Axial length and choroidal thickness changes accompanying prolonged accommodation in myopes and emmetropes

The time course of elongation and recovery of axial length associated with a 30min accommodative task was studied using optical low coherence reflectometry in a population of young adult myopic (n=37) and emmetropic (n=22) subjects. Ten of the 59 subjects were excluded from analysis either due to inconsistent accommodative response, or incomplete anterior biometry data. Those subjects with valid data (n=49) were found to exhibit a significant axial elongation immediately following the commencement of a 30min, 4 D accommodation task, which was sustained for the duration of the task, and was evident to a lesser extent immediately following task cessation. During the accommodation task, on average, the myopic subjects exhibited 22±34μm, and the emmetropic subjects 6±22μm of axial elongation, however the differences in axial elongation between the myopic and emmetropic subjects were not statistically significant (p=0.136). Immediately following the completion of the task, the myopic subjects still exhibited an axial elongation (mean magnitude 12±28μm), that was significantly greater (p<0.05) than the changes in axial length observed in the emmetropic subjects (mean change -3±16μm). Axial length had returned to baseline levels 10min after completion of the accommodation task. The time for recovery from accommodation-induced axial elongation was greater in myopes, which may reflect differences in the biomechanical properties of the globe associated with refractive error. Changes in subfoveal choroidal thickness were able to be measured in 37 of the 59 subjects, and a small amount of choroidal thinning was observed during the accommodation task that was statistically significant in the myopic subjects (p<0.05). These subfoveal choroidal changes could account for some but not all of the increased axial length during accommodation.