Conventional occlusion versus pharmacologic penalization for amblyopia

Methodological quality of the review: High confidence

Author: Li T, Shotton K.

Region: Ireland, United States of America (USA) and Spain

Sector: Amblyopia

Sub-sector: Conventional occlusion, atropine penalisation

Equity focus: None specified

Review type: Effectiveness review

Quantitative synthesis method: Narrative analysis

Qualitative synthesis methods: Not applicable


Amblyopia (referred to as lazy eye) is a common childhood condition, and is defined as defective visual acuity in one or both eyes, which is present with no demonstrable abnormality of the visual pathway and is not immediately resolved by wearing glasses. Treatment for amblyopia usually starts with prescribing necessary glasses to correct visually important refractive errors followed by promoting the use of the amblyopic eye.

Research objectives

To assess the effectiveness and safety of conventional occlusion versus atropine penalization for amblyopia.

Main findings

The authors included three randomized or quasi-randomized controlled trials with a total of 525 amblyopic eyes. Out of these, the largest enrolled 419 participants while the lowest constituted 36 participants. The participants were both boys and girls aged from two to 10 years with all types and levels of amblyopia. Studies included data from Ireland, USA and Spain.

Evidence from three trials (one of good methodological quality) suggested both conventional occlusion and atropine penalization produced visual acuity improvement in the short-term (six months) and long-term (24 months) in the amblyopic eye after initiation of therapy. The results of this review show atropine penalization to be as effective as conventional occlusion, although the amount of improvement achieved differed among the three trials. Although both treatments were well tolerated, compliance was better with atropine penalization. Atropine penalization can be used as first line treatment for amblyopia.

This review identified several gaps in research, including long-term stability of treated amblyopia and the risk of reoccurrence of amblyopia, comparison between methods of occlusion to determine whether they are comparable, such as partial occlusion and total occlusion, improved methods of documenting compliance of treatment and cost-effectiveness analyses comparing atropine penalisation and conventional occlusion.


The authors inclusion criteria consisted of randomized controlled trials (RCTs) and quasi-randomized controlled trials (CCT) that enrolled participants of any age with unilateral strabismic, ansiometropic, or mixed amblyopia. Authors originally planned to include trials that compared conventional occlusion with any pharmacologic therapy, including systematic therapy such as levodopa and carbidopa. Primary outcome measures included best-corrected visual acuity of the amblyopic eye and change in visual acuity after 12 months of treatment. The secondary outcome was the change in binocular function measured by change in stereo acuity according to the stereopsis test applied in each trial.

The authors conducted a search on Central, Medline, Embase, LILACS, the WHO International Clinical Trials Platform, preference lists science citation index and ongoing trials. Two authors independently screened abstracts and full text articles, abstract data and assessed the risk of bias.

The authors conducted a systematic synthesis of the evidence from the randomized and quasi-randomized controlled trials for the effectiveness and safety of conventional occlusion therapy compared to pharmacological penalization in treating amblyopia. Due to heterogeneity and methodological limitations of included studies, pool effect estimates in a meta-analysis was difficult.

Applicability/external validity

The authors did not discuss the generalizability of the results.

Geographic focus

The authors included studies from Ireland, USA and Spain. They did not discuss the applicability of the findings to low- and middle-income countries.

Quality assessment

Overall, there is high confidence in the conclusions about the effects of this study. This review is based on relatively comprehensive searches of the literature and authors used appropriate methods to reduce risk of bias in terms of study selection, data extraction and analysis. However, minor limitations were identified: the authors did not contact experts and did not search journals and conference proceedings by hand to identify additional studies as part of the search strategy. The authors acknowledged limitations of this review, for instance reviewers noted that there was insufficient information to assess the risk of selective reporting bias in two of the included studies, and did not draw strong policy conclusions.

Li T, Shotton K. Conventional occlusion versus pharmacologic penalization for amblyopia. Cochrane Database of Systematic Reviews 2009, Issue 4. Source