Effect of intraocular lens design on posterior capsule opacification

Methodological quality of the review: High confidence

Author: Buehl W, Findl O.

Region: Austria, Turkey, Japan, Sweden, United States of America (USA), Finland, Lithuania, Denmark and United Kingdom (UK)

Sector: Cataract

Sub-sector: Clinical outcomes

Type of cataract: Age-related cataract

Equity focus: None specified

Review type: Other review

Quantitative synthesis method: Meta-analysis

Qualitative synthesis methods: Not applicable

Background

Extracapsular cataract extraction (ECCE) with posterior chamber intraocular lens (IOL) implantation is the preferred surgical technique for the treatment of cataract in many countries. However, leaving the posterior capsule intact during surgery may result in long-term complications, primarily posterior capsule opacification (PCO).People with PCO experience decreased visual acuity, impaired contrast sensitivity, and glare disability. Interventions for preventing PCO include modifications in IOL geometry design. The introduction of sharp optic edges appears to reduce the incidence of PCO and this review summarizes the available evidence on this topic.

Research objectives

To summarize the effects of intraocular lens (IOL) geometry, including modifications of the IOL optic (especially optic edge design) and haptics, on the development of PCO.

Main findings

26 prospective randomized and controlled trials were included in the review, in which different IOL designs were compared with each other or to ‘standard’ IOLs. These were conducted in different countries including Austria, Turkey, Japan, Sweden, USA, Finland, Lithuania, Denmark and the UK.  In five out of seven studies, visual acuity was better in sharp-edged IOLs than in round-edged IOL. The PCO score was significantly lower with sharp-edged IOLs but did not differ significantly between one-piece and three-piece open-loop IOLs. Authors noted that ‘Because of the significant difference in the PCO score, sharp-edged IOL optics should be preferred to round-edged IOL optics.’ They also mentioned that it is important to use a standardized method to quantify PCO. A common PCO scoring method would make the comparison of trials easier.

Methodology

Authors included randomized controlled trials with a follow-up of at least 12 months which compared different IOL designs with each other or to ‘standard’ IOLs. Participants of included studies were people with age-related cataract without prior sight-threatening ocular disease (glaucoma, corneal disease, uveitis, traumatic or complicated cataract [for example, zonular weakness], retinal disease, history of diabetes mellitus with diabetic retinopathy) who had cataract surgery with implantation of an IOL in the capsular bag.

Trials were identified from the Cochrane Central Register of Controlled Trials, (CENTRAL) (which contains the Cochrane Eyes and Vision Group Trials Register) on the Cochrane Library, MEDLINE, EMBASE, and Latin American and Caribbean Literature on Health Sciences (LILACS). Reference lists of all identified trials and previous reviews were searched for additional trials. Manual searches of journals were not done specifically for this review. There were no language or date restrictions in the electronic searches for trials. The searches were last updated in January 2007. To rate the level of evidence, authors used a standardized form provided by the Cochrane group.

Data from studies collecting comparable outcome measures with similar follow-up times were summarized. Studies with missing standard deviation (SD) values were not excluded, but could not be incorporated in the meta-analyses. Dichotomous outcomes were presented as odds ratios or risk ratios. Continuous outcomes were presented as the mean difference.

Applicability/external validity

Authors did not discuss the applicability/external validity of results.

Geographic focus

The review took into account all income settings. Two middle-income countries were included: Turkey and Lithuania. The review mentioned the particularly negative impact of PCO in low-income countries due to limitations with Nd:YAG laser treatment. This makes the review highly relevant when considering IOL choice in low-income settings.

Quality assessment

Authors conducted a thorough literature search in order to ensure all available studies were included in the review, avoiding publication and language bias. Although authors did not provide a table or summary of the assessment of each included study, they used appropriate criteria to assess the quality and risk of bias in analysing them. Limitations of the included studies for meta-analysis were acknowledged.  Overall, high confidence in conclusion regarding the effects was attributed to this study.