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The efficacy of occlusion for strabismic amblyopia. Can an optimal duration be identified?
  1. RICHARD HARRAD
  1. Bristol Eye Hospital, Lower Maudlin Street, Bristol BS1 2LX

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    Patching carried out during the sensitive period is thought by clinicians to be an effective treatment for amblyopia.1 2Success rates of patching vary but one study has reported success rates of 90% of patients improving to 6/12 or better within 3 months.3 Parents not uncommonly report difficulty in persuading their children to wear a patch.4 Inpatient treatment by supporting the parents and encouraging the children frequently achieves success.

    A recent systematic review5 was unable to find any randomised controlled trials of treatment of amblyopia and concluded that there was no evidence that treatment worked. They relied heavily on the results of a study which suffered from many flaws in its design.6 7 Nevertheless, if the highest standards are applied, there is no evidence from a randomised controlled trial that patching works as a treatment for amblyopia. It follows that if treatment is ineffective there is no justification to screen for amblyopia and indeed this was the conclusion of the systematic review. Most ophthalmologists do not need to be convinced of the efficacy of patching treatment for amblyopia.

    Cleary (this issue, p 572) has taken advantage of the presence of both compliers and non-compliers in a group of children with amblyopia treated with glasses and patching to carry out a prospective but non-randomised control trial. The numbers are small (only 17 non-compliers) but the two groups are comparable in terms of density of amblyopia and other variables. The logMAR crowded test (Glasgow acuity cards) has been employed and this is ideal for measuring visual acuity in amblyopia; the non-amblyopic eye has been used as a control. The improvement in visual acuity was significantly less in those strabismic children who did not comply with treatment. It is impossible to say that differences between the groups of compliers and non-compliers do not account for the difference in results but, nevertheless, given the paucity of good quality data in this field, these results are of considerable interest. There are several other questions that need to be answered with regard to treatment of amblyopia. Is full time occlusion more effective than part time?8 What is the role of atropine penalisation as opposed to using an eye patch? When should treatment be stopped? What are the reasons for non-compliance with treatment and how can we best measure this? Is there anything more that we can do to help improve compliance? There is considerable research activity under way to address these issues. It is healthy for paediatric ophthalmology to have our assumptions challenged and provides impetus for the construction of a valuable evidence base. At present, a randomised controlled trial of occlusion therapy for anisometropic amblyopia is under way (Wright C, Clarke M, A multicentre randomised controlled trial of treatment of amblyopia detected at pre-school vision screening, personal communication) and the results of this study are awaited with interest.

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