[Analysis of distribution characteristics and influencing factors of chord μ in young myopia].

Objective: To explore and analyze the distribution characteristics of chord μ related parameters, as well as the pupil center's relative position to the coaxial corneal light reflex on the corneal surface, and the influencing factors in young myopia. Methods: This was a cross-sectional study. A total of 761 myopic patients (761 eyes) were collected from March 2021 to December 2021 in the Refractive Surgery Center of Tianjin Eye Hospital, including 388 males and 373 females, with an average age of (24±6) years. The relationship between age, sex, diopter, anterior and posterior corneal surface parameters, and chord μ related parameters was analyzed, including the x and y absolute values of the pupil center, chord μ length, and angle. The normality of the data was tested using the Kolmogorov-Smirnov test, and the influencing factors of chord μ were analyzed through Pearson and Spearman correlation analysis. Results: The equivalent spherical degree and chord μ length were (-5.47±1.66) D and (0.178±0.095) mm, respectively. The chord μ length followed an approximately normal distribution. The chord μ length of 266 eyes (35%) was distributed in the range of 0.120 to 0.200 mm, while the chord μ length of 479 eyes (63%) was<0.200 mm, and the chord μ length of 620 eyes (81%) was<0.260 mm. The chord μ angle distribution accounted for the largest proportion in the superior nasal quadrant (45.6%), followed by the superior temporal quadrant (34.3%), the inferior temporal quadrant (10.1%), and the inferior nasal quadrant (10.0%). High myopia (r=0.11, P=0.002) and high astigmatism (r=0.08, P=0.023) were associated with an increase in chord μ length. The higher the degree of myopia, the smaller the chord μ angle (r=-0.09, P=0.019). The larger the ISV (r=0.09, P=0.017), IVA (r=0.08, P=0.025), and IHD (r=0.08, P=0.039) on the anterior surface of the cornea, the longer the chord μ length. The higher the astigmatism of the posterior corneal surface, the greater the absolute value of the Y coordinate of the pupil center (r=0.07, P=0.044), and the longer the chord μ length (r=0.08, P=0.035), and the smaller the chord μ angle (r=-0.08, P=0.032). Conclusions: The chord μ length of young myopic individuals in China followed an approximately normal distribution, with the majority located in the superior nasal and superior temporal quadrants. High myopia, high astigmatism, and irregular corneal shape are the main factors related to an increase in chord μ length.目的： 探讨我国青年近视眼人群μ弦（瞳孔中心相对于角膜共轴反光点在角膜表面的二维位移）参数的分布特点及相关因素。 方法： 横断面研究。收集2020年3至12月在天津市眼科医院屈光手术中心就诊的近视患者761例（761只眼），其中男性388例，女性373例，年龄（24±6）岁。分析年龄、性别、屈光度数，应用Pentacam眼前节分析仪收集患眼的中央角膜厚度、角膜前后表面散光度、表示前表面曲率差异的角膜表面不规则指数（ISV）、垂直对称指数（IVA）、高度偏心指数（IHD），并分析这些参数与μ弦参数的关系，包括瞳孔中心的坐标和μ弦的长度及角度。对μ弦的影响因素进行相关性分析。 结果： 761只眼的等效球镜度数为（-5.47±1.66）D，μ弦长度为（0.178±0.095）mm。μ弦长度呈近似正态分布，266只眼（35%）的μ弦长度分布在0.120~0.200 mm，479眼（63%）的μ弦长度<0.200 mm，620只眼（81%）的μ弦长度<0.260 mm。μ弦的角度分布以鼻上象限（45.6%）所占比例最大，其次为颞上象限（34.3%），颞下象限（10.1%）和鼻下象限（10.0%）。高度近视眼（r=0.11，P=0.002）和高度散光（r=0.08，P=0.023）与μ弦长度显著相关，近视度数越高，μ弦角度越小（r=-0.09，P=0.019）。角膜前表面ISV（r=0.09，P=0.017）、IVA（r=0.08，P=0.025）、IHD（r=0.08，P=0.039）越大，μ弦长度越大。角膜后表面散光度数越高，μ弦长度（r=0.08，P=0.035）、瞳孔中心的y轴坐标绝对值（r=0.07，P=0.044）越大，μ弦角度越小（r=-0.08，P=0.032）。 结论： 我国青年近视眼人群μ弦长度呈近似正态分布，位置分布以鼻上及颞上象限居多。高度近视眼、高度散光与角膜形态不规则是μ弦长度增大的主要相关因素。.