Bruner Cameron D, Mahmoud Ashraf M, Roberts Cynthia J
Ophthalmology & Visual Sciences, College of Medicine, The Ohio State University Wexner Medical Center, Columbus, Ohio.
Biomedical Engineering, College of Engineering, The Ohio State University, Columbus, Ohio.
Ophthalmol Sci. 2024 Dec 20;5(3):100682. doi: 10.1016/j.xops.2024.100682. eCollection 2025 May-Jun.
To investigate the difference in biomechanical response metrics between central and eccentric pathology and compare axial vs. tangential curvature, as well as zonal vs. single-point values.
Prospective, observational, cross-sectional study.
The study included 67 eyes of 41 subjects diagnosed with keratoconus (KCN).
Pentacam tomography and Corvis ST examinations were acquired, and disease severity was defined by maximum curvature, comparing single point of maximum anterior axial curvature (Kmax) vs. magnitude of surrounding 2 mm zonal value (ZKmax) on axial maps, vs. magnitude of steepest 2 mm zone on axial (CSpot_Axi) and tangential (CSpot_Tan) maps located by Cone Location and Magnitude Index (CLMI). Distance between the corneal center and Kmax (Kmax_dist) was compared to radial distance with CLMI (CRad_Axi and CRad_Tan). Single-point Kmax, ZKmax, and CLMI-derived zones were compared with biomechanical metrics via regression analyses, including stiffness parameter at first applanation (SP-A1), deformation amplitude ratio at 2 mm (DA Ratio), integrated inverse radius (IIR), and stress-strain index (SSI). Measurements were analyzed using paired tests, with tests between central and eccentric disease, and a significance threshold, < 0.05.
Maximum curvature using axial vs. tangential curvature, zonal vs. single-point curvature, and corneal stiffness metrics compared with cone location.
Significantly greater central pathology was found using tangential (58 central and 9 eccentric) vs. axial curvature (28 central and 39 eccentric). ZKmax was significantly different than CSpot_Axi and CSpot_Tan ( < 0.0001). CRad_Axi (1.53 ± 0.41 mm) was significantly greater ( < 0.001) than Kmax_dist (1.33 ± 0.56 mm) and CRad_Tan (0.99 ± 0.34 mm). Kmax (56.09 ± 8.99 diopter [D]) was significantly greater than ZKmax (51.81 ± 7.50 D). Regressions for ZKmax, CSpot_Axi, and CSpot_Tan were significantly negative to SP-A1, stiffness parameter at highest concavity, and SSI, whereas significantly positive to DA Ratio and IIR. Regressions for Kmax_dist, CRad_Axi, and CRad_Tan had significantly positive relationships to SSI and significantly negative relationships to DA Ratio and IIR.
Central pathology has greater frequency with tangential than axial curvature. Corneal stiffness increases as the distance of the cone from the center increases, consistent with the focal nature of KCN. Central stiffness decreases as cone curvature (disease severity) increases. Recommendation is to use zonal values with tangential curvature to evaluate the location of the greatest curvature and changes in curvature over time.
Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.
研究中央病变与偏心病变在生物力学反应指标上的差异，并比较轴向曲率与切向曲率，以及区域值与单点值。
前瞻性、观察性横断面研究。
该研究纳入了41例被诊断为圆锥角膜（KCN）的受试者的67只眼睛。
进行Pentacam断层扫描和Corvis ST检查，并通过最大曲率定义疾病严重程度，比较轴向图上最大前轴向曲率的单点值（Kmax）与周围2 mm区域值（ZKmax）的大小，以及通过圆锥位置和大小指数（CLMI）定位的轴向（CSpot_Axi）和切向（CSpot_Tan）图上最陡2 mm区域的大小。将角膜中心与Kmax之间的距离（Kmax_dist）与CLMI的径向距离（CRad_Axi和CRad_Tan）进行比较。通过回归分析将单点Kmax、ZKmax和CLMI衍生区域与生物力学指标进行比较，包括首次压平的刚度参数（SP-A1）、2 mm处的变形幅度比（DA Ratio）、积分逆半径（IIR）和应力应变指数（SSI）。测量值采用配对检验进行分析，对中央病变与偏心病变进行检验，显著性阈值P<0.05。
使用轴向曲率与切向曲率、区域曲率与单点曲率以及与圆锥位置相关的角膜刚度指标的最大曲率。
与轴向曲率（28例中央病变和39例偏心病变）相比，使用切向曲率（58例中央病变和9例偏心病变）发现中央病变的频率显著更高。ZKmax与CSpot_Axi和CSpot_Tan显著不同（P<0.0001）。CRad_Axi（1.53±0.41 mm）显著大于Kmax_dist（1.33±0.56 mm）和CRad_Tan（0.99±0.34 mm）（P<0.001）。Kmax（56.09±8.99屈光度[D]）显著大于ZKmax（51.81±7.50 D）。ZKmax、CSpot_Axi和CSpot_Tan的回归与SP-A1、最高凹度处的刚度参数和SSI显著负相关，而与DA Ratio和IIR显著正相关。Kmax_dist、CRad_Axi和CRad_Tan的回归与SSI显著正相关，与DA Ratio和IIR显著负相关。
中央病变在切向曲率中比在轴向曲率中出现的频率更高。随着圆锥与中心距离的增加，角膜刚度增加，这与KCN的病灶性质一致。随着圆锥曲率（疾病严重程度）增加，中央刚度降低。建议使用切向曲率的区域值来评估最大曲率的位置以及曲率随时间的变化。
在本文末尾的脚注和披露中可能会发现专有或商业披露信息。
