| Crystal surgery has been one of the refractive surgeries, not only for treating blindness as before. But in the clinical work, there are still some errors existing between postoperative actual refractive state and the predictive value. As the surgical technology has matured, it's considered that such error is mainly caused by the calculation of intraocular degree. The calculating formula has been improved for many years and the accurate intraocular degree depends on the parameters in the formula. The parameters includes the A-constant, axial length and corneal curvature. It is reported that axial length and corneal curvature measurement error account for 53.91% and the axial length measurement error is twice than the corneal curvature measurement error. The longer axial length is, the greater the measurement error will be. So the key point is to reduce axial length measurement error, especially for the patient with high myopia.Objective: In this study, we compared the measurement accuracy of A-scan with IOL-Master in order to analyze the main reason for the measurement error and supply the reference for the clinic, thereby reducing the axial length measurement error.Methods: Collect the document of 68(136 eyes) myopia patients in the out-patient department of our hospital from May,2006 to August,2007. The patients are between 18 and 30, with an average age of 25.6, including 32 male and 36 female. According to the degree of myopia, the cases are divided into four groups. Group A: 30eyes,below moderate myopia (<-3.00 D), Group B: 28eyes, moderate myopia (-3.00D ~ <-6.00D),Group C: 28 eyes,high myopia group (≥-6.00D ~ <-10.00D)and Group D: 50 eyes, super high myopia group (≥-10.00D). In the Group D, some patients are not fit for corneal refractive surgery but they expect to remove the glasses eagerly, so these patients are called D1 group (21 cases 42eyes), who experience the operation of transparent lens cortex aspiration and intraocular lens implantation.Use the Auto kerato-refractometer (Model KR- 8100PA,Japanese Topcon corporation) to measure corneal curvature and A-scan (France QUANTEL MEDICAL companies) and IOL-Master (Germany Zeiss)respectively to measure axial length and then calculate intraocular lens degree, IOL-Master simultaneous measures the corneal curvature.All the intraocular lens degree are calculated by SRK/T formula. The axial length is depended by A-scan, the corneal curvature is depended by kerato-refractometer. All patients are implanted the posterior chamber intraocular lens (PC-IOL),folded Monolithic Rayner.Three months later, patients are given the standard subjective refraction to get the refractive state. The diopter is calculated by the spherical equivalent (the spherical equivalent means the spherical degree add 1/2 column degree).the absolute value of the margin between the subjective refraction degree and the A-scan preoperative reserve degree is considered to be the absolute refractive error value of A-scan group; Similarly, the absolute value of the margin between the subjective refraction degree and the IOL-Master preoperative reserve degree is considered to be the absolute refractive error value of IOL-Master group.Results: In the nearsighted patients with diopter below -10.00D,there is no statistically significance between the A-scan and the IOL-Master measured in the axial length; In group D for the same eye, the value by IOL-Master is longer than contact A-scan, the difference of the axial length by the two methods is between 0.70mm and 0.05mm,with an average of 0.28mm.The difference is significant; The corneal curvature measurement of each group has shown no significant difference by paired t-test. There is no significant difference in axial length of patients with diopter below -10.00D by the two methods and the IOL degree is not different too.The A-scan absolutely refractive error≤±0.50D accounts for 28.57% and the absolute refractive error of IOL-Master≤±0.50D accounts for 30.95%,χ2=0.057,P>0.05. There is no significant difference. The A-scan absolute refractive error≤±1.00D accounts for 73.80%,IOL-Master absolute refractive error≤±1.00D accounts for 76.19%,χ2= 0.063, P>0.05, There is no significant difference, either. These two methods can be considered to have the same effect.Conclusions: 1.In less than -10.00D myopia crowd, there are no difference in axial length by using A-scan and IOL-Master. In ultrahigh myopia crowd, the difference is significant, the measured value of Axial length by IOL-Master is longer than A-scan, with an average of 0.28 mm.2.There is no significant difference in corneal curvature for all patients with myopia measured by kerato-refractometer(Model KR- 8100PA,Japanese Topcon corporation) and IOL-Master.3.Patients who experience the operation of transparent lens cortex aspiration and intraocular lens implantation have postoperative visual acuity improved significantly, though the difference of the axial length by the two methods is significant.4.IOL-Master measurement is accurate in measuring intraocular lens degree.IOL-Master measurement has its own advantages, but it still has certain limitations, which can not completely replace the ultrasound measurement.
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