Protective effect of daylight
It is well known that time spent outdoors is linked to lower overall myopia, slowing myopic refraction by around a third [1] [2] [3]. However, for some patients/parents, consistently spending more time outdoors is not always a viable option. A prime (albeit extreme) example of this is the recent COVID-19 pandemic and subsequent lockdowns that prevented millions of children from playing outdoors. Analysis of myopia prevalence before and after the pandemic revealed a devastating side-effect of lockdown on children’s eye health.
Although lockdown is over, its symptoms still linger, such as remote and digital formats for learning and socialising.
Myopia progression is slower in summer compared to winter, although it is unclear whether this is due to differences in intensity, spectral composition, or simply hours of daylight [6]. What complicates things further is that seasonal changes also affect behavioural patterns (e.g. spending time outdoors) and circadian rhythms, and these have a knock-on effect on what light reaches the eye. Thus, the precise aspects of outdoor light exposure that determine its protective properties remain a mystery.
Can artificial light substitute daylight?
The lack of agreement on the mechanisms that underlie myopia onset and progression has led to diverse approaches to myopia management, including optical (Orthokeratology; diffusing/defocusing lenses) and pharmacological (i.e. Atropine) methods. But, armed with our knowledge about the protective effects of daylight, perhaps we can take an entirely different approach: using light. For example, research suggests that simply increasing the brightness of school classrooms may prevent myopia onset in children [7]. However, consensus on what colour light might be most beneficial is lacking.
Blue light therapy
Outdoor light is typically towards the blue end of the spectrum [8]. Blue light stimulates specific cells in the retina, which in turn leads to the release of dopamine, which regulates eye growth [9][10][11]. One experiment exposed adults to different colours of light to investigate the effects on eye growth [12]. After just one hour of exposure to either red or green light, the axial length of the eye had increased and the choroid had become thinner – both of which are associated with myopia. In contrast, exposure to blue light resulted in the opposite effect; shorter axial lengths and thicker choroids.
Another experiment showed choroidal thickening in adults after just 30 minutes daily wear of a blue-green glasses-style headset [13]. Although the changes were very small (a few thousandths of a millimetre) and were only tested over a short period of time, both experiments suggest that blue light may be beneficial for preventing myopia. As a result of such experiments, clinical trials are currently underway to test the longer-term effects of a blue-light therapy approach using a smartphone inserted into a virtual reality headset (MyopiaX, Dopavision: NCT04967287).
Red light therapy
At (quite literally) the other end of the spectrum, research has shown that red light may also reduce myopia, potentially by increasing blood flow to the choroid and reducing inflammation [14].
“Low-level laser therapy” using red light just twice per day for three minutes at a time has been shown to slow myopia progression in children over the course of several months. The devices require the patient to look directly into a device that shines red light into the eyes. Research has shown a reduction in axial length and increased choroidal thickness over the first few months, followed by slowed progression up to a year [15][16] [17] [18] [19]. Clinical trials for one such home-use device are underway (Myproclear, Eyerising: NCT04073238).
While light-therapies hold promise for the management of myopia, it must be noted that the ambiguity surrounding the underlying mechanisms and the lack of long-term follow-up data warrant a cautious approach. The long-term effects of treatment are as yet unknown, and likely require more sensitive measures of retinal structure (such as high-resolution imaging techniques), as simply testing vision may not be sufficient to detect early damage to cells [20].
No therapy has been shown to be effective in every patient, and we do not yet know what happens to the eye after treatment stops. The variability in effectiveness may be due to individual differences in genetics, biology (e.g. retinal topography), behaviour (time spent outdoors, sleeping habits), and diet, just to name a few, and it may be that a personalised approach is needed to maximise treatment efficacy. Further research is needed before we have a full understanding of how light therapy works and how to improve outcomes for patients.
Key points:
Time spent outdoors is protective against myopia in young children.
Brightness, colour, and duration of daylight exposure may all affect myopia.
Thinner choroids, longer axial eye length, and lower dopamine levels are liked to myopia.
Blue-light therapy has been linked to short-term increases in choroidal thickness and reductions in axial length, holding promise as a therapeutic approach to myopia.
Red-light therapy has been associated with an increase in choroidal thickness and a reduction in axial length over a period of months, demonstrating its therapeutic potential.
Long-term follow-up is needed to instil confidence in the safety and efficacy of light-therapy approaches in myopia.
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