瞳孔大小和瞳孔中心位移曲线随照明度变化的研究

背景准分子激光角膜屈光手术已成为矫治屈光不正的主要方式之一。术中切削中心的精确定位对术后视觉质量有重要影响。瞳孔中心位置的变化是影响切削中心定位的重要因素，因此有必要对其进行深入研究。目的研究不同照明条件下，人眼瞳孔中心随瞳孔大小改变发生位移过程中的动态规律，探讨瞳孔中心位移曲线的规律在准分子激光角膜屈光手术中的临床应用。方法在Astra Max3D角膜地形图测量系统基础上，对其照明亮度及图像拍摄模式进行自定义修改。利用该系统对57例114眼中度近视患者由照明亮度改变所产生的瞳孔大小和瞳孔中心位置的改变进行测量。照明亮度分为0．8、4．4、18．9、82．3、355．0lx5个光照度等级。使用向量和相对值分析的方法对瞳孔中心相对角膜共轴反光点的位置变化进行统计。不同光照度状态下瞳孔大小的相对变化幅度（AP）以占总变化幅度的百分数（最暗时瞳孔大小的变化设为0％，最亮时变化幅度为100％）表示；瞳孔中心的相对位移量（AC）以占总位移量的百分数（最暗时为0％，最亮时设为100％，以角膜中央顶点为原点）表示，并分析瞳孔中心在随光照度不同而发生变化过程中的位移曲线特点。结果5个光照度水平下瞳孔平均变化量分别为：0、（1．28±0．40）、（2．34±0．53）、（3．34±0．54）、（4．03±0．56）mm。AP分别为0％、32％、58％、83％、100％。随着光照度水平的增加，瞳孔由大变小时，瞳孔的中心位置由角膜顶点的颞侧向鼻侧发生位移。5个光照度情况下瞳孔中心平均位移量分别为：0、（78±33）、（116±60）、（143-±66）、（170±71）μm。AC分别为0％、46％、68％、84％、100％。AC与AP之间存在近似线性关系（r=0．980，P=0．025）；瞳孔中心位移的幅度和瞳孔大小变化幅度呈正相关（r=0．480，P〈0．01）。结论当光照度水平发生变化时，瞳孔中心位置随瞳孔大小变化发生一致性改变，可以用于指导个性化准分子激光角膜屈光手术切削中心的精确定位。

A study on pupillary centroid shift and pupil size under the different illumination levels

Background Excimer laser corneal refractive surgery is one of the major methods to correct refractive error.Centration of the ablation zone is an important factor that affects visual quality after surgery.The pupil center and its shift is a major factor to determine the ablation center.Therefore further study on pupil centroid shift with illumination level alteration is needed.Objective This study aimed to study the characteristics of the pupillary centroid shift along with the change of pupil size under the different illumination conditions and the possible clinical application of the curve of pupillary centroid shift in exeimer laser corneal refractive surgery.MethodsThe variation of pupil size induced by illumination and the changes of pupil center were measured on 114 moderate myopia eyes of 57 subjects with Astra MaxTM Corneal Topographer.Illumination of placido target and image snap model of the topographer was customized to provide 5 illumination levels as follows:0.8,4.4,18.9,82.3,355.0 Lx.Vectorial analysis was used to graph the change of pupil center related to the Coaxially Sighted Corneal Reflex (CSCR).Raw data is converted to relative value to analyze the pupiilary centroid shift.The mean relative change of the pupil size(△P)and the mean of relative pupillary centroid shift(△C)in the form of percentage were used to attenuate the variation among subjects.The original value of illumination(darkest)is defined as 0％ and maximum value(lightest)was as 100％.Results With the increase of illumination,the shift of the pupil center towards nasal side when pupil constrict was found.The mean change of pupil size under the 5 illumination levels were 0,(1.28 +0.40)mm,(2.34 ±0.53)mm,(3.34+0.54)mm,(4.03 ±0.56)mm respectively,and the △P values was 0％,32％,58％,83％,100％ respectively.The mean of pupil centroid shift under the 5 illumination levels were 0,(78±33)μm,(116±60)μm,(143 ±66)μm,(170±71)μm respectively,and the △C was 0％,46％,68％,84％,100％respectively.There was a linear relation between the relative pupil centroid shift and the relative change of pupil size (r=0.980,P=0.025).The amount of pupil centroid shift has a positive correlation with amplitude of the change of pupil size(r=0.480,P＜0.01).Conclusion Pupil center shifts with the change of pupil size.The linear relation between relative pupil centroid shift and the relative change of pupil size can be applied in eximer laser corneal refractive surgery to improve the visual quality with customized ablation center location.