Why the world is becoming more shortsighted

By 2050, one in every two people will be shortsighted and one in every 10 people will have high (severe) myopia, which means they are highly likely to go blind.

Scientists say that people spending more time in full-time education is to blame and steps must be taken to prevent myopia from progressing to high myopia.

In a study published in the British Medical Journal in June, researchers presented “strong evidence” that more time spent in education was a risk factor for myopia (short-sightedness or near-sightedness), the leading cause of visual impairment in the world.

Researchers suggest that factors relating to the nature of modern education such as more time studying and working with computers and less time spent outside may explain the correlation between short-sightedness and education levels.

The evidence is particularly apparent in South East Asian countries, where up to 90 per cent of school leavers are myopic. In these countries, there is an emphasis on intense education (which involves close up work during reading or studying) from an early age, and there is little time for play outdoors. This has led to almost half of children becoming shortsighted by the end of primary school.

RISK FACTOR

British researchers from the University of Bristol and Cardiff University sought to find out whether education was a risk factor for myopia, or whether shortsighted children were more likely to spend more years seeking education.

They analysed data from more than 67,000 men and women aged 40 to 69 years, and found that every additional year spent seeking education was associated with more myopia.

Take two people with similar levels of intelligence. One attends school to university level, while the other leaves school after high school. The one who attended school for longer (the university graduate) is more likely to become shortsighted. Moreover, the university graduate would have myopia that requires glasses for driving.

The researchers found there was little evidence to suggest that myopia led people to remain in education for longer.

“Exposure to more years in education contributes to the rising prevalence of myopia, and highlights the need for further research and discussion on how educational practices might be improved to achieve better outcomes without adversely affecting vision,” the researchers concluded.

CLOSE-UP WORK

In another study on the link between education and myopia published in the journal Nature Genetics in June, researchers analysed 4,000 participants aged 40 to 79 years. They measured cognitive functioning (mentally planning ahead and problem solving) and examined the refractive power of the eyes of the participants, to determine how much their eyes had to adjust to produce a sharp image.

Those with myopia scored higher in the cognitive functioning test than those without, and the scores rose with the severity of short-sightedness.

It is easy to see why people who spend more time in education-related activities are more likely to develop myopia. People who read a great deal, perform a lot of close-up work, also called near work, usually in poor levels of daylight.

In these conditions, the eye adjusts by having the internal layer send a message to the external layer to increase the length of the eyeball. If the eyeball becomes too long, the distance between the lens and the retina increases.

The eye changes shape to compensate for moving the retina closer to the focal point and the cornea and the lens focus the image just in front of the retina, instead of on it, making distant objects blurry. In short, the person has become shortsighted, only able to see close objects clearly.

DEGENERATIVE DISEASE

One may wonder why myopia is a big deal, yet it can simply be corrected by wearing glasses. But it’s not that simple.

Early onset of myopia may mean progress to high and potentially pathological myopia. Pathological myopia is a degenerative form of the disease that can cause atrophy of the retina (that lines the back of the eye).

People with high myopia and pathological myopia are at higher risk of myopic choroidal neovascularisation, a condition characterised by the growth of new, unstable blood vessels beneath the retina.

If untreated, it can cause vision loss that may then become permanent. Severe short-sightedness is also associated with an increased risk of retinal detachment, macular degeneration (blurred or no vision at centre of visual field), premature cataracts and glaucoma.

Preventing myopia reduces the need for vision correction, and prevents these potentially blinding eye conditions later in life.

When caught early, myopia can be treated, but not fully cured. As more people become shortsighted, there will be need for comprehensive eye care services to control the progression from myopia to high myopia.

With the number of people with vision loss from high myopia expected to increase seven-fold by 2050, according to a 2016 study published in the journal Ophthalmology, researchers are studying how to prevent myopia from becoming the leading cause of permanent blindness worldwide in three decades.

One of the aspects under study is the effect of time spent outdoors during childhood, as a protective mechanism against the development of short-sightedness.

Studies have shown that children who spend more time outside are less likely to need glasses for near-sightedness, with data suggesting that a child who is genetically predisposed to myopia is three times less likely to need glasses if he or she spends more than 14 hours a week outdoors.

Researchers recommend that children spend at least two hours every day to prevent myopia from developing or progressing.

"While screens are contributing to children spending more time indoors than in previous years, research shows they are not the direct cause of the increased incidence of myopia.

Optometrists need to make their patients aware that less than 60 minutes' exposure to light outdoors per day is a risk factor for myopia. Even for those with myopia already, increasing time spent outside is likely to reduce progression,” said optometrist Scott Read in a 2016 study.

A study published last year in the journal Current Biology, sought to explain the role of outdoor light in preventing myopia.

Researchers said that a dysfunction of a cell in the retina causes myopia, and that the dysfunction may be linked to the amount of time a child spends indoors and away from natural light.

The retinal cell – which is highly sensitive to light – contains a signal to focus images in the eye and controls how the eye grows and develops during childhood.

It responds slowly to light becoming brighter, and is sensitive to whether an image is in focus. If the cell instructs the eye to grow too long, images are not focused on the retina, causing near-sightedness that requires corrective glasses.

The indoor light spectrum has high red/green contrast, which activates clusters of photoreceptors in the human eye, creating the equivalent of an artificial contrast image on the retina. It is likely that the retinal ganglion cell would be overstimulated by such patterns, causing over-growth of the eye, leading to myopia.

The researchers said that finding the gene specific to this cell and turning its activity up or down could help induce or cure myopia.

Apart from encouraging children to spend more time outdoors to prevent the risk of developing myopia from environmental factors, researchers also recommend yearly eye check-ups.

“We need to ensure our children receive a regular eye examination from an optometrist or ophthalmologist, preferably each year, so that preventative strategies can be employed if they are at risk. These strategies may include increased time outdoors and reduced time spent on near based activities including electronic devices that require constant focusing up close,” said study co-author Prof Kovin Naidoo.

Regular eye checks are particularly helpful because myopia tends to develop during childhood and adolescence, and interventions can be applied if it is caught early.

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Break from the screens to protect your eyes

Using computers, phones and other electronic screens is not just considered near work, just like extended reading, writing and other intensive close-up activities that can raise the risk of developing myopia, it can also cause digital eyestrain with symptoms such as dry eye, eye strain, headaches and blurry vision.

The symptoms may be temporary or frequent and persistent. To protect your eyes:

1. Take a 20-second break from near work every 20 minutes and look at an object that is 20 feet away

2. Look up and out of the window every two chapters of a book

3. Alternate reading e-books with real books to avoid digital eye strain

4. After completing a level in a video game, look outside the widow for 20 seconds

5. Sit at arm’s length (25 inches) from the computer screen and position the screen so that your eye gaze is slightly downward

6. Avoid using a computer outside or in brightly-lit areas as the glare on the screen can cause eye strain

7. Adjust the brightness and contrast of the computer screen to reduce eye strain. If the screen is brighter than surrounding light, your eyes work harder to see

8. Use a matt screen filter to reduce glare from the screen

9. Use good posture when using a computer or reading

10. Remember to blink when watching a screen

11. Use artificial tears to refresh eyes when they feel dry

12. Ensure children spend at least one to two hours outdoors every day

Source: American Academy of Ophthalmology

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How we see and what happens when things go wrong

In a normal eye, light rays enter the eye through the cornea, pupil and lens. The cornea is the clear, round dome covering the iris, the coloured ring in the centre of the eye, and the pupil, the black circle in the middle of the iris.

Light rays pass through the vitreous, a clear, gel-like substance that fills the middle of the eye, and are focused on the retina, the light-sensitive tissue lining the back of the eye. As light enters the eye, the cornea and lens focus it to give clear vision. Seventy per cent of the eye’s focusing power comes from the cornea, and 30 per cent comes from the lens.

The macula, a very small area at the centre of the retina, gives people fine, pinpoint central vision. For eyes to see, light rays must be bent (refracted) by the tear film, the cornea and the lens to focus on the retina. The area of retina surrounding the macula gives us peripheral (side) vision. The retina converts light rays into impulses that are sent through the optic nerve to your brain, where they are recognised as images.

In the normal, healthy eye, the cornea is clear, smooth and round and the lens is clear, allowing light rays to pass through unobstructed and be focused sharply on the retina.

If the cornea is not as smooth, clear or round as it should be, or the eyeball is too long or too short, light rays bend (refract) at odd angles, leading to blurry or distorted vision.

This inability to achieve sharp focus is called refractive error, and is the most common eye problem. Refractive errors include nearsightedness (myopia); farsightedness (hyperopia) and astigmatism.

The eye will also have focusing problems if the naturally clear lens is cloudy due to cataract; if it isn’t as flexible as it should be (causing presbyopia), or has other problems with the way it functions.

Myopia occurs when the eye is longer than normal or has a cornea that is too steep. As a result, light rays focus in front of the retina instead of on it. The eye does not bend light properly to a single focus to see images clearly. This allows you to see close objects clearly, but distant objects appear blurred. Signs of myopia include eyestrain, headache, squinting to see properly and difficulty seeing distant objects such as road signs or a blackboard.

Myopia is diagnosed by an eye doctor (ophthalmologist) by using a standard vision test, which involves reading letters on a chart 20 feet away. The doctor can also tell what is causing the myopia by shining a special light into your eyes and seeing how light reflects off your retina.

The ophthalmologist can also measure the amount of refractive error you have to determine the right prescription to correct it.

If the myopia is mild, it is called low myopia. Severe myopia is known as high myopia. Vision is corrected easily with glasses or contact lenses, which work by refocusing light rays on the retina to compensate for the shape of the eye.

Glasses can also protect your eyes from harmful ultraviolet light rays using a special lens coating that screens UV light rays. When refractive or LASIK surgery is used to correct vision, it works by reshaping the cornea to adjust the focusing ability of the eye.

Patients with high myopia have a higher risk of developing a detached retina, glaucoma and cataracts. If the retina detaches and is discovered early enough, a surgical procedure can repair it. Regular eye examinations by an ophthalmologist can monitor changes in the retina that might lead to retinal detachment.

There is no scientific evidence to suggest that eye exercises, vitamins or pills can prevent or cure myopia.

Source: American Academy of Ophthalmology