Accommodation-induced biometric changes in ciliary muscle, trabecular meshwork, and Schlemm’s canal: comparison of eyes in high myopia

PURPOSE: To evaluate accommodation-induced changes in the ciliary muscle (CM), Schlemm's canal (SC), and trabecular meshwork (TM) in eyes with and without high myopia, and to assess the associations among these structures during accommodation. METHODS: 116 eyes from 57 healthy control (HC) and 59 high myopia (HM) were assessed across two experiments. In the first experiment, pilocarpine-induced accommodation was applied to 78 eyes, while in the second, a -5 diopter (D) accommodative stimulus was used on 38 eyes. Anterior segment images were captured via swept-source optical coherence tomography before and after each accommodation stimulus. Measurements included the maximum thickness of CM and the anterior length of CM, the length of TM, and the area of SC. Statistical analyses evaluated group differences and correlations. RESULTS: Drug-induced and - 5D stimulation increased the maximum thickness of CM and the area of SC's levels while decreasing the anterior length of CM's levels. In the HC group, the length of TM was larger in the accommodative state, mediating the relationship between changes in the maximum thickness of CM and the area of SC. Conversely, these changes and correlations in the length of TM were insignificant in HM eyes. The length of TM increased with axial length and elongation in the anterior length of CM across all subjects; however, accommodation-related changes diminished as axial length (AL) and the anterior length of CM increased. Causal mediation analysis demonstrated that the anterior length of CM mediated the relationship between AL and the length of TM elongation. CONCLUSIONS: In two trials, accommodation-induced changes in the CM, TM, and SC were observed in eyes with or without HM, with reduced TM and SC response in HM. Differences in CM, TM, and SC behavior during accommodation between the HC and HM groups suggest that CM contraction may reshape the aqueous humor outflow channels.