¡¡¡¡We employed the system of imageª²taking 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 examiner¬ðs 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 wellª²trained 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¬ð 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 didn¬ðt 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¡å CRT monitor. Nevertheless we suggest the use of a 21¡å 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 retroª²illumination photographs. Although the opacification of the anterior vitreous found during the operation didn¬ðt bring forth some artifact and affect the quality of photographs, yet it is very important to remove the opacification of photographs of the patient¬ðs 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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¡¡¡¡4 Findl O, Buehl W, Menapace R.Comparison of 4 methods for quantifying posterior capsule opacification. J Cataract Refract Surg 2003;29(1):106ª²111

¡¡¡¡5 Chylack LT Jr, Wolfe JK, Singer DM, Leske MC, Bullimore MA, Bailey IL, Friend J, McCarthy D, Wu SY. The Lens Opacities Classification System III. The Longitudinal Study of Cataract Study Group. Arch Ophthalmol 1993;111(6):831ª²836

¡¡¡¡6 Wang MC, Woung LC. Digital retroilluminated photography to analyze posterior capsule opacification in eyes with intraocular lenses. J Cataract Refract Surg 2002;26(1):56ª²61

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