The iris is a muscular organ whose deformations can cause primary angle-closure glaucoma (PACG), a leading cause of blindness. PACG risk assessment does not consider iridial biomechanical factors, despite their expected influence on iris deformations. Here we exploited an existing biometric data set consisting of near-infrared movies acquired during the pupillary light reflex (PLR) as a unique resource to study iris biomechanics. The PLR caused significant (>100%) and essentially spatially uniform radial strains in the iris in vivo, consistent with previous findings. Inverse finite element modeling showed that sphincter muscle tractions were c. 5-fold greater than iridial stroma stiffness (range 4- to 13-fold, depending on sphincter muscle size). This muscle traction is greater than has been previously estimated, which may be due to methodological differences and/or to different patient populations in our study (European descent) vs. previous studies (Asian); the latter possibility is of particular interest due to differential incidence rates of PACG in these populations. Our methodology is fast and inexpensive and may be a useful tool in understanding biomechanical factors contributing to PACG.

中文翻译：

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人眼虹膜变形和肌肉收缩的体内生物力学评估

虹膜是一种肌肉器官，其变形会导致原发性闭角型青光眼 (PACG)，这是导致失明的主要原因。PACG 风险评估不考虑虹膜生物力学因素，尽管它们对虹膜变形的预期影响。在这里，我们利用现有的生物特征数据集，其中包括在瞳孔光反射 (PLR) 期间获得的近红外电影，作为研究虹膜生物力学的独特资源。PLR在体内虹膜中引起显着（> 100％）和基本空间均匀的径向应变，与之前的发现一致。逆有限元模型显示括约肌牵引力为 c。比虹膜间质硬度高 5 倍（范围为 4 至 13 倍，取决于括约肌大小）。这种肌肉牵引力比以前估计的要大，这可能是由于我们的研究（欧洲血统）与以前的研究（亚洲）中的方法学差异和/或不同的患者群体；由于这些人群中 PACG 的发病率不同，后一种可能性特别令人感兴趣。我们的方法既快速又便宜，可能是了解促成 PACG 的生物力学因素的有用工具。