Binocular dynamics of accommodation, convergence, and pupil size in myopes

The purpose of this work is to study the dynamics of the accommodative response as a function of the subject's refractive error, as a first step in determining whether an anomalous accommodative function could affect emmetropization or trigger myopia progression. A secondary goal was to establish potential relationships between the speed of accommodation and other parameters in the accommodation process. Parameters related to the speed and amplitude of accommodation, convergence, miosis, and change in high-order aberrations were measured during the accommodative process for 2.8 D demand in 18 young healthy subjects (mean age 25.0 ± 4.7 years) with a range of refractive errors between 0 and -7.5 D (spherical equivalent). Measurements were performed in real time (25 Hz) with an open-view binocular Hartmann-Shack (HS) sensor using a GPU-based processing unit. Correlation coefficients were calculated between refractive error and each computed variable. Additionally, the speed of accommodation was correlated with all the other parameters in the study. Correlation coefficients with refractive error had non-zero values for several parameters of the accommodative response but p-values were higher than 0.05 except in two cases: with pupil miosis speed (R = -0.49, p = 0.041) and with lag of accommodation (R = -0.57, p = 0.014). Additionally, correlation values with p-value < 0.05 were found between accommodation speed and convergence duration (R = 0.57, p = 0.014), convergence speed (R = 0.48, p = 0.044), and pupil miosis amplitude (R = 0.47, p = 0.049). We did not find strong evidence of a link between myopia and altered dynamics of the accommodation process. Only miosis speed was found to be correlated to refractive error with p < 0.05, being slower for myopes. On the other hand, increased lag of accommodation tends to be associated to larger refractive errors. Additionally, our data suggests that the faster the accommodation, the faster and longer the convergence and the larger the pupil miosis.