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 effect on the changes in axial length and other biometric components during near fixation, we measured the anterior chamber depth, lens thickness, vitreous length and axial length in the right eyes of 124 young male subjects while their left eyes focused at distance (6 m) and near (20 cm). The measurements were performed before and after cycloplegia in the right eye, so we aimed to study biometric components of the eye in the states of accommodation and nonaccommodation, but converging at near. While the left eye focused at near, the axial length increased significantly with and without cycloplegia (p < 0.0005 and p < 0.0005). The vitreous length was the main increasing ocular biometric component at near both with and without cycloplegia (p < 0.044 and p = 0.001, respectively). At near, there was no difference between two mean axial length and two vitreous length measurements both with and without cycloplegia (p = 0.672 and p = 0.595, respectively). Under cycloplegia, 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 accommodation, may be one of the contributing factors in adult onset and adult progression of myopia.
D000065:Accommodation, Ocular / Q000502:physiology*; D000293:Adolescent; D000328:Adult; D000867:Anterior Chamber / Q000000981:diagnostic imaging; D001699:Biometry; D003290:Convergence, Ocular / Q000502:physiology*; D005123:Eye / Q000000981:diagnostic imaging* / Q000187:drug effects; D005403:Fixation, Ocular / Q000502:physiology*; D006801:Humans; D007908:Lens, Crystalline / Q000000981:diagnostic imaging; D008297:Male; D009184:Mydriatics / Q000494:pharmacology; D009799:Ocular Physiological Phenomena; D014331:Tropicamide / Q000494:pharmacology; D014463:Ultrasonography