Dynamic Changes in Schlemm Canal and Iridocorneal Angle Morphology During Accommodation in Children With Healthy Eyes: A Cross-Sectional Cohort Study

Abstract

Purpose: The purpose of this study was to explore changes in Schlemm canal (SC), trabecular meshwork (TM), and iridocorneal angle (ICA) morphology during accommodative effort in children and young adults. Methods: We acquired anterior segment optical coherence tomography images (AS-OCT) of the ICA and ciliary muscle (CM) of both eyes of 50 children age 4 to 16 years with healthy eyes, at two levels of accommodation: 2.5 and 15 diopters (D). Semiautomated nasal ICA measurements were as follows: angle opening distance at 500/750 μm (AOD-500, -750), trabecular iris space area at 500/750 μm (TISA-500, -750), and trabecular iris angle at 500/750 μm (TIA-500, -750). Manual measurements were as follows: anteroposterior and radial SC diameter (SC-APD, SC-RD), cross-sectional area of SC (SC-CSA) and TM height (TMH), TM length (TML), and TM density (TMD). CM width was measured at 1, 2, and 3 mm from the scleral spur (CM-1, CM-2, CM-3). For each parameter, a three-level random-effects model was fitted to estimate differences between the two levels of accommodation. Results: With accommodative effort, SC diameters and CSA increase significantly, as do TM length and iridocorneal angle parameters. With increasing age, SC dimensions reduce. Angle parameters are smaller in eyes with greater spherical equivalent (hypermetropia). Conclusions: AS-OCT can be used to visualize dynamic morphologic changes in outflow structures with physiologic accommodation. The increase in SC dimensions with accommodative effort may contribute to the regulation of IOP in children.