Myopia or Nearsightedness
What is Myopia?
Myopia is the medical term for nearsightedness, which is caused by a refractive error many people can be born with or develop as they age. It is not a disease, but rather a condition. Unlike farsighted individuals, who have a shorter eyeball, myopic individuals typically have a longer eyeball. People with myopia are able to see near objects clearly, while objects at greater distances seem blurry.
Several factors may play a role in the development of myopia. For example, a nearsighted person may have a longer eyeball, a steeply curved cornea, a lens that stays focused for near vision, or some combination of these factors.
Like other refractive errors, nearsightedness is measured in units called diopters. A diopter is the measure of optical lens power, which is determined by the distance from the lens surface at which light is brought into perfect focus. When looking at an eyeglass prescription, a minus sign indicates a prescription for nearsightedness, and the numbers that follow indicate the degree of nearsightedness.
- 0 = normal or emmetropic
- -0.25 to -3.00 diopters = mild nearsightedness
- -3.25 to -6.00 diopters = moderate nearsightedness
- -6.25 to -10.00 diopters = severe nearsightedness
- -10.25 diopters or higher = extreme nearsightedness
Symptoms of myopia may include:
- Distant objects seem blurry
- Children may have trouble reading a chalkboard, but can easily read a book
- Eye strain
- Worsening of symptoms over time
Causes of Myopia
Myopia may result from excessive elongation of the eye, which is not compensated for because in myopic individuals, for unknown reasons, the internal crystalline lens can no longer decrease in power by thinning and stretching. This causes images to form in front of the retina rather than on it. People with myopia see near objects clearly, but distant objects appear blurred.
Myopia is generally believed to be a result of a combination of genetic predisposition and environmental factors, such as extensive close work. Often the condition develops during childhood and continues to worsen until early adulthood. In some cases the condition stabilizes at this point due to the absence of other stress factors, or because the body is done growing. Many experts believe myopia is inherited, but studies have shown that certain professions have higher incidences of myopia. For example, one study was conducted on Navy submariners who were submerged for months at a time and spent their days in spaces where maximum viewing distance was eight feet. The study showed an increase in nearsightedness during these extended periods of confinement.
Geneticists have yet to come up with a predictable pattern for myopia. Children born to two myopic parents are at a higher risk for the condition, but some may never develop it. Other children develop the condition even though neither parent is myopic. This is where environmental factors may lead to a progression in myopia. Excessive reading, computer use, and needle-point work are common examples of external factors that may contribute to myopia.
Risk Factors for Myopia
Individuals who perform tasks that involve using the eyes on near objects, such as excessive reading or computer use, may be at a higher risk for developing myopia. Persons born to parents who are myopic are also at a higher risk. Various studies have suggested that the prevalence of myopia increases in relation to the literacy of a population. In particular, Asians have a very high incidence of nearsightedness, with some Asian countries reporting 70 to 90 percent of the population as nearsighted.
For some myopic individuals, particularly those with -6.00 diopters or more, myopia may be a risk factor for other ocular diseases and pathologies. In general, the risk of these conditions increases as the severity of the myopia increases. Based on additional factors such as your overall ocular health, your eye doctor will be better able to determine your individual risk. Ocular conditions which may be associated with myopia include:
To diagnose myopia, an eye doctor will perform a thorough eye exam, which will include tests to determine your refractive error. Myopic individuals have trouble reading a Snellen chart (the familiar chart with the big E), but can easily read the near point card.
Other tests that should be administered to a patient with myopia include:
- Tonometry (eye pressure test)
- Retinal examination
- Slit lamp examination
People with myopia usually are able to see distant objects a little better by squinting, which reduces the spherical aberration (the degree to which light striking the lens of the eye is distorted by refraction). All treatments for myopia have the same goal: to provide clearer distance vision. Eyeglasses, contacts, or surgery—or a combination of these methods—may be used to treat myopia.
Eyeglasses and contact lenses are the most common treatments for myopia. Eyeglass lenses are designed to refocus light on the retina. A negative (concave) lens with the proper prescription may correct nearsightedness. Some studies suggest that people with myopia who use a distance correction while performing close-up tasks may eventually increase the severity of their myopia. Some doctors reduce the distance correction for near tasks, which may reduce the degree of myopia that subsequently develops.
Depending on the degree of myopia, other techniques may be used. Laser assisted in-situ keratomileusis, also known as LASIK Eye Surgery, is the most popular surgery used to treat myopia. In this procedure the shape of the cornea is changed with a laser. An alternative to LASIK, photorefractive keratectomy (PRK for short), also involves reshaping the cornea.
Prognosis for Myopia
Prescriptions usually change most rapidly between the ages of 7 and 18. Some experts believe this is due to a combination of the body growing and vigorous schoolwork (i.e., excessive reading), which puts too much stress on the eye’s natural focusing system and induces myopia. Typically, myopia can be controlled and vision can be improved significantly with corrective lenses. Refractive surgery is also an option for many adults.
It is believed by some eye care professionals that we can do things to slow the progression of myopia. Although there is no conclusive proof of their efficacy, it has been suggested that the following precautions and habits may reduce the level of myopia that develops in a person:
- Keep reading material 14 to 16 inches from your eyes.
- Always make sure room lighting permits you to perform near-point tasks without eyestrain.
- Talk with a vision therapist before symptoms become severe.
- If you are at a higher risk for myopia, visit your eye doctor annually.
- If you work in front of a computer all day, take plenty of “eye breaks” throughout your day to look far away—out a window, for example.
In rare cases, myopic individuals develop additional eye problems such as retinal detachment or retinal degeneration. Myopia increases the risk of developing other ocular diseases such as glaucoma. Complications may arise after treating myopia. For example, contact lens wearers who do not take proper care of their lenses may develop corneal ulcers or infections.
Talking to Your Eye Doctor
If you or your child develops symptoms of myopia, seek medical help from an optometrist or ophthalmologist right away. While visiting the doctor, be sure to ask questions such as:
- Which treatment options would work best for me?
- Am I a good candidate for LASIK surgery?
- What are some of the complications that may arise with each type of treatment?
- What are the chances we can slow down the progression of the myopia?
- Now that I have been diagnosed with myopia, how often should I come in to see you for an examination?
- What additional symptoms should I watch for that may indicate a more serious problem?
Did you know: Approximately one out of every four Americans has myopia.
Did you know: About 1.6 percent of children entering school in the U.S. have some degree of nearsightedness.
- J. DiGirolamo, MD “The Big Book of Family Eye Care” (Basic Health Publications, 2011) 38-49
- Wilkinson PS, David EA, Hardten DR. LASIK. In: Yanoff M, Duker JS, eds. Ophthalmology. 3rd ed. St. Louis, Mo: Mosby Elsevier; 2008: chap 3.5
- J. Anshel, MD “Smart Medicine for Your Eyes” (SquareOne Publishers, 2011) 273-278
- The International Myopia Prevention Association, 2005 FDA Petition, http://www.myopia.org/fdapetition.pdf