Guo Ji-Xi, Li Xue-Feng, Wang Xin-Chao, Zhao Xin-Heng, Wang Yan, Fang Li-Hua
Key Laboratory for Optoelectronic Information Perception and Instrumentation of Jiangxi Province, Nanchang Hangkong University, Nanchang 330063, Jiangxi Province, China.
Tianjin Key Lab of Ophthalmology and Visual Science, Tianjin Eye Institute, Tianjin Eye Hospital; Nankai University Eye Institute, Nankai University; Clinical College of Ophthalmology, Tianjin Medical University, Tianjin 300000, China.
Int J Ophthalmol. 2025 May 18;18(5):889-896. doi: 10.18240/ijo.2025.05.15. eCollection 2025.
To investigate the effect of the percent tissue altered (PTA) on the safety after laser-assisted keratomileusis (LASIK) based on linear creep characteristics.
The linear creep characteristics of the cornea were characterized by the generalized Kelvin-Voigt constitutive relationship with five parameters. Then, the displacement and stress distribution on the anterior and posterior surfaces of the cornea were analyzed by constructing the eye model with different PTA.
When PTA was above 39%, the vertex displacements under physiological intraocular pressure (IOP, 15 mm Hg) exceeded that of the preoperative glaucoma under average IOP. That is, an excessively high displacement value was found. In addition, with the increase of PTA, the central cornea was stretched thinner and more obviously due to IOP. When PTA was above 39%, the stress at the center of the anterior surface of the residual stroma was more than 20% larger than that of the normal human eye. The residual stroma was forced to stretch more severely due to excessive stress on the anterior surface. This resulted in deformation of the stroma and induced corneal ectasia. Meanwhile, the postoperative vertex displacement increased with the decrease in viscosity ratio.
PTA less than 39% is the safe range for LASIK surgery. This study may provide a reliable numerical basis for postoperative corneal dilatation and the outcomes after refractive surgery.
基于线性蠕变特性研究组织改变百分比（PTA）对准分子激光原位角膜磨镶术（LASIK）后安全性的影响。
采用具有五个参数的广义开尔文-沃伊特本构关系来表征角膜的线性蠕变特性。然后，通过构建不同PTA的眼模型，分析角膜前后表面的位移和应力分布。
当PTA高于39%时，生理眼压（IOP，15 mmHg）下的顶点位移超过了术前青光眼在平均眼压下的顶点位移。也就是说，发现了过高的位移值。此外，随着PTA的增加，由于眼压作用，中央角膜被拉伸得更薄且更明显。当PTA高于39%时，残余基质前表面中心的应力比正常人眼的应力大20%以上。由于前表面的过度应力，残余基质被迫更严重地拉伸。这导致基质变形并诱发角膜扩张。同时，术后顶点位移随着黏度比的降低而增加。
PTA小于39%是LASIK手术的安全范围。本研究可能为屈光手术后角膜扩张及手术效果提供可靠的数值依据。
