Parental myopia influences the likelihood of a child being myopic. However, the increase in its prevalence worldwide suggests that environmental factors and lifestyle are determinants. If nothing is done, the current myopia epidemic is expected to affect 50% of the world’s population by 2050, becoming the main cause of irreversible blindness due to retinal detachment, glaucoma or cataracts.
What is myopia?
During growth, the normal eye adapts and adjusts to maintain sharp vision through a process called emmetropization. During emmetropization, the length of the eye and the curvature of the cornea and lens must adjust to properly focus light on the retina (the part of the eye that collects light and sends “images” to the brain).
Myopia occurs when the eye does not fit properly, resulting in an eye that is too long (axial myopia) or a cornea and lens that are too curved (refractive myopia). This causes light to focus in front of the retina, resulting in blurred or out-of-focus vision.
Outdoor weather protection paper
A study conducted in Australia between 2003 and 2005, involving more than 4,000 children, allowed for the first time to associate greater time spent outdoors with a lower prevalence of myopia. Other intervention studies, in which the time spent by children outdoors was increased, demonstrated a reduction in the onset of myopia and, although spending time in open spaces does not seem to slow it down once it has started, it does slow its progression.
In contrast, increased time spent indoors, such as during the Covid-19 pandemic, was associated with increased incidence of myopia.
But why? It’s because of physical activity. No. This beneficial effect on vision has nothing to do with carrying out activities, but simply with being outdoors. Everything suggests that the protective effect of time outdoors has to do with the unique characteristics of sunlight (intensity, spectral distribution, etc.) that artificial lighting lacks. But it also has to do with the increase in spatial frequency (greater amount of detail) associated with environments with vegetation and the greater viewing distances outdoors compared to indoor activities (reading, writing, using digital devices).
What effect does light have on eye development?
Regarding light, two characteristics must be taken into account: the intensity and the type of light or wavelengths.
The intensity is obviously higher outside, with the sun as the only light source. Even on a cloudy day, the light intensity is at least 10 times higher than that of indoor lighting.
If the prevalence of myopia in large Asian cities is so high compared to cities in Europe or Australia with comparable educational levels, this is most likely due to the negative impact of large buildings on light levels.
Bob Marley already said it in his song Concrete Jungle: “Darkness has covered my light” (“Darkness has covered my light”). It is true that in modern buildings with large windows the intensity might be similar to that outside. However, in that case the glass filters the light spectrum making it not comparable to outside light either. Windows reduce a large part of UVA and near-infrared light.
Epidemiological studies and animal experiments have shown that daily exposure to high illuminance, and specifically UVA light and short wavelength blue light (460 nm), specifically reduce the axial elongation of the eye that causes myopia. And dopamine, the brain neurotransmitter that increases with age, has a lot to do with this effect of light on ocular development. likes Instagram or a pat on the shoulder from our boss and it makes us feel so good.
Light stimulates the release of dopamine by specific cells in the retina, the amacrine cells. There, dopamine modulates the refractive growth of the eye (compensatory or emmetropization) by inhibiting axial growth, thickening the choroid (inner layer of the eye behind the retina) and improving blood flow to the eye.
Other cells involved in refractive development are a type of photoreceptors (light sensors) of the retina, the ipRGC ganglion cells, involved in the biological circadian clock and in the release of melatonin that controls sleep-wake cycles.
And reading or screens don’t affect myopia?
Yes, the amount of time children spend doing “close work” has been linked to a higher risk of myopia and eye enlargement. Who hasn’t been told “don’t get too close to the TV or you’ll end up wearing glasses…”? I don’t think our parents had scientific evidence of this fact, but there are multiple epidemiological studies that support it.
Given this situation, there are two possible options to curb myopia. One is to develop a pharmacological treatment with dopamine or analogues. The other is to create the right conditions for children to spend at least 2 hours outdoors.
The first requires much more research to ensure that there are no side effects related to the multiple functions of dopamine on the body, behaviour or emotions. The second involves adapting the lighting in schools and leisure facilities, and increasing the time children spend outdoors, preferably in open areas with vegetation.
Noelia Valle, Professor of Physiology, Francisco de Vitoria University
This article was originally published on The Conversation. Read the original.
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