A study on pupillary centroid shift and pupil size under the different illumination levels / 中华实验眼科杂志

ABSTRACT

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 follows0.8,4.4,18.9,82.3,355.0 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.