Myopia: What is it?
Myopia simply means “nearsighted”. A child or young adult with myopia is generally able to clearly see things that are near, such as a book or items on grocery shelves.
Things that are farther away, such as road signs, a classroom blackboard, or a friend across the street, appear blurry. In addition to blurry distance vision, symptoms of uncorrected myopia can include:
Left untreated, moderate to severe myopia can lead to serious complications, including blindness. Myopia is commonly first diagnosed when a child is between 8-12 years old, although it can begin in much younger children and progress quickly. With preventive measures, the progression can be slowed, but not reversed. Without preventive measures, myopia will continue to progress until the child’s eye growth is complete, generally around ages 16-21. After that, both distance and near vision are typically stable until around age 40, when normal aging affects the eye’s ability to ‘accommodate’ to close-up vision. Long term complications are more likely in people whose myopia progressed quickly.
How common is myopia?
Globally, at least 28% of people are myopic, and the rate is rapidly rising. The prevalence of myopia varies both by location and by race. In some areas in East Asia 80-90% of people have some degree of myopia. In some areas in Africa the prevalence is around 10%. In the U.S in 2010 the prevalence of myopia in white people was 26% while in Black people it was 14%.
How does myopia develop?
Simply put, normal, clear distance vision requires that rays of light first pass through the cornea — the curved outermost layer of your eye– and then through a curved lens behind your colored iris. Those rays of light, now bent from passing through curves, form an image on the back of the eyeball in an area called the retina. The attached optic nerve relays information about the image to the brain, and the brain responds by providing us with an interpretation of the image.
In a person with myopia, the developing eyeball has elongated. The distance from the cornea and lens in the front of the eye to the retina in the back of the eye is therefore longer than it should be. This is called “axial elongation”. Sometimes the cornea is too curved, causing the light rays to bend at a different angle.
Either way, light that passes through the eyeball can’t reach all the way back to the retina. The image that the optic nerve sends to the brain for interpretation will not be clear.
What causes myopia?
Some causes of myopia can be identified, but not all. We know that:
- Myopia can be genetically passed down from parent to child. Children with at least one myopic parent are more likely to develop myopia. We also know that at least 200 different genes can contribute to myopia. However, scientists are not able to say how significant a role the shared family environment plays.
- Myopia is a characteristic of some genetic diseases. In those cases, the shared environment is not likely be a factor.
- Spending more time outdoors during childhood is protective against myopia. One theory is that exposure to ultraviolet light provides structural stability to a part of the eyeball.
- Children who spend relatively more time indoors on ‘near’ work such as reading have a higher incidence of myopia than children who spend more time outdoors.
- In Europe, the highest rates of severe myopia are found in children with summer birthdays — meaning that they are among the youngest in their grade. These children do ‘near’ work while almost a year younger than their classmates with autumn or winter birthdays.
Myopia can range from mild to severe. Although vision can usually be corrected by one of several methods, the shape of the eyeball or cornea cannot be changed.
How can myopic vision be corrected once it has already developed?
Myopia can be corrected by several methods:
- Contact lenses
- Single-vision lenses can correct distance vision. Unfortunately, improving distance vision alone can make it more difficult to see near-distance objects. Adults over age 40, whose eyes have started to lose their ability to focus on near-distance objects, often wear reading glasses in addition to contact lenses. |
- Multi-focal lenses combine a distance vision component with a near-vision component. Some lenses are similar to bifocal glasses, with the reading component on the bottom of the lens and the distance component on the top. Other lenses have the distance component in the center of the lens surrounded by a donut-shaped reading component.
- Orthokeratology uses custom-fitted hard contact lenses to gently flatten the curve of the cornea, thereby shortening the distance from cornea to retina and allowing light to reach back to the retina.
- Orthokeratology lenses are worn only during sleep and are removed in the morning.
- Around 65% of users achieve 20/20 vision during the day, without glasses.
- It is important to accept that the results are temporary.
- The wearer must pay close attention to cleaning and disinfecting the lenses. As with all lenses, infection is a risk.
- LASIK is the most common surgical procedure for myopia. LASIK is an outpatient procedure in which the surgeon lifts a thin flap from the top layer of the cornea, reshapes the cornea with a laser, and replaces the flap. Unless there are complications, mild discomfort lasts for a few days but the improvement in vision is almost immediate.
- Photorefractive Keratectomy (PRK) is similar to LASIK except that the top layer of the cornea is removed and is not replaced after the cornea is reshaped. The cornea will heal by itself, but discomfort can be expected for longer than with LASIK. PRK is recommended to people with certain corneal conditions.
Scientists and physicians are continually working to develop newer and more effective treatments for myopia. It is worth mentioning that there is no high-quality evidence that vitamins, herbal remedies, or eye exercises are helpful.
If vision can be corrected, why is myopia a problem?
Glasses, contact lenses, and refractive surgery enable the rays of light to project on the appropriate spot on the retina and create a clear image. However, they do not change the shape of the eyeball. Particularly if myopia is severe, damage from axial elongation can cause vision-threatening problems such as:
- A detached retina
- Early-onset cataracts
- Myopic macular degeneration
Can myopia be prevented?
Myopia can’t be reversed, but in children, axial elongation can be minimized. Ophthalmologists recommend:
- Screening children who have risk factors for myopia
- Implementing therapies to prevent progression of myopia
- Providing the vision correction that is most likely to result in healthy visual development
Therapies to prevent progression of myopia include:
- Atropine eye drops:
When used for 2-3 years in children aged 5-18, atropine has been shown to be the most effective way to slow down the progression of myopia.
Nighttime orthokeratology contact lenses work the same way for children as they do for adults. If the child wears the lenses as prescribed, they may permanently decrease myopia progression.
- MiSight Dual Focus contact lenses:
These daily disposable lenses are approved in the US for 8–12-year-olds. They slow myopic progression and axial elongation when worn for 10 hours a day, six days a week.
- More outdoor time and less near-vision time: Given the results of the European studies, it probably makes sense to encourage younger children to play outdoors and to limit screen time on near-vision devices.
The American Academy of Ophthalmology recommends that all children first be screened for myopia between ages three and five, when they are able to cooperate in ‘reading’ letters or symbols on an eye chart. The screening is usually done in the pediatrician’s office at each annual checkup, but it can also be done by an optometrist, ophthalmologist, or other trained professional. Of course, if your child is showing any signs of being nearsighted, it is important to have his or her vision checked as soon as possible.
If you are an adult with myopia, make sure to visit your eye doctor on the schedule he or she recommends, even if your eyeglass prescription seems fine. Myopia can cause complications that you might not be aware of, but these complications can often be treated if caught early. As with any medical condition, early detection is always better.
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