Myopia

Definition
Myopia, commonly known as nearsightedness, is a condition that affects vision. A person with myopia can see objects nearby, but has difficulty clearly focusing on objects in the distance.

Causes/associated factors
With normal vision, light enters the cornea (the clear surface covering the eye) and then strikes the lens of the eye. From there, the light is bent or refracted toward the retina in the back of the eye. The image from the retina is transmitted to the brain by the optic nerve. With myopia, the light rays focus in front of the retina instead of on it, causing the images to be blurred.



Myopia is an inherited trait usually first noticed by age 10. It progresses at different rates. Changes in the length of the eye during growth spurts may require frequent changes in eyeglass or contact lens prescriptions. The condition may worsen as the person grows during adolescence, and then level off in adulthood. Between ages 20 and 40, vision tends to remain the same.


Signs/symptoms
The most common symptoms of myopia are blurred distance vision, squinting to see distant objects and headaches. The signs may not be noticed right away, especially if the onset is slow or only one eye is affected. Children often do not complain of vision problems.

Diagnosis
Myopia is diagnosed through an eye exam. You'll be asked to read an eye chart from a distance of 20 feet. You may also look through several corrective lenses to see which make your vision the clearest.

Treatment
Treatment is usually corrective lenses, either eyeglasses or contact lenses. The lenses do not reverse or cure myopia. They simply bend light rays to come into clearer focus on the retina.
Surgery
There are several surgical options designed to treat myopia. With each procedure, the doctor reshapes the cornea to improve vision. This type of eye surgery is usually done on an outpatient basis using a topical anesthetic, which only numbs the eyes. Remember that all surgical procedures have risks, benefits and side effects. Not all people are considered good candidates for surgical correction of myopia. Discuss all of these issues with your ophthalmologist before surgery, and make sure the doctor who does the surgery has extensive experience in the particular type of surgery and uses equipment approved by the U.S. Food and Drug Administration.

Eximer laser photorefractive keratectomy (PRK): With eximer laser photorefractive keratectomy (PRK), the surgeon uses uses a laser to remove and flatten the tissue of the cornea. Antibiotic eyedrops given before surgery help prevent infection during recovery. The procedure takes about 15 minutes. After surgery, you will wear a contact lens bandage for three to five days. Anti-inflammatory eye drops and pain medication are often prescribed.
Benefits: Vision typically stabilizes within three months after surgery. Most people don't need to wear glasses or contacts after surgery.

Risks: Problems with glare or halos around lights are common after surgery. For most people, these symptoms decrease or disappear within six months. Long-term studies are not yet available. This procedure is not recommended for anyone who has an autoimmune disease (a condition in which the body produces antibodies to fight against its own tissues) or glaucoma (an eye disease in which the optic nerve is damaged). Also, it may not be recommended if you have severe myopia.


Laser in-situ keratomileusis (LASIK): Laser in-situ keratomileusis has now largely replaced PRK in the United States. The surgeon first uses a knife called a microkeratome to cut a flap of tissue from the cornea. Then, an excimer laser is used to remove a thin layer of tissue from under the flap. The flap is then replaced. Because LASIK flattens the central area of the cornea, it can be used for severe myopia. Your doctor will decide if both eyes may be operated on at the same time. Some doctors choose to wait a few days to several weeks between operations to evaluate the outcome of the first eye. LASIK has become extremely popular in the United States.
Benefits: LASIK typically has a faster recovery time than PRK. Most people have good vision within days to a week.

Risks: Distortion, damage or loss of the hinged flap of tissue on the cornea are possible. It's essential to discuss with the laser eye physician whether you're a good candidate for LASIK and to understand the risks.


Radial keratotomy (RK): Radial keratotomy is rarely done anymore. With RK, the surgeon uses a series of precise microscopic incisions to flatten the cornea so that light rays are better focused on the retina to produce clearer vision. The procedure takes about 10 to 15 minutes. Mild pain or discomfort is expected for the first 48 hours after surgery.
Benefits: Those who are younger and have less significant degrees of myopia tend to have better results with RK. Most people don't need to wear glasses or contacts after the procedure.

Risks: Glare or seeing halos around lights, particularly at night, may develop after surgery and sometimes lasts for more than a year. The surgery weakens the cornea and increases the risk for eye rupture after trauma, but serious complications after radial keratotomy are rare.

Surgical side effects
Possible side effects for these surgical procedures include:

irregular astigmatism (blurred vision)
glare
overcorrection
undercorrection, which may require more surgery
inability to wear contacts
scarring of the cornea
infection
delayed healing
vision loss (more than baseline loss)
halo effect
for LASIK, flap distortion or damage

Complications
People who have severe myopia are at increased risk of holes in the macula (the small area in the center of the retina) and retinal detachment (complete or partial separation of the retina from the choroid, the membrane between the white part of the eye and the retina). The reason for the higher risk is unknown. Visual flashes, a sudden onset of "floaters," or the feeling of a curtain pulling down over your eyes may indicate retinal detachment. If you notice these symptoms, contact your ophthalmologist right away. The problem is treatable if caught early.

Pregnancy-specific information
You may find that your vision changes during pregnancy. You may experience a loss in visual clarity, probably due to fluid retention in the eye. Since vision changes may indicate something more serious, be sure to mention them to your health care provider. Because eye refraction might change during pregnancy, refractive eye surgery of any kind is usually avoided during this time.

Senior-specific information
Sclerotic (hardening) changes that increase the index of refraction in the lens are a common cause of myopia for older adults. To detect eye disorders, some experts recommend eye exams every one to two years beginning at ages 60 to 65.

Prevention
There are many unproven theories about how to slow the progression or development of myopia. Some believe behavioral or functional factors contribute to myopia, such as excessive up-close activities or mental strain. The impact of nutrition and diet is also under speculation. If you have questions or concerns about these or other factors affecting your vision, consult your doctor.
To take care of your eyes, avoid eyestrain. Use bright light for reading or other close-up activities, and wear your corrective lenses. Follow your doctor's advice regarding periodic eye exams, and notify your doctor if you develop other problems or need a stronger prescription.