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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（略）
Table 2Serious grades of PCO with Sensar AR40e IOL and those of PCO with silicone IOL in one or two years after the surgery（略）
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.
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