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What is the Definition of Myopia?

Views: 2137
Reviewed by Nymark M, PhD on November 1, 2016

Myopia, or shortsightedness, is one of the most commonly diagnosed eye conditions in the world. People with myopia see objects in the distance as being blurred, while not having problems seeing objects nearby. It is believed that about one in three people are affected by this, and the percentage is increasing. In fact, the National Eye Institute has recently released information that showed that, between 1971 and 1972, 25% of people in this country aged between 12 and 54 were myopic, but this has increased to 41.6% between 1999 and 2004.

Signs and Symptoms of Myopia

Most people start to develop myopia around puberty, and it gets worse until the eye is fully developed. Sometimes, it starts at a younger age. Parents should always be vigilant and make sure that they monitor their children, therefore, for signs such as:

  • Needing to move to the front of the class because they cannot see what is written on the board.
  • Wanting to sit very close to the television.
  • Complaining of having tired eyes or headaches.
  • Rubbing their eyes regularly.

People with myopia will find that they struggle to see distant objects clearly, or to read road signs. However, computer use or reading does not cause any problem. Before people are diagnosed and have refractive correction, they often have headaches and eye strain, as well as feeling tired after strenuous activities.

Testing for Myopia

If you believe you or your child has myopia, you should visit your local optician or optometrist and have it tested. You should do this, as an adult, every two years, but if you have concerns, you can do it sooner as well. During this test, an optometrist will determine what your refractive error is, and possibly provide you with a prescription for eyeglasses or contact lenses.

Causes of Myopia

The main cause of myopia is that the eye grows to be marginally too long. At other times, the lens and/or cornea is too curved when compared to the eyeball’s length. Sometimes, all these causes are present. Whatever the cause, it means that light doesn’t properly focus on the retina. Instead, it is focused at the front of the retina, which means anything in the distance is blurred. Scientists don’t really know why myopia happens, although genetic factors seem to be at play. Additionally, children who spend a lot of time reading books or watching computers are at increased risk of developing it. This is another reason why playing outside is so important.

Treatment for Myopia

There are four main treatment strategies for myopia:

  1. Wearing corrective lenses, be they eyeglasses or contacts
  2. Having laser eye surgery, which is not suitable for those whose eyes are still developing
  3. Orthokeratology
  4. Artificial implants

Most people choose to have glasses or contacts, which they may or may not need to wear all the time depending on the severity of their myopia. The prescription for someone with myopia starts with a minus (-) sign, followed by a number. The higher the number, the blurrier distant objects will appear.

Refractive surgery is increasing in popularity because it can completely eliminates the need for glasses. Usually, this surgery is performed using an excimer laser, with two procedures being mainstream:

  1. PKR surgery, whereby a part of the corneal tissue is removed, allowing for more accurate focus of light on the retina.
  2. LASIK surgery, which is the most common form, whereby a thin flap on the cornea’s surface is created, after which some of the corneal tissue is removed, before the flap is placed back.

Orthokeratology is also possible, although not very common. In this procedure, you wear rigid gas permeable (RGP) lens while you sleep, which reshapes the cornea. The lens is removed in the morning, after which the cornea will hold its new shape for a set time period, meaning you do not need to wear glasses during the day. This procedure is known as corneal refractive therapy and is highly effective, but only for mild to moderate myopia, and only as a temporary solution. It may be suitable for those who are not able to have PKR or LASIK surgery.

Phakic intraocular lenses (IOL) are implantable lenses, which are very beneficial for those with high myopia, or whose cornea is thinner than normal. In that case, the chance of complications from LASIK is too high, which means they are not suitable candidates. Phakic IOLs are similar to contact lenses, but they are surgically inserted into the eye and are permanent. They are different from the ones used in cataract surgery, because they do not actually replace the natural lens of the eye itself.

Eye Conditions Associated with Myopia

Some people who have severe myopia, and particularly children who have myopia that has been left untreated, are more likely to also have other eye problems. These include:

  • Squints, which is particularly common in children. Here, the two eyes point in different directions.
  • Lazy eyes, again more common in children. Here, the vision in one of the eyes does not develop properly.
  • Glaucoma, which is more common in adult and elderly people, leads to pressure building up inside the eye. This is a medical emergency and requires treatment.
  • Cataracts, which are also more common in adults and the elderly. Here, cloudy patches are found in the lens, disturbing vision. It is easily corrected using surgery.
  • Retinal detachment, which is a serious medical emergency. Here, the retina has been detached from its blood supply, meaning it is starved of nutrients and oxygen.

How to Control Myopia

Because so many people now are myopic, scientists are very interested in finding a way to stop it from progressing during childhood. There has been a lot of research in various techniques, including providing children with gas permeable contact lenses, progressive lenses, and bifocals. So far, the results have been mixed at best.

Scientists from New Zealand have tested dual focus soft contact lenses, and they have had promising results in nearsighted children. These lenses, which are still in the experimental stage, are not as powerful in the periphery compared to the center. This is known as peripheral defocus and scientists now believe that these lenses may lower the chance of the eye becoming too lengthy, which is a common precursor of myopia.

The study was released in 2011 and indicated that 70% of the test subjects, all aged between 11 and 14, had a 30% reduction of myopia in the eye in which they wore the experimental lens compared to the eye in which they wore a standard contact lens. Unfortunately, these lenses are not yet available in the mainstream market. However, research has commenced to determine whether the effects can be replicated on a larger group of young people. If clinical trials are successful and similar results are observed, it is likely that they will soon not just become available, but that they will be covered by medical insurance companies as well.

Degenerative Myopia

Most of the time, myopia is nothing more than an inconvenience. There are no risks associated with it in terms of the eye’s health. However, there are rare cases in which myopia is incredibly progressive and severe. This is known as degenerative myopia, pathological myopia, or malignant myopia. It is rare and believed to be related to genes, as it usually starts in early childhood. It affects around 2% of the population and is one of the main causes of legal blindness in this country.

For people who have degenerative myopia, their eyeball becomes elongated rapidly. This means that the myopia progresses quickly and severely, often leading to full loss of vision. People who have malignant myopia are also at a greater risk of experiencing retinal detachment, as well as various other degenerative problems at the back of the eye. There is the possibility of neovascularization, which happens when abnormal blood vessels start to grow and bleed. The risk of cataracts is also increased.

For those who are diagnosed with pathological myopia, they will usually be offered a surgical procedure known as photodynamic therapy, together with medication. This type of laser therapy is commonly used on people who have macular degeneration.

Meanwhile, scientists have recently completed a study showing that oral application of 7-mx (7-methylxanthine) slows down the rate at which the eye elongates in children between age 8 and 13. This means that there may be a solution for those who are known to be at risk of degenerative myopia, and that appropriate treatment could be found soon as well.

Resources and References:

Mayo Clinic – Information on Nearsightedness (Mayoclinic.org)

American Academy of Ophthalmology – Nearsightedness: What Is Myopia? (AAO.org)

National Eye Institute – Facts about Myopia (NIH.gov)