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<div><p>Background</p><p>Myopia has been a rising problem globally. Early-onset myopia significantly increases the risk of high myopia later in life. Despite the proven benefits of increased outdoor time, optimal strategies for preventing early-onset myopia in premyopic children need further investigation.</p><p>Methods</p><p>This randomized controlled trial aims to evaluate the efficacy of optical (Defocus Incorporated Multiple Segments [DIMS] spectacle lenses) and pharmacological (0.01% atropine eye drops) interventions in preventing myopia among premyopic preschoolers. We will recruit 234 premyopic, asymptomatic 5-to-6-year-old children who will have received cycloplegic autorefraction examination in a countywide kindergarten eye care program in Yilan County, Taiwan. Eligible participants will be randomly assigned to DIMS spectacles (n = 78), 0.01% atropine (n = 78), or usual care (n = 78). In the DIMS group, preschoolers will be instructed to wear spectacles at home before entering elementary school but to wear them all the time after school entry. In the atropine group, subjects will be given 0.01% atropine eyedrops nightly throughout the study period. All participants will be encouraged to spend time outdoors for 2 hours every day. During the 18-month study period, cycloplegic spherical equivalent (SE) refraction, axial length, and subfoveal choroidal thickness will be measured every three months, and parents-administered questionnaires regarding risk factors for myopia will be performed every nine months.</p><p>Primary outcome</p><p>The change in mean cycloplegic SE.</p><p>Secondary outcomes</p><p>The cumulative percentage of incident myopia, the cumulative percentage of a fast myopic shift of SE, and the changes in mean axial length.</p><p>Other pre-specified outcomes</p><p>The time to myopia onset, alteration in subfoveal choroidal thickness, and levels of near work/outdoor activities.</p><p>Trial registration</p><p>This study is registered at <a href="http://www.clinicaltrials.gov/" target="_blank">www.clinicaltrials.gov</a> as <a href="https://clinicaltrials.gov/ct2/show/NCT06200194" target="_blank">NCT06200194</a>.</p><p>Conclusion</p><p>This trial will provide insights into myopia prevention strategies and inform new eye care policies for early identification and intervention in premyopic preschoolers.</p></div>