All examinations were conducted in the schools during school hours by optometrists from the Chinese University of Hong Kong. Examinations included best-corrected distant visual acuity testing, cycloplegic autorefraction, and measurements of ocular dimensions with ultrasound. Distant visual acuity of each eye was measured using the Early Treatment Diabetic Retinopathy Survey (EDTRS) chart at 6 m with standard lighting. Cycloplegia was achieved using 1 drop of combined 0.5% phenylephrine and 0.5% tropicamide eye drops (Mydrin P; Santen, Osaka, Japan) instilled three times in the inferior conjunctival cul-de-sac, at intervals of 15 minutes. Automated refraction was performed with an autorefractometer (Topcon KR-7100 autorefractometer; Topcon Corp., Tokyo, Japan) between 30 and 60 minutes after completion of the drug regimen. Three reliable readings were obtained in each eye, and the average of these values was used for analysis. Ultrasound biomicroscopy (Compuscan; Storz Ophthalmic Inc., St. Louis, MO) was performed after cycloplegia. The ocular parameters measured included anterior chamber depth, lens thickness, vitreous chamber depth, and axial length. Three reliable readings were obtained, and the average of these values was used for analysis. All the equipment was maintained in satisfactory working condition, and reliable performance was assured by routine quality control programs.