If you have glasses, chances are pretty good that you have been diagnosed with Nearsightedness, or myopia, as it is medically termed. This condition is found when close objects are seen clearly, but objects farther away appear blurred. Nearsightedness occurs if the eyeball is too long or the cornea, or the clear front cover of the eye, has too much curvature. As a result of these facts, the light entering the eye isn't focused correctly and distant objects do look blurred.
Nearsightedness is a very common vision condition affecting nearly 30 percent of the U.S. population. Some research supports the theory that nearsightedness is hereditary. According to leading doctors there is also growing evidence that it is influenced by the visual stress of too much close work.
In general, nearsightedness usually first occurs in school-age children. Because the eye continues to grow during childhood, it typically progresses until about age 20. However, nearsightedness may also develop in adults due to visual stress or health conditions such as diabetes.
A common sign of nearsightedness is difficulty with the clarity of distant objects like a movie or TV screen or the chalkboard in school. A comprehensive optometric examination will include testing for nearsightedness. Here at Long Vision Center, Dr. Long can prescribe eyeglasses or contact lenses that correct nearsightedness by bending the visual images that enter the eyes, focusing the images correctly at the back of the eye. Depending on the amount of nearsightedness, you may only need to wear glasses or contact lenses for certain activities, like watching a movie or driving a car. Or, if you are very nearsighted, they may need to be worn all the time.
Another option for treating nearsightedness is orthokeratology (ortho-k), also known as corneal refractive therapy. It is a non-surgical procedure that involves wearing a series of specially designed rigid contact lenses to gradually reshape the curvature of your cornea. The lenses place pressure on the cornea to flatten it. This changes how light entering the eye is focused.
Laser procedures are also a possible treatment for nearsightedness in adults. They involve reshaping the cornea by removing a small amount of eye tissue. This is accomplished by using a highly focused laser beam on the surface of the eye.
For people with higher levels of nearsightedness, other refractive surgery procedures are now available. These procedures involve implanting a small lens with the desired optical correction directly inside the eye, either just in front of the natural lens (phakic intraocular lens implant) or replacing the natural lens (clear lens extraction with intraocular lens implantation). These procedures are similar to one used for cataract surgery patients, who also have lenses implanted in their eyes (intraocular lens implants).
Testing for nearsightedness may use several procedures in order to measure how the eyes focus light and to determine the power of any optical lenses needed to correct the reduced vision.
A phoropter and retinoscope are often used to determine the lenses that allow the clearest vision during a comprehensive eye exam. And as part of the testing, letters on a distance chart are identified. This test measures visual acuity, which is written as a fraction such as 20/40. The top number of the fraction is the standard distance at which testing is performed, twenty feet. The bottom number is the smallest letter size read. A person with 20/40 visual acuity would have to get within 20 feet to identify a letter that could be seen clearly at forty feet in a normal eye. Normal distance visual acuity is 20/20, although many people have 20/15 (better) vision.
Using an instrument called a phoropter, an optometrist places a series of lenses in front of your eyes and measures how they focus light using a hand held lighted instrument called a retinoscope. The doctor may choose to use an automated instrument that automatically evaluates the focusing power of the eye. The power is then refined by patient's responses to determine the lenses that allow the clearest vision.
This testing may be done without the use of eye drops to determine how the eyes respond under normal seeing conditions. In some cases, such as for patients who can't respond verbally, or when some of the eye's focusing power may be hidden, eye drops may be used. They temporarily keep the eyes from changing focus while testing is performed.
Using the information obtained from these tests, along with the results of other tests of eye focusing and eye teaming, Dr. Long can determine if you have nearsightedness. He can also determine the power of any lens correction needed to provide clear vision. Once testing is complete, a member of our staff can discuss options for treatment.