Risk factors for posterior capsule opacification.

I mprovements in techniques, instrumentation, and intraocular lens design appear to have been associated with declining rates of posterior capsule opacification following cataract surgery. While morbidity associated with posterior capsule opacification and its treatment, Nd:YAG laser capsulotomy, is limited, progressive opacification affects quality of vision and visual function, while capsulotomy requires additional patient visits, consumes additional surgical resources, and introduces the potential risks of cystoid macular oedema and retinal detachment. Therefore, a better understanding of the mechanisms of posterior capsule opacification and its retardation would have obvious immediate benefits. Moreover, control of capsular optical and biomechanical characteristics following cataract extraction is essential if dynamic accommodative intraocular lenses, which change in optical conjugation power in response to ciliary body motion translated via the zonules and capsular bag, are to provide consistent and sustained performance. In addition to providing further evidence suggesting an increased risk for posterior capsule opacity associated with specific features of intraocular lens design independent of material, the study presented by Mian and co-authors in this issue of the BJO (p 1453) supports the observation that we as yet do not have a complete understanding of all of the features that govern the behaviour of the capsular bag following cataract surgery; in this case, inability to exercise control over this process resulted in laser capsulotomy in up to 7.5% of cases at 24 months. Moreover, the comprehensive review provided by the authors draws attention to inconsistency in the literature with regard to its assessment of risk factors and strategies for the development of posterior capsule opacification after cataract surgery. This, in turn, obfuscates research directions for strategies to control the process of capsule opacification. Well informed and sceptical readers will point out, as the authors acknowledge, that some previous studies, which have specifically addressed the issue of the relative risk for posterior capsule opacification associated with one piece acrylic compared with three piece acrylic intraocular lenses, have failed to demonstrate a significant difference in risk for posterior capsule opacity. As a previous study by Wallin and colleagues supports the authors’ observations of an increased risk associated with the one piece design, one must consider explanations for these discrepancies, in so far as they may represent inconsistencies in study design or reporting. One must first ask if a negative study that fails to identify a difference in outcomes is based upon the evaluation of relatively insensitive or unreliable parameters. This is a particular problem in the evaluation of posterior capsule opacification. Laser capsulotomy represents but a proxy for the process of opacification; it might be argued that it is a perfectly reasonable measure to study if our goal is to reduce the additional burden that the procedure places on patients and the medical system but, in the event that opacification which fails to meet criteria for treatment induces some compromise of visual function, there remains benefit to the reduction of these sub-interventional threshold levels of capsule opacity. Moreover, the goal of capsule control for reliable long term accommodative intraocular lens function requires an understanding of the mechanisms of posterior capsule fibrosis at an earlier stage than that associated with the need for laser intervention.