This study aimed to investigate the effect of reading and near work on myopic development in emmetropic boys in school age. It involved totally 114 children in two groups. Right eyes of 67 randomly selected students (mean age = 12.93) with mean 6 h of reading and near work (Group 1) were compared with the right eyes of 47 apprentices (mean age = 12.96) working as skilled laborers (Group 2). Cycloplegic refraction, keratometric readings and biometric measurements including anterior chamber depth (ACD), lens thickness (LT), vitreous chamber depth (VCD) and axial length (AL) were performed for 3 years at 18 month intervals. Two analyses were conducted: (1) for subjects in both groups with baseline refractive error from + 0.50 to - 0.50 D: (2) for all subjects in both groups with baseline refractive error from + 1.00 to - 1.00 D. For subjects with baseline refractive error of + 0.50 D, myopic shift was present in 20 of 41 (48.8%) in group I and in seven of 37 (18.9%) in group 2 at the end of the study. The magnitude of the myopic shift was 0.56 and 0.07 D in group I and I respectively. For subjects with a baseline refractive error of +/- 1.00 D. myopic progression was present in 40 of 67 (59.7%) in group I and in 10 of 47 (21.3%) in group 2 at the last readings. In this larger refractive range, the magnitude of the myopic shift was 0.61 and 0.12 D in group I and 2. respectively. The mean ACID, VCD and AL were significantly higher in the last readings after 36 months than in the first readings (for each, P = 0.0001) in group 1. There was no statistically significant difference between two measurements of these parameters in group 2. The final keratometric dioptric readings were lower than the first values (for each, P = 0.0001) in both groups at the end of the study. This prospective and controlled study suggested that reading and near work., important environmental factors, might cause refractive myopic shifts in emmetropic students. The myopic shift was primarily related to significant increases in ACID, VCD and AL in this young age group. (C) 2001 Elsevier Science Ltd. All rights reserved.