Nearsightedness, or myopia, is the most common refractive error of the eye, and it has become more prevalent in recent years.
In fact, a recent study by the National Eye Institute (NEI) shows the prevalence of myopia grew from 25 percent of the U.S. population (ages 12 to 54) in 1971-1972 to a whopping 41.6 percent in 1999-2004.
Though the exact cause for this increase in nearsightedness among Americans is unknown, many eye doctors feel it has something to do with eye fatigue from computer use and other extended near vision tasks, coupled with a genetic predisposition for myopia.
Myopia Symptoms And Signs
If you are nearsighted, you typically will have difficulty reading road signs and seeing distant objects clearly, but will be able to see well for close-up tasks such as reading and computer use.
Other signs and symptoms of myopia include squinting, eye strain and headaches. Feeling fatigued when driving or playing sports also can be a symptom of uncorrected nearsightedness.
If you experience these signs or symptoms while wearing your glasses or contact lenses, schedule a comprehensive eye examination with your optometrist or ophthalmologist to see if you need a stronger prescription.
What Causes Myopia?
Myopia occurs when the eyeball is too long, relative to the focusing power of the cornea and lens of the eye. This causes light rays to focus at a point in front of the retina, rather than directly on its surface.
Nearsightedness also can be caused by the cornea and/or lens being too curved for the length of the eyeball. In some cases, myopia is due to a combination of these factors.
Myopia typically begins in childhood and you may have a higher risk if your parents are nearsighted. In most cases, nearsightedness stabilizes in early adulthood but sometimes it continues to progress with age.
Nearsightedness can be corrected with glasses, contact lenses or refractive surgery. Depending on the degree of your myopia, you may need to wear your glasses or contact lenses all the time or only when you need very clear distance vision, like when driving, seeing a chalkboard or watching a movie.
Good choices for eyeglass lenses for nearsightedness include high-index lenses (for thinner, lighter glasses) and anti-reflective coating. Also, consider photochromic lenses to protect your eyes from UV and high-energy blue light and to reduce your need for a separate pair of prescription sunglasses outdoors.
If you're nearsighted, the first number ("sphere") on your eyeglasses prescription or contact lens prescription will be preceded by a minus sign (–). The higher the number, the more nearsighted you are.
Refractive surgery can reduce or even eliminate your need for glasses or contacts. The most common procedures are performed with an excimer laser.
In PRK the laser removes a layer of corneal tissue, which flattens the cornea and allows light rays to focus more accurately on the retina.
In LASIK — the most common refractive procedure — a thin flap is created on the surface of the cornea, a laser removes some corneal tissue, and then the flap is returned to its original position.
Then there's orthokeratology, a non-surgical procedure where you wear special rigid gas permeable (RGP or GP) contact lenses at night that reshape your cornea while you sleep. When you remove the lenses in the morning, your cornea temporarily retains the new shape, so you can see clearly during the day without glasses or contact lenses.
Orthokeratology and a related GP contact lens procedure called corneal refractive therapy (CRT) have been proven effective at temporarily correcting mild to moderate amounts of myopia. Both procedures are good alternatives to surgery for individuals who are too young for LASIK or are not good candidates for refractive surgery for other reasons.
Implantable lenses known as phakic IOLs are another surgical option for correcting nearsightedness, particularly for individuals with high amounts of myopia or thinner-than-normal corneas that could increase their risk of complications from LASIK or other laser vision correction procedures.
Phakic IOLs work like contact lenses, except they are surgically placed within the eye and typically are permanent, which means no maintenance is needed. Unlike IOLs used in cataract surgery, phakic IOLs do not replace the eye's natural lens, which is left intact.
With more and more people getting nearsighted these days, there is a lot of interest in finding ways to control the progression of myopia in childhood.
A number of different techniques have been tried — including fitting children with bifocals, progressive lenses and gas permeable contact lenses — with mixed results.
Recently, researchers in New Zealand have reported encouraging outcomes from specially designed "dual focus" soft contact lenses for myopia control in nearsighted children. The experimental lenses have significantly less power in the periphery of the lens compared to the center, and it is thought that this "peripheral defocus" may reduce the tendency for greater lengthening of the eye that leads to progressive myopia.
In a study published in 2011, the researchers found that in 70 percent of nearsighted children (ages 11 to 14) who wore the experimental lenses in one eye and a standard soft contact lens in the other, myopia progression was reduced by 30 percent or more in the eye wearing the dual focus contact lens.
Though dual focus contact lenses for myopia control are not yet available in the United States, research is ongoing to evaluate the effectiveness of the lenses on a larger population of children.
In most cases, nearsightedness is simply a minor inconvenience and poses little or no risk to the health of the eye. But sometimes myopia can be so progressive and severe it is considered a degenerative condition.
Degenerative myopia (also called malignant or pathological myopia) is a relatively rare condition that is believed to be hereditary and usually begins in early childhood. About 2 percent of Americans are afflicted, and degenerative myopia is a leading cause of legal blindness.
In malignant myopia, the elongation of the eyeball can occur rapidly, leading to a quick and severe progression of myopia and loss of vision. People with the condition have a significantly increased risk of retinal detachment and other degenerative changes in the back of the eye, including bleeding in the eye from abnormal blood vessel growth (neovascularization).
Degenerative myopia also may increase the risk of cataracts.
Surgical treatment for complications of degenerative myopia includes a combination drug and laser procedure called photodynamic therapy that also is used for the treatment of macular degeneration.
Also, a recent pilot study found that an oral medicine called 7-methylxanthine (7-mx) was effective in slowing the elongation of the eye in nearsighted children ages 8 to 13. Studies of this type might eventually lead to an effective medical treatment for degenerative myopia.
Source: All About Vision