Myopia or nearsightedness is a common refractive error in which a person cannot see distant objects clearly. In most cases the problem is caused by an abnormally long eyeball, a steeply curved cornea, an overly thick lens, or a combination of all three factors. The length of the eyeball or curvature of the cornea or lens causes images to be focused in front of the retina (the light-sensitive tissue at the back of the eye) rather than on it. People with myopia not only need prescription lenses for nearsightedness when they are young but may also require bifocals as they age because the eye gradually loses its ability to accommodate (change focus) as a person gets older.
Myopia is a common refractive error worldwide, although the rates vary from country to country and from age group to age group. According to a British medical journal, the prevalence of myopia (including mild cases that do not require the person to wear glasses) has been reported as high as 70–90 percent in East Asia and Japan, 30–40 percent in Europe and the United States, and 10–20 percent in Africa. It is estimated that 44 percent of Japanese and Taiwanese adults have myopia severe enough to require corrective lenses, whereas in India, the rate is 7 percent of the general adult population. A study of British university students showed that 50 percent were myopic, whereas the rate of myopia in Greek university students is 37 percent. In the United States, the rate of myopia in the general population severe enough to require corrective lenses is thought to be between 20 and 25 percent. Although a few children are born with myopia, the condition is most likely to appear between ages five and twenty. About 25 percent of Americans in this age group are nearsighted. About 26 percent of people in the United States between the ages of twelve and fifty-four have myopia severe enough to require correction. Ethnicity makes a difference in rates of nearsightedness in the United States. About 78 percent of Asian Americans have myopia, followed by Hispanics (13 percent), African Americans (7 percent), and Caucasians (5 percent). As far as is known, myopia is equally common in men and women.
Nursing Care Plan Signs and SymptomsMyopia is thought to result from a combination of genetic factors and close visual work over an extended period of time in childhood. Myopia is known to run in families. In addition, the different rates of myopia among different races and ethnic groups points to some kind of genetic cause. More recently, the PAX6 gene on chromosome 11 has been identified as a gene that appears to affect the length of the human eyeball. Some doctors refer to the development of myopia in the elementary grades as school myopia, as the close work involved in learning to read and write appears to trigger nearsightedness in about 10 percent of children in the United States. The symptoms of myopia often emerge during a child’s first years in school. Parents may notice that the child holds a book very close while reading or leans close to the desk surface while writing. He or she may squint a lot or sit very close to the television or blackboard. Other symptoms include headaches and failure to notice distant objects.
Nursing Care Plan DiagnosisMyopia and other refractive errors are evaluated by a series of vision tests. After the examiner takes a history of the patient’s symptoms (including a family history of eye problems), the patient is usually asked to read the letters on an eye chart known as a Snellen chart. Each eye is tested separately. The examiner may also shine lights into the eyes or administer eye drops that allow him or her to see all the structures inside the eye clearly. This part of the examination allows the doctor to evaluate the severity of the patient’s nearsightedness. To measure the strength of the lens needed to correct the patient’s myopia, the examiner uses a device called a photopter (or refractor). The photopter is placed in front of the patient’s eyes and the examiner moves various lenses in and out of the device while the patient rereads the letters on the Snellen chart. The photopter can also be used to measure the correction needed for a bifocal lens.
Nursing Care Plan TreatmentVery mild myopia may not need corrective treatment. A person should see an eye doctor, however, if he or she is developing headaches or eye strain, or if blurry vision is interfering with daily activities. People whose nearsightedness is severe enough to require correction have several options:
• Eyeglasses. These can be used to correct nearsightedness caused by uneven curvature of the lens or cornea as well as the length of the eyeball. Eyeglasses are prescribed by an optometrist or ophthalmologist but made and fitted by an optician.
• Hard contact lenses. These usually provide more effective correction of nearsightedness than soft contact lenses.
• Orthokeratology (Ortho-K). This is a procedure in which the person wears hard contact lenses for several hours overnight in order to gradually correct the curvature of the cornea. The lenses are removed during the day. Ortho-K is also referred to as corneal molding. It does not permanently improve vision. If the patient stops wearing the retainer lenses, his or her vision may return to its original condition. Ortho-K, however, is ineffective in correcting myopia caused by an abnormally long eyeball.
• Laser Eye surgery. If a person’s nearsightedness is related to the shape of the cornea, an ophthalmologist can use lasers to reshape the cornea either by making a flap in the surface of the cornea and reshaping the tissue of the cornea under the flap, or by completely removing the upper layer of tissue in the cornea before reshaping the lower layers of tissue.
• Lens implantation. Lens implantation is a controversial treatment for moderate or severe myopia. The ophthalmologist surgically inserts a clear corrective lens inside the eye in front of the natural lens. The procedure was not performed very frequently in the early 2000s, however, because it has a high risk of complications.
There are drawbacks to surgical correction of refractive errors. These include the risks of infection, development of haze in the cornea, or dry eyes. In some cases the surgeonmay need to performa second operation if the first one either overcorrected or undercorrected the shape of the patient’s cornea. It is important for a patientwith myopia to discuss all the treatment options with the optometrist or ophthalmologist, as no two people have exactly the same degree of visual blurring or the same lifestyle. In addition, patients with diabetes require very careful evaluation before any type of laser eye surgery because diabetes weakens the retina of the eye and increases the risk of glaucoma.
Nursing Care Plan PrognosisThe prognosis of myopia depends partly on its severity. People with any degree of myopia can have their vision corrected satisfactorily by eyeglasses, contact lenses, or surgery. People with severe myopia (about 30 percent of nearsighted patients), however, have an increased risk of retinal disorders and glaucoma after age forty. They should therefore schedule regular eye examinations to reduce the risk of these complications.
Myopia is still largely considered a matter of heredity and cannot be prevented by any method known. There have been various attempts to slow the progression of nearsightedness in schoolchildren by eye exercises or such alternative therapies as biofeedback, but none have proved to be successful. People can, however, live comfortably with nearsightedness by visual screening in childhood, regular eye checkups at all ages, and wearing corrective lenses when needed.
Nearsightedness is such a common refractive error in the general population that it is not likely to disappear in the near future. It is possible that the present variety of treatment optionswill be improved or expanded by further research.