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Editor,—I congratulate the authors of this study for making the conceptual leap that control trials of intervention for amblyopia are necessary.1 To my knowledge, this is the first study of its kind and while it has some limitations for which it will no doubt be criticised, it shows the way for future researchers in this field.
What the authors have shown is that occlusion for 1 hour a day had no long term additional benefits over spectacle correction alone. I am interested to know why they chose this occlusion regime. It would also have been helpful if the initial and final acuities attained for each patient had been documented. Are they also convinced that all their patients were truly amblyopic, and not just children with refractive errors who became more cooperative with repeated testing?
Editor,—We would like to thank Mr Clarke for his support of our belief that occlusion therapy should be subject to controlled trials.
As stated in our paper, we chose to adopt a minimal occlusion regimen as this has previously been found to be beneficial while minimising the burden placed on parents and children. We would stress, however, that our study was not primarily an attempt to evaluate this occlusion regimen, rather to address some methodological issues which future studies will need to take into account. We could, therefore, have legitimately adopted any regimen of our choosing.
Clarke’s concern that our subjects may not have been amblyopic but merely possessing refractive errors raises important questions for both taxonomy and treatment. Children presenting with significant refractive errors and a loss of visual acuity (in the absence of other pathological findings) will fall into one of three categories: those whose visual acuity loss is completely (and instantaneously) ameliorated by refractive correction; those whose acuity loss is restored over a period of weeks or months; and a third category, those in whom acuity, as in the preceding category improves over time, but never reaches 6/6. Conventionally, children in the first category would not be diagnosed as being amblyopic while those in the third category meet the standard diagnostic criteria of amblyopia. But what of those in the second category? Most authorities would also apply the label of amblyopia to these patients although we cannot differentiate the factors which may contribute to the improvement associated with “long term” spectacle wear (for example, a putative anti-amblyopic effect, perceptual learning, familiarisation with test and tester) or define the nature of the underlying pathophysiology. In our study, none of the subjects who completed the trial attained 6/6 (category 3 above) though as alluded to in our paper and confirmed by subsequent experience, had the spectacle (“pretreatment”) phase of the trial been extended, some subjects may have attained normal acuity (category 2 above). We acknowledged in our paper that increased cooperation with repeated testing could have contributed to the improvement seen in all of our subjects.
With the exception of one particular subject of interest, we did not, in addition to stating the changes in the mean and standard deviation of subjects’ recorded visual acuity at each phase of the trial, present data from individuals. We would be happy to make this available to anyone wishing to undertake further analysis.
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