Author Affiliation: Duke Eye Center, Durham, North Carolina.
In the article by Dr Zhao and colleagues1 on acupuncture for amblyopia, it is unclear how long subjects actually wore optimal spectacles prior to randomization to patching or acupuncture. This issue is important because studies have shown that spectacles alone are a powerful treatment for amblyopia.2- 4 The authors wrote that, “At a screening visit, protocol-specified spectacles were prescribed. . . The baseline examination was scheduled within 2 weeks of the screening visit. New spectacles were provided for all participants on the day of the baseline examination. . . With the participants wearing the new spectacles, VA (visual acuity) was measured in each eye. . . The better of the 2 VA scores was used as the baseline VA to assess eligibility. . . After eligibility was confirmed, participants were randomly assigned. . . Treatments were started within 2 days after randomization.” So it seems that subjects were given new spectacles and randomized within 2 days of receiving them. If so, this is inconsistent with the authors' statement that “Patients were eligible if they had worn optimal spectacles for at least 16 weeks prior to enrollment,” and “The spectacles should have been worn until VA was stabilized.” The spectacles should have been or were actually worn for at least 16 weeks? If many subjects were randomized before visual acuity stopped improving with spectacles, I am not surprised that both patching and acupuncture groups had robust improvement. In an equivalence study (unlike a superiority study), factors such as new spectacles or a recent change in spectacles that predispose to improvement in both groups will bias toward supporting the study hypothesis (in this case, equivalence between patching and acupuncture).
Wallace DK. Acupuncture for Amblyopia: Study Design Considerations. Arch Ophthalmol. 2011;129(9):1242–1243. doi:10.1001/archophthalmol.2011.239