Effect of Increasing Time Spent Outdoors on Myopia Prevention in School-Aged Children in Northeast China

Uncorrected visual acuity (UCVA) was measured for the right eye, then the left eye, with a E Standard Logarithm Vision Acuity Chart (GB11533-2011) in 5-grade notation (5- LogMAR), with illumination of the chart around 500lx. If one of the eyes UCVA was less than 5.0, then tests with combined lenses were conducted among the poor eye-sighted for confirming the types of ametropia (normal, myopia, hyperopia or other eye diseases)．All the measurements were recorded.

The parents and children underwent an interview together. The questionnaire included questions on children's gender, ethnicity, region of habitation; questions on parental education level, the monthly family income and whether the parents were myopic or not;. The interview also included questions on the amount of time spent for learning (reading or writing), screen time (television, computer, etc) and time spent outdoors after school in recent 7 days.

A random subsample (12.8%) underwent cycloplegia. After ensuring that there was no risk for a medical mydriasis, cycloplegia was performed at baseline and intervention after 1 year in the Shenyang Aier Ophthalmology Hospital, respectively. Ocular biometric parameters (axial length, corneal curvature, anterior chamber depth and IOP) were measured in both eyes of all participants. Axial length, corneal curvature and anterior chamber depth were measured with IOL Master (intraoeular len master, IOL. Master) (Carl Zeiss Meditex, Jena, Germany); Intraocular pressure (IOP) measurement was obtained using a non-contact tonometry (NT-510, NIDEK, Gamagori, Japan). Cycloplegia was achieved by 0.5% tropicamide eye drops. Six drops of tropicamide 0.5% were administered at 5-minute intervals for both eyes. Refractometry was performed 20 minutes after the last cycle of cycloplegic eye drops by retinoscopy (YZ-24, Suzhou, China).