Effects of Morning and Evening Narrowband Blue Light and Myopic Defocus on Axial Length in Humans

To investigate the effects of morning and evening narrowband blue light exposure on axial length, and to examine the short-term effect of morning blue light combined with myopic defocus on axial length.

For objective 1, 18 individuals underwent 60 minutes of narrowband blue light exposure (460 nm) in the morning (9:00-11:00 AM) and evening (5:00-7:00 PM) of the same day. The axial length values were normalized to the average of the morning and evening axial length values. For objective 2, 27 young adults were exposed to 60 minutes of narrowband blue light while wearing a + 3.00 D lens over the right eye. Broadband white light was the control condition in both experiments. Axial length was measured using Lenstar LS900.

In the first objective, a significant reduction in axial length was observed after exposure to morning blue light compared to evening blue light (-10.0 ± 3.96 µm vs.-0.67 ± 3.30 µm; p = 0.02), whereas no such effect was observed with broadband white light exposure (0.0 ± 3.53 µm vs. -2.50 ± 4.23 µm, p = 0.70). While the broadband white light exposure did not alter the normal diurnal variation in axial length (+2.35 ± 1.82 µm vs.-6.25 ± 2.21 µm, p = 0.04), blue light diminished such a pattern (-4.12 ± 1.72 µm vs. -2.00 ± 2.00 µm, p = 0.48). In the second objective, the myopic defocus did not influence axial length under either narrowband blue or broadband white light conditions.

The short-term narrowband blue light exposure led to a significant decrease in axial length in the morning than evening exposure, with a likely influence on the daily variation of the morning-evening difference in axial length. Morning blue light exposure with lens-induced myopic defocus did not provide additional short-term modulation of axial length.