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Logo of bmjThis ArticleThe BMJ
BMJ. 2007 October 27; 335(7625): 842.
PMCID: PMC2043436

Occlusion studies are ambiguous

Philip Lempert, ophthalmologist

The editorial1 and report2 about occlusion treatment for amblyopia include ambiguities. Loudon and Simonz did not consider anatomic defects as the aetiology for severe visual impairments, attributing poor outcomes solely to compliance failure.1

Amblyopia is a diagnosis of exclusion applied after eliminating organic causes of impaired vision. Optic nerve hypoplasia, for example, is an important cause of childhood visual disability3 and perhaps the most common optic disc anomaly seen in clinical practice.4 Accurate diagnosis of this condition requires imaging and measurements that were apparently not used in this study.2

A study of the literature found no studies of natural history of amblyopia, no firm evidence on its impact on quality of life, no randomised controlled trials of treatment versus no treatment, and only one prospective controlled trial of screening.5 The report by Stewart et al2 failed to include controls. The mean age of the subjects in the study was 5.6. Improved responses to eye charts would be expected as a result of children learning to read, regardless of treatment protocols. Their findings that “the final level of attainment for all ages between 3 and 8 years is the same” and the similarity of responses to different amounts of occlusion reinforce the likelihood that patching has little to do with final results.2 The lack of an untreated cohort makes the attribution of improvement solely to occlusion treatment doubtful.

The gold standard for clinical trials includes placebo groups. Until amblyopia treatment studies include untreated subjects for comparison and incorporate objective diagnostic methods they will continue to produce uncertain results.


Competing interests: None declared.


1. Loudon SE, Simonz HJ. Occlusion therapy for amblyopia. BMJ 2007;335:678-9. (6 October.) [PMC free article] [PubMed]
2. Stewart CE, Stephens DA, Fielder AR, Moseley MJ. Objectively monitored patching regimens for treatment of amblyopia: randomised trial. BMJ 2007;335;707-14. (6 October.)
3. Oster SF, Sretavan DW. Connecting the eye to the brain: the molecular basis of ganglion cell axon guidance. Br J Ophthalmol 2003;87:639-45. [PMC free article] [PubMed]
4. Brodsky MC, Baker RS, Hamed LM. Pediatric neuro-ophthalmology. New York: Springer-Verlag, 1996.
5. Snowdon S, Stewart-Brown SL. Preschool vision screening: results of a systematic review. Report 9. York: NHS Centre for Reviews, 1997

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