Near work, light levels and dioptric profile - Which factor dominates and influences the short-term changes in axial length?

Purpose: Given the agonistic nature of near work to promote axial elongation and the antagonistic nature of time outdoors to prevent myopia, we aimed to investigate the following: (a) how the short-term effect of near work performed outdoors (Experiment 1) influences axial length and (b) how near work performed in two different dioptric profiles (uncluttered and cluttered) alters the changes in central axial length (Experiment 2). Methods: Forty-six adults (age range: 19-32 years) participated in the study. In Experiment 1, 22 participants completed a 15-min distance task and a reading task in both the outdoor (similar to 30,000 lux) and indoor (similar to 70 lux) locations. In Experiment 2, 24 participants performed the same reading task at a study desk in uncluttered and cluttered reading environments. Pre- and post-task ocular biometry measurements were performed for each session using a non-contact biometer. Results: In Experiment 1, a significant increase in axial length from baseline was found after performing reading tasks in both outdoor (mean +/- SEM: +12.3 +/- 3.4 mu m, p = 0.001) and indoor locations (+11.9 +/- 3.1 mu m, p = 0.001). In Experiment 2, axial length increased significantly from baseline to post reading task, in both uncluttered (+17.9 +/- 3.5 mu m, p < 0.001) and cluttered reading environments (+19.2 +/- 2.9 mu m, p < 0.001). No significant changes in axial length were observed either between outdoor and indoor locations (p = 0.92) or between the uncluttered and cluttered reading environment (p = 0.75). Conclusion: Independent of light intensity (outdoor or indoor location) and dioptric profile of the near-work environment (uncluttered or cluttered), a 15-min reading task led to a significant increase in axial length. While the long-term effects of these findings need to be evaluated, practitioners should emphasise how near work can reduce the beneficial effects of time outdoors, while providing recommendations related to time outdoors for myopia control.