The National Eye Institute reports that the incidence of nearsightedness (myopia) in people ages 12-54 has increased from 25% to more than 40% since the early 1970s. People who are nearsighted have long eyes, such that when light enters the eyes, the rays focus at a point in front of the retina, which is at the back of the eye.
This is the most common refractive eye error, which is commonly associated with genetic causes and eye fatigue.
Symptoms and Signs of Myopia
People who are nearsighted typically have difficulty reading and seeing objects at a distance clearly, but are able to see better for near visual tasks such as computer work and reading. Other symptoms include eyestrain, squinting, and headaches. Nearsighted people often feel fatigued when playing sports or driving.
If you are wearing eyeglasses or contact lenses and still experiencing these symptoms, you may need a change in prescription, so you must visit your eye doctor for a comprehensive eye exam.
Causes of Myopia
Myopia is a refractive error that is caused by a long eyeball. Normally, light rays are focused on the surface of the retina. With a long eyeball, the light rays focus at a point before they reach the retina, causing blurred vision.
Myopia can also be caused by the increased curvature of the cornea (surface of the eye) and/or the lens relative to the eyeball. In some people, myopia is caused by a combination of these factors.
Myopia usually begins during childhood. People who have nearsighted parents have a higher risk of becoming nearsighted. Myopia usually stabilizes during early adulthood, although it may continue to progress with age.
Treatment of Myopia
Treatment for nearsightedness consists of using corrective eyeglasses or contact lenses. Refractive surgery is also an option. This can help reduce or eliminate the need for using eyeglasses or contact lenses.
The common refractive procedures involve the use of excimer laser. These include:
- Photorefractive keratectomy (PRK). This procedure involves removal of a layer of the cornea, which flattens it, allowing light to focus accurately on your retina.
- LASIK. This is the most common surgical procedure, which involves creating a thin flap on the cornea, using a laser to remove corneal tissue, and replacing the flap.
Implantable intraocular lenses or phakic IOLs are surgically placed in the eye to correct nearsightedness, especially for people with extreme myopia or very thin corneas, which are not suitable for laser procedures. Phakic IOLs are similar to contact lenses, although they are more permanent, needing no maintenance or care. The eyes’ natural lens are left intact.
A non-surgical procedure called orthokeratology involves wearing a special type of rigid gas permeable contact lenses at night to reshape the cornea while sleeping. When the lenses are removed in the morning, the cornea retains the new shape temporarily, enabling you to see clearly during the rest of the day without wearing contact lenses or eyeglasses.
Another alternative to surgery is corneal refractive therapy, which can temporarily correct mild to moderate myopia in people for whom refractive surgery may not be suitable.
Dual Focus Contact Lenses
Recent research in New Zealand has shown encouraging outcomes in using soft contact lenses with "dual focus," which are specially designed to control myopia in nearsighted children. These experimental lenses are designed so that there is much less power at the lens periphery compared to its center. The "peripheral defocus" is believed to reduce the tendency for the eye to lengthen, which leads to progressive nearsightedness. The use of special dual focus contact lenses is still undergoing continued research and they are not yet commercially available in the US.
A rare condition called degenerative myopia affects about two percent of Americans. This progressive condition is also called malignant myopia, and is the leading cause of legal blindness. In this condition, the eyeball elongates rapidly, which leads to increased risk of detachment of the retina, degenerative eye changes, and bleeding inside the eye. This condition also increases one’s risk for cataracts.
Complications of degenerative myopia are usually treated with a combination of drugs and photodynamic therapy, which involves a laser procedure that is also used for treating macular degeneration.
A recent study found that a drug called 7-mx (7-methylxanthine) may help slow down eye elongation in nearsighted children. Experts believe that studies of this kind may eventually lead scientists to find an effective treatment for degenerative myopia.