Does convergence, not accommodation, cause axial-length elongation at near? A biometric study in teens

To determine whether convergence rather than accommodation has a primary ef fect on the changes in axial length and other biometric components during n ear fixation, we measured the anterior chamber depth, lens thickness, vitre ous length and axial length in the right eyes of 124 young male subjects wh ile their left eyes focused at distance (6 m) and near (20 cm). The measure ments were performed before and after cycloplegia in the right eye, so we a imed to study biometric components of the eye in the states of ac-commodati on and nonaccommodation, but converging at near. While the left eye focused at near, the axial length increased significantly with and without cyclopl egia (p < 0.0005 and p < 0.0005). The vitreous length was the main increasi ng ocular biometric component at near both with and without cycloplegia (p < 0.044 and p = 0.001, respectively). At near, there was no difference betw een two mean axial length and two vitreous length measurements both with an d without cycloplegia (p = 0.672 and p = 0.595, respectively), Under cyclop legia, anterior chamber depth also increased significantly at near fixation (p = 0.012). Axial elongation at near fixation, mainly due to an increase in vitreous length, may result from the effect of accommodative convergence rather than accommodation itself. Much use of convergence, not accommodati on, may be one of the contributing factors in adult onset and adult progres sion of myopia.