|A nearsighted eye is "too long," causing light to converge in front of the retina instead of on it, blurring distance vision.
Nearsightedness, medically known as myopia (my-OH-pee-uh), refers to vision that is good at close range but poor at a distance. Nearsightedness generally occurs because the eyeball is too “long” as measured from front to back – being oval-shaped instead of being spherical.
Because of the increased distance between the
cornea and retina,
light converges in front of the retina, rather than on it, making distant objects blurry. This may cause a nearsighted person to squint in order to see distant objects. Myopia comes from the Greek words myein, meaning shut, and ops, meaning eye.
Nearsightedness, also known as “shortsightedness” or “close-sightedness,” is the most common vision problem in the U.S., affecting between 25 and 40 percent of the population. It usually develops in children and teenagers during growth periods, and may require frequent changes in corrective lens prescriptions – a reason why regular eye exams are important. It usually stops progressing around age 20, when growth is completed, and may even decrease slightly through the rest of your life.
Most experts believe that nearsightedness is usually inherited, since it tends to run in families. Some believe that intense close-vision activities such as reading or computer use “stretches” the eye and may cause, and not only exacerbate, nearsightedness.
People who are nearsighted have blurred vision or difficulty focusing on “distance” objects such as road signs or a movie screen, but can clearly see “close” objects such as reading a newspaper or road map. Poor school performance is often the first clue in children, since they cannot see the blackboard. Other symptoms can include:
- Squinting to focus in the distance
- Eye strain
- Headaches can result from squinting or eye strain, especially when coupled with astigmatism.
Most cases of nearsightedness are inherited, and therefore cannot be prevented. However, its severity may be affected by poor nutrition, stress and intense close visual work under poor lighting or too much glare. When performing close visual work, keep the work area well-lit and glare-free, and take breaks every 30 minutes or so from close visual activity, and focus on distant objects to give your eyes a break.
Nearsightedness is diagnosed during a routine eye exam and usually described by a fraction number. For example, person with 20/100 vision can see at 20 feet what a person with perfect vision can see at 100 feet. Once diagnosed, your eyecare practitioner may review these treatments:
- Corrective lenses are the most popular and least invasive treatment for nearsightedness, but surgery can also be effective. If you are mildly nearsighted, your eyecare practitioner may suggest that you wear corrective lenses only for activities that require distance vision such as driving, watching a movie or participating in sports. For moderate or severe myopia, you may need corrective eyewear at all times. You will have several options:
with concave lenses, which are thinner in the center and thicker on the edges to bend light so that it converges further back in the eye to reach the retina.
- Contact Lenses. There are various options, including rigid gas-permeable (RGP) lenses, which may slow or even stop the progression of myopia because the cornea conforms to the shape of the lens. For this reason, RGP lenses are being used in a new, alternative treatment called orthokeratology in which a series of RGP lenses of varying strengths and thus, curvatures, are used to gradually reshape the cornea and place light on the retina.
- Acrylic corneal implants are small acrylic disks or rings that inserted just under the surface of the cornea to reshape the curvature and correct refraction. The implant is similar to a contact lens but eliminates the need for daily care. This is a new procedure in the United States. This procedure has several advantages over laser surgery, including the ability to change the implants multiple times, the possibility to reverse the procedure, and less modification to the cornea. The risks are similar to those of laser surgery. If side effects become pronounced, the implants may need to be removed.
- Surgery has been effective for many people with nearsightedness, but its long-term effects are still being studied. Surgery also carries the risk of side effects, including increased sensitivity to glare, seeing halos around lights, poor vision, dry eye and others. In general, surgery for nearsightedness is not recommended for those under age 18. Among the options:
- LASIK(laser in situ keratomileusis) is a procedure in which a surgeon slices a flap into the cornea and a laser removes some corneal tissue from beneath the sliced area. This helps “flatten” the cornea to improve distance vision.
- Radial keratotomy(RK) is a procedure in which tiny cuts are made into the periphery of the cornea after the eye is anesthetized, causing the central portion of the cornea to flatten.
- Photorefractive keratotomy (PRK) uses a laser beam to remove tissue from the outer surface of the cornea, reshaping it to improve its focus.