Jeffery, G. et al. (2021). Scientific Reports. (Morning deep red light improves aged human vision)

Tntroduction: Myopia is recognized as a pro- gressive eye disease. The aim of this study was to evaluate the frequency and associated factors of clinically significant axial length (AL) shorten- ing among myopic children following repeated low-level red light (RLRL) therapy.

Methods: The clinical data that were collected for the myopic children aged 3–17 years who received an RLRL therapy delivered by home- use desktop light device that emitted light at Version:0.9 StartHTML:0000000105 EndHTML:0000004033 StartFragment:0000000141 EndFragment:0000003993650 nm for at least 1 year, were reviewed. The clinical data included AL, spherical equivalentrefraction (SER), and visual acuity measured at baseline and follow-up. The primary outcomes were frequency of AL shortening of [ 0.05 mm, [0.10 mm, and [ 0.20 mm per year, and associated factors of AL shortening per year.

Results: A total of 434 myopic children with at least 12 months of follow-up data were inclu ded. The mean age of participants was 9.7 (2.6) years with SER of -3.74 (2.60) diopters. There were 115 (26.50%), 76 (17.51%), and 20 (4.61%) children with AL shortening based on cutoffs of 0.05 mm/year, 0.10 mm/year, and 0.20 mm/ year, respectively. In the multivariable model, AL shortening was signifificantly associated with older baseline age, female gender, and longer baseline AL or greater spherical equivalent refraction (all P \0.05). Among AL shortened eyes, the mean AL difference (standard deviation, SD) was -0.142 (0.094) mm/year. Greater AL shortening was observed among children who were younger and had longer baseline AL
(all P \0.05).

Conclusions: More than a quarter of children had AL shortening [0.05 mm following RLRL therapy, and the overall mean AL change was -0.142 mm/year. Further studies should explore the mechanisms underlying AL shortening.

INTRODUCTION

Myopia is characterized by progressive axial elongation and loss of distance vision. It is estimated that it will affect half of the world’s population by 2050, 40% of whom are projected to be high myopia [1, 2]. Axial length (AL) elongation is associated with structural and functional alterations in the eye, which increa ses the risk of vision-threatening conditions such as macular hemorrhage, retinal detach ment, cataracts, and glaucoma [3]. Therefore, AL control is an underlying principle for myo pia treatment and preventing vision loss [4, 5].

In infant rhesus monkeys, it has been observed that ocular shape is able to recover, to some extent, from experimentally induced myopia once the myopic stimulus is removed [6–10]. After removing the form deprivation and hyperopic defocus stimulus, elongation of the vitreous chamber would slow down, result ing in AL comparable with that of the con tralateral eye [7]. This is consolidated by a meta analysis, suggesting eye shortening also takes place in non-human primates following myopic defocus, mainly through modulations in vitre ous chamber depth [11]. The eyes of tree shrews had a greater proportion of AL recovery com pared with other species in response to myopic defocus [11–18]. This reduces the severity of myopia by increasing spherical equivalent of myopia, and therefore reduces the chances of vision-threatening complications.

In humans, the presence of AL shortening following myopia therapies has only rarely been observed [19, 20]. Repeated low-level red light (RLRL) therapy has  merged as an innovative and promising approach for the control of myopia progression [21]. We recently reported the efficacy and safety of RLRL for controlling AL in Chinese children with myopia in a mul ticenter randomized control trial (RCT), where exposure to RLRL twice daily markedly reduced myopia progression and AL elongation over 1 year [22]. Unexpectedly, a certain proportion of children exhibited AL shortening following RLRL therapy, which is a novel and important finding. Given that the RCT was conducted under strict inclusion and exclusion criteria, the effect of RLRL on AL shortening in real clinical settings with significant population hetero geneity remains unknown. Therefore, a retro spective analysis of RLRL users from 11 hospitals located in six provinces in China were analyzed, with the aim of investigating the fre quency and associated factors of AL shortening, as well as its associated factors in clinical settings.