Greater axial elongation associated with low accommodative lag: new insights on accommodative lag theory for myopia.

Abstract

We aimed to test the accommodative lag and mechanical tension theories for myopia by assessing the influence of the lag of accommodation on axial elongation by using three different near targets that are known to influence the accommodative response differently. Forty-two young adults were recruited for the study. Axial length was measured using a non-contact biometer, before and immediately after a 15minute visual task, with one of the three near targets placed 20cm from the eye: reading text from a paper, reading text from a smartphone and watching a video on a smartphone. The accommodative response was determined using an open-field autorefractor while the participants viewed the near target monocularly. Lag of accommodation was significantly different for the three tasks: watching a video (mean±standard error of the mean [SEM] 0.92±0.10 D); reading text on the smartphone (0.59±0.08 D); and reading text on paper (0.24±0.09 D). There was a significant (p<0.05) increase in axial length after reading text from a paper (10.5±1.9µm after 15-min) and reading text from a smartphone (5.2±2.7µm), but not after watching a video on a smartphone (-0.5±1.7µm, p=0.47). Vitreous chamber depth increased significantly more with the reading tasks compared with watching a video (reading text from a paper and smartphone: 33.9±4µm and 31.7±4µm vs. watching a video on a smartphone: 14.6±5µm, p=0.001). Greater changes in axial length associated with the low lag of accommodation failed to support the theory that lag of accommodation during visual tasks could be the trigger for axial elongation. Reading on paper and smartphone at the closest reading distance may stimulate high accommodative demand and axial elongation as a consequence, possibly due to increased "ciliary muscle tension" during accommodation.