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

Experimental: intervention group

The intervention group undertook interventions by increasing time spent outdoors. The interventions composed of performing two additional recess program lasting 30 minutes outside the classroom that encouraged children to go outside for outdoor activities during recess in both the morning and afternoon during school days within a intervention period of 1 school year.

Conductual: increasing time spent outdoors

The intervention group undertook interventions by increasing time spent outdoors. The interventions composed of performing two additional recess program lasting 30 minutes outside the classroom that encouraged children to go outside for outdoor activities during recess in both the morning and afternoon during school days within a intervention period of 1 school year.

Sin intervención: control group

The control school did not have any interventions.

Changes in uncorrected visual acuity

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.

Questionnaire survey

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.

Changes in ocular biometric parameters

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).