浸润式A型超声法与Lenstar光学生物测量仪在不同类型白内障眼测量的晶状体厚度值的差异及其临床意义

The difference of lens thickness measured by immersion A-scan ultrasound versus Lenstar optical biometry in various types of cataract eyes and its clinical significance

背景白内障是全球致盲眼病的主要原因，手术是目前治疗白内障的主要手段，因此术前参数的精准测量对提高术后视觉质量有重要意义。目的比较浸润式A型超声与Lenstar光学生物测量仪对不同类型白内障晶状体厚度（LT）进行测量时结果的差异，分析两种检测方法的一致性，探讨超声测量在对不同类型和不同核硬度的白内障患者进行LT测量时是否需要改变声速参数。方法采用诊断试验可靠性评价方法，分别应用浸润式A型超声和Lenstar光学生物测量仪（Lenstar测量仪）于2013年9月至2014年5月在天津市眼科医院对130例143眼单纯白内障患者进行LT测量，按照白内障类型不同分为核性白内障组50例60眼、后囊下性白内障组40例40眼和皮质性白内障组43例43眼；核性白内障组患眼根据Emery核硬度分级标准亚分为Ⅱ级核白内障14例20眼、Ⅲ级核白内障17例20眼和Ⅳ级核白内障19例20眼，采用配对t检验法对2种方法测量的LT值的差异进行比较；采用Bland—Altman图对2种测量方法的测量值进行一致性分析。结果浸润式A型超声法对核性白内障眼测量的LT值为（4．85±0．39）mm，明显高于Lenstar测量仪的测量值（4．74±0．37）mm，差异有统计学意义（t=3．020，P=0．004），2种测量方法间对后囊下性白内障眼和皮质性白内障眼测量的LT值差异均无统计学意义（t=1．015，P=0．316；t=1．275，P=0．209）。浸润式A型超声法对Ⅱ、Ⅲ、Ⅳ级核白内障患者测量的LT值均明显高于Lenstar测量仪的测量值，差异均有统计学意义（t=2．175、2．378、2．383，均P〈0．05）。浸润式A型超声法与Lenstar测量仪在后囊下性白内障眼测得的LT值一致性较好，95％一致性界限（LoA）为-0．21-0．18mm，而在核性白内障眼和皮质性白内障眼中2种测量方法测得的LT值一致性较差，95％LoA分别为-0．64-0．43mm和-0．50-0．41mm。浸润式A型超声与Lenstar测量仪在Ⅱ、Ⅲ、Ⅳ级核白内障眼测得的LT值一致性均较差，95％一致性界限分别为-0．31-0．22mm、-0．32-0．24mm和-1．09-0．62mm。结论浸润式A型超声法与Lenstar测量仪在测量不同类型白内障的LT值时存在一定差异，浸润式A型超声法测量值较高，提示浸润式A型超声法测量不同类型白内障LT时不能简单地使用统一的平均声速参数，采用浸润式A型超声对具有不同核硬度的核性白内障患者进行LT测量时也应当考虑改变声速参数。

Background Cataract is the main cause of global blindness,and surgery is the main method for the treatment of cataract, so precise preoperative parameters have an important significance for improving postoperative visual quality. Objective This study was to analyze the difference of lens thickness （LT） measured by immersion A-scan ultrasound versus optical biometry and consistency of these two methods in measuring the LT for different types of cataract eyes,and to investigate whether A-scan ultrasound for the LT measurement needs to correct the ultrasound speed parameter. Methods A reliability evaluation of diagnosis test was designed. The LT was measured on 143 cataract eyes using immersion A-scan ultrasound and Lenstar optical biometry in Tianjin Eye Hospital from September 2013 to May 2014. The eyes were assigned to nuclear cataract group （60 eyes of 50 patients） , posterior subcapsular cataract group （40 eyes of 40 patients） and cortical cataract group （43 eyes of 43 patients） based on the types of cataract,and the hardness of nucleus was grade 11 in 20 eyes of 14 patients,grade m in 20 eyes of 17 patients and grade IV in 20 eyes of 19 patients. The outcomes measured by immersion A-scan ultrasound versus Lenstar optical biometry were compared with paired t test, and the consistency between the two devices was analyzed by Bland-Altman agreement plot. This study complied with Helsinki declaration, and written informed consent was obtained from each patient prior to any examination. Results The mean LT value was （4.85± 0. 39）mm from the immersion A-scan ultrasound and （4. 74 ±0. 37） mm from the Lenstar optical biometry, with a significant difference between the two devices （ t = 3. 020, P = 0. 004）. No significant differences were found in the LT values of the posterior subcapsular cataractous eyes and cortical cataractous eyes between the two devices （ t = 1.015 ,P = 0.316 ; t = 1. 275, P = 0. 209 ）. The LT values by immersion A-scan ultrasound were significantly higher in grade II , III and IV nuclear cataractous eyes than those by Lenstar optical biometry （t = 2. 175,2. 378,2. 383, all at P〈0.05 ）. The outcome showed a good consistency in the posterior subcapsular cataractous eyes between the two measuring methods,with the 95% limitation of agreement （LoA） from -0. 21 to 0.18 mm. However, there were poor consistencies between the two measuring methods in the nuclear and cortical cataractous eyes,with the 95% LoA from -0. 64 to 0.43 mm and from -0. 50 to 0.41 mm,respectively. Poor consistencies also were seen in grade II, III, IV nuclear cataractous eyes between the two measuring methods, and the 95% LoA were -0.31 to 0.22 mm,-0.32 to 0.24mm and -1.09 to 0.62 mm, respectively. Conclusions There are differences in measuring LT of different types of cataractous eyes between immersion A-scan ultrasound and Lenstar optical biometry. The measuring values are higher by immersion A-scan ultrasound than those by Lenstar optical biometry, suggesting that the measurement of immersion A-scan ultrasound for LT of different types and nuclear hardness of cataractous eyes should correct the ultrasound speed parameters.