The Effect of Ambient Light Intensity on Transient Changes in Refraction and Ocular Biometric Components following Near Work: A Randomized Clinical Trial.

Purpose: To evaluate the effect of ambient light on transient changes in refraction and ocular biometry after near work. Methods: This single-blind, randomized clinical trial included 87 participants randomly assigned to three groups based on ambient light levels: Group 1 (100-200 lux), Group 2 (300-400 lux), and Group 3 (500-700 lux). Each participant performed 1 h of computer-based text reading at 40 cm. Objective refraction and ocular biometric parameters, including axial length (AL), keratometry, anterior chamber depth (ACD), and lens thickness, were measured before and immediately after the task. Results: The mean ± standard deviation change in spherical equivalent (SE) was -0.72 ± 0.57 diopter in Group 1, -0.39 ± 0.34 diopter in Group 2, and -0.11 ± 0.33 diopter in Group 3 (P < 0.001). AL increased in all groups, with the largest change in Group 1 (45.16 ± 21.60 μm), followed by Group 2 (26.78 ± 13.19 μm) and Group 3 (17.83 ± 9.76 μm) (P < 0.001). Changes in keratometry (P = 0.08), ACD (P = 0.693), and lens thickness (P = 0.999) were not statistically different across the groups. Correlation analysis showed the highest association between SE and AL change in Group 1 (r = -0.703). The multiple generalized estimating equation model revealed a significant association between changes in SE and AL (β = -0.019), lens thickness (β = -0.001), and baseline SE (β = -0.485) in Group 1; AL (β = -0.009) and baseline SE (β = -0.735) in Group 2; and AL (β = -0.016) and baseline SE (β = -0.72) in Group 3. Conclusions: Near visual tasks induce transient myopic shifts and biometric changes, primarily through axial elongation and increased lens power. This effect is influenced by ambient light, with myopic shift intensifying as light levels decrease.