Axial elongation associated with biomechanical factors during near work.
Level 3 - non-randomized controlled study
Experimental within-subject controlled physiological study without reported randomization.
PubMed 24413276 · doi:10.1097/OPX.0000000000000166
What was done
Twenty young adults (10 emmetropes and 10 myopes) completed three 10-minute visual tasks preceded by a 10-minute distance primary gaze washout period: near task (2.5 D) in primary gaze, near task (2.5 D) in downward gaze (25 degrees), and far task (0 D) in downward gaze. Axial length, choroidal thickness, retinal thickness, and anterior biometrics were measured at baseline, immediately after, and at 5 and 10 minutes using an optical biometer on a custom-tilted table.
What was found
Axial length increased significantly more during accommodation in downward gaze (mean ± SD change: 23 ± 13 μm at 10 minutes) compared to accommodation in primary gaze (8 ± 15 μm at 10 minutes; p < 0.05). Significant choroidal thinning occurred during accommodation in downward gaze (13 ± 14 μm at 10 minutes; p < 0.05). Downward gaze with accommodation also caused greater changes in anterior chamber depth and lens thickness than accommodation in primary gaze.
Why it matters
This demonstrates that downward gaze posture physically compounds the transient axial elongation and choroidal thinning caused by accommodation during near work.
Limits
The sample was small (20 participants), limiting statistical power to detect subgroup differences between emmetropes and myopes. The study only measured acute biometric changes over a 10-minute duration, leaving it unknown whether these transient shifts contribute to permanent axial elongation or myopia progression.
Cited by
- supports Excessive close-distance viewing during development through the mid-20s alters eyeball shape and contributes to the development of myopia.