Mechanism Of Preventing And Controlling Myopia By Outdoor Activities

Strictly speaking, the principle of outdoor activities to prevent myopia is still a mystery, just like why dinosaurs died out. This is because outdoor activities have too many influencing factors, but a large number of animal experiments and human controlled observation studies have found that sufficient light may be the most key factor for outdoor activities to prevent myopia. The light here refers to the sunlight that we are most familiar with and indispensable for the growth of all things on earth.

Why can sunlight prevent and control myopia? This starts with the composition of sunlight. The sunlight we are familiar with can be divided into ultraviolet light (UVR wavelength below 400nm), visible light (VIS wavelength 380 ~ 760nm) and infrared light (IR wavelength above 760nm). The wavelength of visible light (i.e. red, orange, yellow, green, blue and violet) is between 380 ~ 760nm, accounting for 52% of all sunlight, infrared light accounts for 43% and ultraviolet light accounts for 5%.

1. Sunshine Vitamin D Theory

A large number of animal experiments have found that the content of vitamin D in animals exposed to long-term sunlight will increase significantly, while compared with those animals with low vitamin D, their ocular axis will be shorter and myopia will be slower. Scientists speculate that sunlight, especially ultraviolet light, can stimulate the body to produce a large amount of active vitamin D, and vitamin D itself is an anti proliferative substance, which may resist the growth and remodeling of sclera and prevent the elongation of ocular axis. In addition, vitamin D itself has the effect of relaxing smooth muscle, so some people speculate that vitamin D can relax the same smooth muscle of the ciliary muscle in the eye and alleviate visual fatigue.

However, some scientists objected that the current research can only prove that individuals with high vitamin D content have a lower probability of myopia, but there is no direct evidence that vitamin D itself can delay the progress of myopia. For example, children who are often exposed to the sun have better bone development, but their skin tends to darken. But this cannot be equated with skin darkening, which can help bones develop better. Therefore, it is not recommended that those who desperately feed their children vitamin D in order to prevent myopia.

2. Sunshine Dopamine Theory

Dopamine is a neurotransmitter chemical. Its most famous function is to transmit the information of excitement and happiness, also known as "happiness hormone". Recently, scientists have found that dopamine may be associated with myopia in addition to being able to "carry happiness". In 2020, a new study in the United States found that mice injected with dopamine daily had significantly slower axial growth and myopia. This is because dopamine, as a neurotransmitter, can inhibit the signal transduction that interferes with the growth of ocular axis. In addition, some scientists have found that dopamine can increase the blood supply of intraocular choroid and thicken the thickness of choroidal layer, so as to delay the growth of ocular axis.

A large number of experimental studies have found that when we are exposed to bright sunlight for a long time, the content of dopamine in our eyes will increase significantly. So we don't have to take dopamine injections every day in order to prevent and control myopia like the poor white mouse. We just need to bask in the sun every day.

3. Spectrum Theory

Previous animal experiments have found that the ocular axis of animals exposed to long wavelengths such as yellow and red light for a long time is longer and myopia is faster than those exposed to short wavelengths such as blue and green light. Scientists speculate that long wavelength light has low refractive index, and light with relatively short wavelength and high refractive index is easier to focus behind the retina, forming hyperopia defocus, which stimulates the growth of the ocular axis.

On sunny days, the visible part of sunlight is mainly blue-green short wavelength. Even on rainy days, the visible light of short wavelength is equivalent to that of long wavelength.

Therefore, scientists speculate that due to the special composition and nature of the visible light spectrum in sunlight, it is easier for visible light to form a myopic defocus in front of the retina after entering the eye, so as to slow down the progress of myopia.