الفهرس 
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Abstract
Capsular opacification is a major problem that faces cataract surgeons and affects the resultant visual acuity, it may also impair contrast sensitivity, cause glare or give rise to monocular diplopia.
Visually significant posterior capsular opacification (PCO), remains the most common long-term complication of modern cataract surgery. It occurs in 50% of cases within 2-3 years after surgery. Patients below the age of 40years carry double the risk of developing posterior capsular opacification than those above 40years.
Lens epithelial cells (LECs) left behind in the capsular bag after cataract surgery are mainly responsible for PCO development. Proliferation, migration, epithelial-to-mesenchymal transition(EMT) , collagen deposition, and lens fiber regeneration of LECs are the main causes of opacification . Clinically, there are 2 morphological types of PCO, the fibrosis type and the pearl type. Fibrosis-type of PCO is caused by the proliferation and migration of LECs, which undergo EMT, resulting in fibrous metaplasia and leading to significant visual loss by producing folds and wrinkles in the posterior capsule. Pearl-type PCO is caused by the LECs located at the equatorial lens region causing regeneration of crystallin-expressing lenticular fibers and forming Elschnig pearls and Soemmering ring, responsible for most cases of PCO-related visual .
Posterior capsular opacification is a multifactorial process. The 3 main risk factors for PCO development are patient related (eg, age and ocular disease), surgery related (eg, irrigation/aspiration of the capsule, hydrodissection-enhanced cortical cleanup, sealed capsule irrigation, capsulorrhexis size, and in-the-bag IOL fixation), and IOL related. It is well accepted that PCO incidence is greatly influenced by IOL material and design.
The incidence of PCO varies widely, depending on the cataract surgery technique, IOL material, edge design, history of intraocular inflammation, patient age, the presence of pseudoexfoliation before surgery and diabetes mellitus.
Visual symptoms do not always correlate to the observed amount of PCO. Some patients with significant PCO on slit lamp examination are relatively asymptomatic while others have significant symptoms with mild apparent haze, which is reversed by capsulotomy .
Accurate PCO analysis is important for measuring the effect of treatments that aim to reduce PCO such as intraoperative pharmaceutical treatments or varying types of surgery. It is also an important tool for comparing rates of PCO between the many available lenses, and the rates of progression with these lenses over time. The systems may potentially have other clinical uses such as assessing amount of PCO with regard to potential Nd:YAG capsulotomy surgery.Systems used vary from those using simple slit lamp analysis observation and subjective grading by the observer,to much more complex computerized analysis of digital images obtained with specialized photographic equipment .
The ideal system of evaluation should be objective, easy to perform, have minimal bias and produce a quantifiable PCO value that correlates well with VA changes.
Measures to prevent capsular opacification can be divided into two categories. One strategy is to minimize the number of retained /regenerated lens epithelial cells [LECs] and cortex through cortical cleanup. The second strategy is to prevent the remaining LECs from migrating posteriorly. The edge and the optic of the IOL are criticalin the formation of such a physical barrie .
Research laboratories worldwide attempting to eliminate the problem of PCO development are focusing on several strategies, including improving surgical techniques, IOL materials, IOL designs, use of therapeutic agents, and combination therapy .Recent improvements in surgical techniques and IOL materials and designs have served mainly to delay the onset of PCO rather than eliminate the problem.
Because PCO is predominantly caused by residual LECs in the capsular bag after cataract surgery, several surgical techniques have been attempted for the removal of these LECs at the time of lens extraction.
At present, the only effective treatment of PCO is Nd:YAG laser capsulotomy, which involves clearing the visual axis by creating a central opening in the opacified posterior capsule. Although this procedure is easy and quick, there are complications, including retinal detachment, damage to the IOL, cystoid macular edema, an increase in intraocular pressure, iris hemorrhage, corneal edema, IOL subluxation, and exacerbation of localized endophthalmitis. Changes induced by Nd:YAG capsulotomy have been shown to be affected by IOL material and design