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 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.
ABSTRACT
Background Nowadays,customized ablation is widely used in the excimer laser corneal refractive Burgery.And the Q-value guide LASIK is one of the research hotspots. Objective Present study was to evaluate and compare the effectiveness of Q-value guide LASIK and standardized LASIK for myopia.Methods A systematic literature retrieval from 2003 through 2010 was conducted in the MEDLINE,CNKI,Cochrane Library,EMBASE.The literature examine possible difierences in uncorrected visual acuity(UCVA),Q-value,higher order aberrations(HOAs),and spherical equivalent(SE) between Q-value guide LASIK and standardized LASIK for correcting myopia.Statistical analysis was performed using a Review Manager 5.0 software.The data was extracted,and the methodological quality was evaluated by two reviewers independently.The quality of included literature was scored according to the Jadad Scale. Results A total of 14 studies involving 1617 patients(2956 eyes)was included in the meta-analysis.Of these fourteen studies,six studies were randomized trials and the other eight studies were retrospective cohort studies.According to the Jadad Scale,2 studies scored 3 points,and the other 12 studies scored 1～2 points.The results showed that the Q-value guide LASIK group had a better postoperative effectiveness in uncorrective visual acuity(UCVA)(WMD=0.04.95% CI 0.00 to 0.08,P<0.05).Q-value(SMD=-1.52,95% CI -2.23 to-0.81,P=0.00),total HOAs (SMD=-1.63,95% CI-2.57 to-0.69,P<0.05) and spherical-like aberrations ( SMD =-1.49,95% CI-2.22 to-0. 76,P<0. 00) after surgery. However, the number of eyes achieved UCVA≥20/20 ( OR= 1.16,95% CI 0. 61 to 2. 19,P=0. 65) ,coma-like aberrations (SMD=-1. 02,95% CI-0. 36to 0.11,P=0.29) and SE (WMD=0.10,95% CI-0.11 to 0.31,P=0.34) after surgery were comparable.Conclusion The effectiveness of Q-value guide LASIK is superior to standardized LASIK for treatment of myopia.High-quality clinical randomized-controlled study should be performed to further evaluate the comparable outcome of Q-value guide LASIK with standard LASIK.
ABSTRACT
Background Recently,whether the epithelial flaps should be removed or preserved during the Epi-LASIK and its affection on clinical results are concerned.Objecfive This system analysis was to evaluate and compare the clinical effectiveness between on-flap Epi-LASIK and off-flap epi-LASIK for myopia. Methods A systematic literature retfieval was conducted in the MEDLINE,EMBase,Coehrane Library,CBM disc,CNKI from 2003 through 2009.The possible differences in reepithelization time,pain sensation,and haze after surgery were compared between on-flap and off-flap Epi-LASIK for myopia.The statistical analysis was performed using a RevMan 4.2 software.The data was extracted,and the methodological quality was evaluated by two reviewers independently with weighted mean difierence(WMD)for the effectiveness analysis and odds ratio(OR)for counting variable.The quality of included literature was scored according to the Jadad Scale. Results A total of 8 studies involving 251 patients(502 eyes)were included in the meta-analysis.Of these eight studies.five studies were randomized clinical trials and the other three studies were retrospective cohort studies.Compared with on-flap Epi-LASIK group,off-flap Epi-LASIK group had a better postoperative outcome in the mean reepithelization time(WMD=1.32,95％CI-1.82to-0.82,P<0.01)and pain scores at 3,5 day(WMD=-O.99,95％CI-1.71 to-0.28,P(0.01)(WMD=-0.94.95％CI-1.35 to-0.54,P<0.01)after surgery.No significant difierenees were found in the eye numbers of haze at 1 month(OR=0.62,95％C1 0.34 to 1.12,P=0.11),3 months(OR=0.70,95％C1 0.31 to 1.55,P=0.38)and 6 months(OR=1.14,95％C1 0.58 to 2.26,P=0.71)between these two types of operation.The pain scores at the first day after surgery was not significantly different between these two groups(WMD=-0.17,95％CI -0.55 to 0.20,P=0.37). Conclusion The effectiveness of off-flap Epi-LASIK is superior to on-flap Epi-LASIK for myopia.Some high-quality randomlizd and control studies are needed for the further clinical evaluation.