Does Convergence, Not Accommodation, Cause Axial-Length Elongation at Near?

Abstract

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.

Which one is more causative for myopia progression: Accommodation or convergence?

“…Our previous study supports this hypothesis suggesting that much use of convergence, rather than accommodation, may be a contributing factor in progression of myopia [2]. In that study, we observed a significant axial length elongation during near fixation both with and without cycloplegia, that is, with and without accommodation [2].…”

“…Our previous study supports this hypothesis suggesting that much use of convergence, rather than accommodation, may be a contributing factor in progression of myopia [2]. In that study, we observed a significant axial length elongation during near fixation both with and without cycloplegia, that is, with and without accommodation [2]. In our studies, we found that axial elongation during near focusing support the hypothesis that convergence may be a more important causative factor inducing myopia rather than accommodation [2][3][4].…”

Overcorrecting minus lens therapy in patients with intermittent exotropia: Should it be the first therapeutic choice?

“…It is known that accommodation and/or convergence caused by reading and/or near-work cause myopia or myopic progression [21][22][23][24]. It has been concerned that accommodative effort required with minus lenses may induce myopia or enhance myopic progression [14].…”

Myopic anisometropia: ocular characteristics and aetiological considerations

“…Forces exerted by the extraocular muscles during convergence are thought to have the potential to lead to changes in axial length . Bayramlar, Cekic and Hepson concluded that transient axial elongation associated with near work is a result of convergence rather than accommodation after observing significant vitreous chamber elongation measured with ultrasonic biometry in young subjects following near fixation with and without cycloplegia. However, Read and colleagues reported that axial length measured with partial coherence interferometry appears largely unchanged in adults both during and following a period of sustained convergence.…”