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C.E. Stewart, M.J. Moseley, D.A. Stephens, A.R. Fielder, ROTAS Cooperative; Modelling of Treatment Dose–Response in Amblyopia . Invest. Ophthalmol. Vis. Sci. 2005;46(13):3595.
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Purpose: To determine the minimum dose–rate that maximized the beneficial effects of treatment in the Randomized Occlusion Treatment for Amblyopia Study (ROTAS). Methods: Data were obtained from 82 participants (mean age = 5.5 ± 1.5 years) with amblyopia associated with strabismus (n=19), anisometropia (n=34), and both anisometropia and strabismus (n=28). Seventy–nine subjects required refractive correction and underwent 18–weeks spectacle wear ('refractive adaptation') before entering the occlusion phase. Seven children gained good and equal visual acuity with refractive adaptation alone. Those subjects with persistent amblyopia were randomized to either 6 hours or 12 hours occlusion per day. Outcome variables (logMAR visual acuity) were assessed at six–weekly intervals during refractive adaptation and at weekly intervals during occlusion until gains ceased to be statistically verifiable. Patch wear was objectively recorded using an occlusion dose monitor. Outcomes were defined as follows: logMAR change, residual amblyopia (log units) and the proportion of the deficit corrected (%). Results: Seventy–five children entered the occlusion phase and were randomized to prescribed occlusion doses of 6 hours per day (n=36), and 12 hours per day (n=39). Dose–rates (hrs/day) actually worn did not significantly differ between groups (p=0.06) (6–hour group: 4.2 ± 1.7, 12–hour group: 6.2 ± 3.9). Children were grouped according to dose–rates actually worn, 0–3 (n=19), >3–6 (n=32) and >6–12 (n=24). Significant differences (p=0.04) in observed changes in visual acuity were shown between the 0–3 group and >3–6 and, >6–12 groups (change in visual acuity logMAR; 0–3 group: 0.18 ± 0.17, >3–6 group: 0.26 ± 0.19, >6–12 group: 0.30 ± 0.16). Significant differences in residual amblyopia (p=0.004) and proportional improvement (p=<0.0001) were also found between the 0–3 group and >3–6 and, >6–12 groups (residual amblyopia, 0–3 group: 0.31 ± 0.15, >3–6 group: 0.11 ± 0.11, >6–12 group: 0.16 ± 0.16; proportional improvement; 0–3 group: 33 ± 39%, >3–6 group: 77 ± 30%, >6–12 group: 67 ± 33%). Conclusions: Monitoring actual doses received using occlusion dose monitors indicates that children wearing over 3 hours per day show significantly more improvement than those wearing less than 3 hours per day. Modelling of the dose–response function has revealed that all dose–rates exceeding 4 hours per day provide essentially similar gains. In order to achieve such dosing actual dose prescribed should approximate to 6 hours per day.
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