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Analysis of astigmatism type influence on in vivo corneal biomechanical measurements
Yan Huo1, Qiyu Zhang1, Zhengyuan Qu2
1School of Medicine, Nankai University, Tianjin, China.
Purpose:
This study aimed to evaluate the influence of astigmatism type on in vivo corneal biomechanical measurements and to analyze the correlation using astigmatic power vector components, providing evidence for precise clinical interpretation.
Methods:
This prospective observational comparative study included 155 eyes from 155 participants. Corneal tomographic and biomechanical parameters were obtained using Pentacam and Corvis ST. Participants were classified into four groups according to astigmatism axis and cylinder power: no astigmatism (n = 30), with-the-rule astigmatism (WTR, n = 50), against-the-rule astigmatism (ATR, n = 37), and oblique astigmatism (Oblique, n = 38). Cylinder power and axis were decomposed into Thibos power vector components (J0, J45). Differences in 15 dynamic corneal response (DCR) parameters among the four groups were compared using one-way analysis of covariance (ANCOVA). Partial correlation analysis and multiple linear regression were performed to evaluate the correlations between J0/J45 and DCR parameters after adjusting for confounding factors, followed by within-subgroup analyses.
Results:
After adjustment for intraocular pressure, central corneal thickness, and age, the stiffness parameter SP-A1 differed significantly among the four groups (P = 0.007). The WTR group had higher SP-A1 than the ATR group (mean diff = 4.89 mmHg/mm, P = 0.0284) and the Oblique group (mean diff = 5.32 mmHg/mm, P = 0.0122). Multiple linear regression showed that J0 was independently correlated with Integrated Radius (β = 0.196), HC dArc length (β = 0.223), SP-A1 (β = 0.101), Radius (β = -0.182) and SSI (β = -0.181, all P < 0.05). J45 was independently associated with A1 time (β = -0.033) and A2 velocity (β = -0.156, both P < 0.05).
Conclusion:
In vivo biomechanical measurements were influenced by different astigmatism types. SP-A1 was the primary outcome and differed significantly among astigmatism types. Power vector analysis showed that a greater WTR component was correlated with higher SP-A1, Integrated Radius, and HC dArc length, and lower Radius. Astigmatism axis type and cylinder power could be considered when interpreting in vivo biomechanical measurements to improve the precision of corneal biomechanical evaluation.
