白内障术后后囊膜混浊的量化分析
发表时间：2011-11-16 浏览次数：591次
作者：丁衍,柳林,赵世红 作者单位：200433 中国上海市,第二军医大学附属长海医院眼科
【摘要】 目的：评估白内障术后疏水性丙烯酸人工晶状体Sensar AR40e和硅胶人工晶状体的后囊膜混浊(PCO)，并用能客观评估PCO的软件量化分析。方法：共选择98眼行标准的超声乳化白内障吸除术，人工晶状体囊袋内固定。所有眼随机植入Sensar AR40e或硅胶人工晶状体，但同一患者植入的人工晶状体必须不同。在第1～2a时后照法拍摄后囊膜图像，通过去除浦肯野反光、增强对比度、过滤后增强低密度的PCO等方法处理后用POCO软件分析对比。结果：术后1a疏水性丙烯酸人工晶状体PCO百分比为0.32±0.13，硅胶人工晶状体为0.39±0.17(P=0.37)。2a时疏水性丙烯酸人工晶状体PCO百分比为0.42±0.20，硅胶晶状体为0.34±0.18(P=0.50)。患者术后1，2a时疏水性丙烯酸人工晶状体PCO的严重级别分别是0.50±0.30和0.82±0.58，与硅胶人工晶状体的0.63±0.35和0.55±0.35相比，无统计学意义(P=0.52,P=0.69)。结论：POCO后囊膜混浊量化分析系统提供了客观而且可重复性强的量化PCO的方法，也是研究预防PCO技术的有力工具。
【关键词】 后囊膜混浊;量化;丙烯酸;人工晶状体
Abstract
AIM: To evaluate posterior capsular opacification (PCO) with hydrophobic acrylic intraocular lens (IOL, Sensar AR40e) and silicone IOLs after cataract surgery, to use a software program developed to provide an objective assessment of the amount of PCO in the digital images of the posterior capsule to quantify PCO.
METHODS: Ninetyeight eyes underwent standardized phacoemulsification and "in the bag" IOL placement, were randomized to receive a three piece lens of hydrophobic acrylic or silicone, but lens materials were different in one case. In year 1 and 2, digitized retroillumination images were taken from the posterior capsule. Images were analyzed by POCO software program, removing the Purkinje light reflexes, contrast enhancement, filtering to enhance lowdensity PCO.
RESULTS: The percentage of PCO were 0.32±0.13 of hydrophobic acrylic IOLs in year 1, compared with 0.39±0.17 of silicone (P=0.37). In year 2, the percentage of PCO were 0.42±0.20 with hydrophobic acrylic IOLs and 0.34±0.18 with silicone IOLs (P=0.50). Of those patients with PCO in year 1 and 2, severity grades were 0.50±0.30 and 0.82±0.58 of hydrophobic acrylic cases, compared with 0.63±0.35 and 0.55±0.35 of patients with silicone IOLs (P=0.52,P=0.69) with no statistical significance.
CONCLUSION: The POCO system is capable of producing an objective and repeatable measure of PCO that is relevant to assessing techniques of PCO prevention.
KEYWORDS:posterior capsular opacification;quantification; acrylate; intraocular lens
INTRODUCTION
Posterior capsular opacification (PCO) is a common complication after cataract surgery in modern times. According to previous reports, the incidence of PCO of the first 5 years after cataract operation is 3%50%, in which the different frequencies must have some relationship with the different observation evaluation systems. Clinically, the evaluation of PCO mainly depends on the examiners rich clinical experience, but it can only determine the nature rather than the quantity. With digital photographic image acquisition systems, we evaluated PCO with the new hydrophobic acrylic intraocular lens (IOL, Sensar AR40e) and silicone IOLs after cataract surgery. At the same time, we adopted the software [the posterior capsule opacity (POCO) software system] to make quantification and comparison so that we might minimize observation bias and enhance accuracy as well.
MATERIALS AND METHODS
Patients were recruited in a continuous cohort following approval from the hospital ethics committee. We chose as the object of our study the patients who were hospitalized and had their operation for cataract in our hospital from October 2006 to September 2007. The 49 cases (98 eyes) in all were chosen as samples, in which 19 cases (38 eyes) were male, 30 cases (60 eyes) were female. The patients age ranged from 23 to 86 years and the average age was 71.5 years. The preoperative visual acuity was 0.05 0.6. The average time of follow up was 23.4±0.9 months. The classification of lens nucleus was strictly carried out according to LOCSⅡ standard, 21 eyes for Grade N1, 65 eyes for Grade N2 and 12 eyes for Grade N3. In the process of the surgery with the employment of a random table the order of operation for every patient’s two eyes was randomized with controlled blinded trials. For each patient one eye was implanted with Sensar AR40e, and the other with AQ110NV (28 eyes) or SI40NB (21 eyes) silicone IOL. All the surgery was performed between October 2006 and September 2007 by a single surgeon, in the course of which there were some minor accidents, such as capsulorhexis rim tear, failure to place the IOL into the capsular bag, posterior capsules rupture and vitreous loss. All the evaluation and observation of quantifying the postoperative PCO was completed by the same person.
Photography and Analysis of the PCO Images When the pupils of all the patients eyes were fully dilated at year 1 or year 2 of their follow up, we began to take digital standard lens images of the posterior capsule (1024×768 resolutions, every resolution contains 8 digits with the useful information of about 15000 resolutions/mm2) by means of retroilluminated photography with KYF55BE camera of JVC of the digitized image processing system equipped with a slit lamp (DIGEYE) made by Shanghai Yide Medical Equipment Company Ltd. And then we fed the images into the computer and analyzed with the software system of POCO.
Introduction to the Analysis and the Processing of Software All the images were analyzed after they were processed in the same following steps. From ACD see 3.2 the images in the software processing system were enlarged to such a size corresponding to the size of 1328×988mm on the displaying screen, removing the Purkinje light reflexes, enhancing contrast, filtering, and dividing veins. So far the work of images processing has come to an end.
Analysis Software The area we analyzed was an optical area where the posterior capsule hadnt been covered by the anterior capsule. It is called "analytical area". The size of the area was calculated automatically by the software. If the rim of the capsulorhexis tear of the anterior capsule was away from the front surface of IOL, then the rim of IOL would be taken for the analytical area. It was gridpatterned after the analytical area was marked with the mouse. PCO with over 50% grids was marked with blue, yellow or red (which stood for the degree of lightness, fairness and seriousness separately. If needed, there were some reference images for comparison in the software.) Finally dealing with the intergrowth matrix corresponding to the original images we transferred the binary images in the PCO area into the percentage of PCO. Judging from the location and degree of seriousness of PCO, we obtained different serious grades of PCO by calculation [serious grade=3 number of red grids+2 number of yellow grids +1 number of blue grids/ all grids].
Statistical Analysis The work of analyzing was performed with SPSS 10.0 and EXCEL 2003. With two kinds of material IOL the percentage of PCO at year 1 and 2 and the PCO of the serious grade were compared with each other. The differences between the two IOLs were analyzed by using a t test.
RESULTS
The Percentage of PCO The analytical area of the posterior capsule Sensar AR40e IOL we studied with the POCO software was 14.4±1.51mm2,silicone IOL 14.73±0.89mm2. Statistically there was no significance between the two cases (P=0.66). Thus we could come to the conclusion that there was no difference between the sizes of the analytical areas in the two kinds of IOL we intended to study. In Sensar AR40e IOL group, the percentage of PCO in the analytical area was 0.32±0.13(100%) one year after the surgery, while silicone IOL group was 0.39±0.17(100%), statistically there was no significance between the two cases either (P=0.37). Two years after the surgery at follow up, we found the percentage of PCO was as follows. Sensar AR40e IOL was 0.42±0.20 (100%), silicone IOL 0.34±0.18(100%), (P=0.50). As far as the percentage of PCO at year 1 and year 2 was concerned, there was no significance statistically either by comparison between the two cases mentioned above (Table 1).
Serious Grades of PCO In Sensar AR40e IOL group, the serious grade of PCO was 0.50±0.30 in one year, while silicone IOL group was 0.63±0.35. Statistically there was no significance between the two cases (P=0.52). Two years after the surgery at follow up, the serious grades of PCO were as follows: Sensar AR40eIOL was 0.82±0.58 while silicone IOL was 0.55±0.35 (P=0.69, Table 2).
Table 1The percentage of PCO with Sensar AR40e IOL and silicone IOL in 1 and 2 years postoperatively
Table 2Serious grades of PCO with Sensar AR40e IOL and those of PCO with silicone IOL in one or two years after the surgery
DISCUSSION
Having conducted the study of the implantation of PMMA, silicone capsule and acrylic IOL after the surgery Hayashi et al [13] found that the rate of PCO occurrence in the acrylic group was lower than that of silicone group, and whats more the frequency of the silicone group was lower than that of PMMA group. The results of our research were different from theirs, the cause of which might have some relationship with the different evaluation criterion of PCO. It is easy to give rise to some observation bias. Therefore it needs us to objectively evaluate PCO in the form of quantification.
The main problem in the study of the various kinds of frequency of PCO is the use of different methods in the definition of PCO[4]. Most of them are the relatively subjective methods, so to speak. All of the methods were affected by a large quantify of confusing factors. Now the main methods of evaluation to be adopted are as follows: 1) vision. What we are most concerned with is that the patients can see objects as normal people can do. But the majority of the patients we had observed were those who had got on in years. Their sensitivity in visual sense must have some relationship with their age as well as with their reaction to objects and so on, but in many cases of the study the patients were usually taken for a group of people with the same sensitivity and reaction. Thats why there came the experiments bias, which should be taken into consideration in the design of studies and selecting the number of samples. 2) Grade division of clinical ophthalmologists’ observation. Although there is a criterion of grade division for cataract such as LOCSⅢ[5], yet there has been no standard for PCO widely accepted so far. Grade division of clinical ophthalmologists’ observation is short of accuracy and repetition. 3) Grade division of surgical result .This touches upon the point whether the patient needs another surgery, such as different rate of incision of YAG capsulotomy, which doesn’t belong to an objective standard either because of the different evaluation criterions of the laser doctors. 4) Grade division of the quantification system of image analysis. Many researchers invented advanced systems to capture and analyze images, from which we found that there were more frequencies of differentiation and bias in the course of taking images than those of image analysis. Thus the work of taking a group of images for the same sample is much more meaningful than that of repeating the work of analyzing the same image in the respect of repetition [6]. Apart from this the images stored in the computer can be used for analysis again later on. Whats more, they can also be used to analyze central 3mm, special areas, etc. Only through the evaluation of the posterior capsule in the form of quantification and the visual evaluation in detail as a supplement, can the standard we ll obtain be considered as a sole objective standard.
We employed the system of imagetaking and analysis of posterior capsule based on the PCO software, in the process of which we found some following advantages compared with the previous subjective evaluation. 1) Effectivity and reliability. when the experienced ophthalmologists evaluated the PCO images of the patients, they found that the observation result was fully in conformity with the result analyzed by the system. 2) Possibility of repetition. Taking images of the patients we took a few images at a time. From these images we carefully selected two we were satisfied with in focus, contrast and clarity and then compared them with each other. Although sometimes the first one and the second one were not analyzed at the same time, the results of the analysis through the software were all the same. Nevertheless, there were still some patients who came back to have a second examination one week after the first time they had their images taken, so that they had their PCO images taken once again. In spite of some changes of location of head, size of pupils and focus, the result of images was conformable with the previous one on the whole. What it shows is that the system has an advantage of high repetition. The very reason is that the photographic analysis of the computer is free from the affection of various factors coming from the outside, such as the examiners psychological factor, thinking inclination etc. Only there are these advantages, is there such a high conformity of the analytical result. 3) Possibility of reappearance between the evaluators. The same system was operated by different doctors and the same patient examined by several different doctors, but the different doctors had the same result of the same image. This is very important. The images obtained by the system were designed and analyzed by the same observer in the experiment, but part of them had been evaluated by some other experienced doctors. Since they were processed by the same computer, there came a very approximate result. In our opinion the best way is that we should set up a centre of interpreting images like that of fundus fluorescence angiography. In the centre the images are analyzed by special experienced and welltrained professionals so that there will be a guarantee of a result to the greatest degree of conformity. 4) Early discovery of PCO. The rate of YAG capsulotomy adopted in the large quantity of studies is not only thought of as a method of being subjective, but only when the matter of opacification affected the patients vision, will it be meaningful. It usually takes a few years of follow up to reach the state of curing diseases. In many cases the large part of the surface of the posterior capsule was covered with a thin layer of lens epithelial cells but it didnt affect the vision. While the observer discovered PCO with a slit lamp, LECs had developed to a certain extent. The image analysis in the form of quantification obtained with a computer has a high degree of analysis, correct quantity of exposure, correct focus and enough illumination. Furthermore the photographic images can be examined and exchanged at any time. All the merits of the digitized method can never be obtained by any other methods.
Although the system commits less error in the operation and has high repetition and reappearance in the evaluation of PCO, there are still some problems in its performance. 1) Sometimes the ratio of contrast between the photographic images was lower, and furthermore there were some complex graphs with borders dim. At that time the quality of some images can be improved by the advanced image processing system. Anyhow the best way is to employ a camera with higher resolution and a wide displaying screen to make the feature of a fine part come out more clearly. What we adopted was a 15″ CRT monitor. Nevertheless we suggest the use of a 21″ or more LCD monitor so that the analysis for images becomes more accurate and the eyes of the observer can be protected simultaneously. This is because it takes a long time for the observer to concentrate his attention on the fixed displaying screen during the operation. By doing like that it will do great harm to the observer’s eyes. 2) The depth of field of the system is too shallow yet. Any opacification in the depth of field may appear on the retroillumination photographs. Although the opacification of the anterior vitreous found during the operation didnt bring forth some artifact and affect the quality of photographs, yet it is very important to remove the opacification of photographs of the patients vitreous and cornea. If condition permits, we should try our best to employ the advanced camera. 3) The Purkinje light reflexes always appear in the centre of the image. As we adopted the coaxial illumination with high brightness, there is no way to process the filtering of the software. What we can do is to have light reflexes covered, among which some data will lose. Thus the software needs upgrading afterwards. 4) How to define the analytical area. POCO defined the analytical area as the optical area where the posterior capsule hasn’t been covered by the anterior capsule. If the capsulorhexis of the anterior capsule is away from the front part of IOL surface, the edge of IOL is taken for the border of the analytical area. This is because PCO began at the peripheral posterior capsule at the earliest stage. The advantage of defining this way is to discover PCO at its early stage. There are other doctors who defined it as the centre of the visual axle where the edge of IOL and the pupillary border play the role of a border. Both of the two methods defining the analytical area have some defects, for it is likely that there are some changes of the capsulorhexis after surgery. IOL may slant or deviate from the direction of the centre and the size of pupils may not stabilize forever. Judging from the defects we have to make some corresponding selections according to the different studies.
The authors have no proprietary interest in any of the materials or equipment discussed in this study.
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