) were analyzed. Spearman's rank correlation test was performed to choose several dynamic corneal response (DCR) parameters that could best reflect the changes of corneal biomechanical characteristics during the progression of the disease, and the Pearson's or Spearman's correlation test was conducted to determine the association between the three distances and the selected DCR parameters in each grade. In addition, by flipping the X coordinate of the left eye on the vertical axis to reflect the direction of the right eye, the coordinates of TP and Kmax in different developmental grades were highlighted. Results: From CKC stage II, the three geometric landmark distances commenced to correlate with the corneal DCR parameters (CBI, SPA1, IR, DA Ratio 2, ARTh, MIR, Radius, Pachy, and DA Ratio 1), which could better represent the changes of biomechanical properties from normal cornea to keratoconus. From normal cornea to CKC stage IV, the coordinates of Kmax were gradually tended to the inferior temporal region from dispersion, while TP was always concentrated in the inferior temporal region. Although D_Kmax-AP, D_Kmax-TP, and D_TP-AP all showed a gradual decreasing trend with the progress of the disease, the first two did not change significantly, and only D_TP-AP significantly approached AP in the later stage of disease development. In addition, from the FFKC group, the corresponding values of D_Kmax-TP in each disease development group were smaller than D_Kmax-AP. Conclusions: In the later stage of keratoconus, the relationship between the three typical landmark distance parameters and DCR parameters is stronger, and even the weakening of corneal biomechanical properties may be accompanied by the merger of typical landmark positions.

Keywords: biomechanics; forme fruste keratoconus; geometric landmark; keratoconus; morphology.