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In high school, I started having trouble reading things written on the black board. I was diagnosed with short-sightedness, or myopia, a condition in which one could see nearby objects but had trouble bringing objects farther away into focus. At our school itself, the number of students wearing eye-glasses to correct this condition always only increased.
Before the COVID-19 pandemic, there had been signs of myopia acquiring pandemic proportions. In China and parts of East Asia in particular, as many as 60% of school-going students are myopic. In India, 7.5% of school students are affected. Some experts have predicted that at the current rate, 50% of the world’s population will be short-sighted by 2050.
Myopia increases the risk of cataract, glaucoma and retinal detachment, which could potentially lead to blindness.
However, a study published in June 2021 suggests that simple lifestyle changes could prevent short-sightedness. The scientists’ work – based on studying mice – suggests that exposure to the violet component of sunlight, which is lacking in indoor conditions, could be key to preventing myopia.
The eye is an optical device that focuses light for the brain to process, forming images that we see, just like a smartphone’s camera. The eye uses a lens to focus light onto brain cells present in the inner layer of the eyeball, or the retina. The shape of the eyeball helps with focusing.
In people with myopia, the eyeball is elongated, as a result of which the eye can’t properly focus the light onto the retinal brain cells.
Scientists suspect both lifestyle and genetic factors are responsible. Myopia is prevalent among individuals who spend more time indoors and who perform activities that involve objects being closer to the eye, like reading. This said, how one’s lifestyle affects the shape of one’s eyeballs is not fully understood.
Studies have also suggested that parents with myopia are likelier to have children with myopia than parents who aren’t myopic. This means genetic factors could be at work as well.
An older study, in mice, found that the retina responds to sunlight and encourages the section of dopamine, a neurotransmitter that helps defend against myopia progression.
But to the surprise of the scientists behind the study, indoor lighting conditions didn’t seem to play a protective role, however. They traced this difference to the fact that the violet component of sunlight (wavelength 360-400 nm) is missing in indoor LED lights. The UV-protection coating on some windows also prevent light of this wavelength from passing through.
In the new work, another group of researchers made juvenile mice wear goggles with powered lenses that blurred their vision. As eye development in juvenile mice depends strongly on their environment, the powered lens led to the mice developing elongated eyeballs, inducing artificial myopia.
These mice were grown in differently lit environments that allowed the scientists to study the effects of lighting on eyeball elongation.
They found that in mice exposed to violet light, myopia progressed more slowly. They also found that violet light exposure only during the evening helped to slow myopia, indicating the importance of violet light exposure in tandem with the body’s circadian rhythm.
They also performed similar experiments with mice whose genes had been edited to prevent the expression of a protein called neuropsin.
Present in the retinal cells, neuropsin was thought to mediate the relationship between violet light and dopamine secretion.
The researchers found that neuropsin expression and violet light are crucial to maintain the thickness of the choroid layer of eye wall – a layer consisting of blood vessels to the eye. As myopia progressed, this layer became thinner, which then caused the eyeball to become distended.
Exposure to violet light prevented the choroid layer from thinning.
Recall that the findings are in mice. If the results are confirmed in humans as well, they could mean simple lifestyle changes can help keep myopia at bay. Companies that manufacture anti-UV sunglasses and contact lenses may also have to redesign their products, and help keep eyes healthy.
The researchers’ elucidation of a specific mechanism by which the eyeball becomes elongated – involving the choroid layer and neuropsin – could also mean pharmaceutical companies can develop drugs to help with myopia.
Finally, considering the amount of money people spend every year on corrective glasses and surgeries, governments need to invest more in studying myopia’s causes and preventive strategies.
The importance of receiving sunlight in the evening, while studied in mice, shouldn’t be lost on parents during the COVID-19 pandemic. They have been spending more time indoors thanks to the lockdowns, and their children have been spending more time in front of screens, for their online classes. They should both be mindful of the adverse effects of this lifestyle, and spend some time outside when and where they can.