Dictionary:
my·o·pi·a (mī-ō'pē-ə)  |
[Greek muōpiā, from muōps, muōp-, nearsighted : mūein, to close the eyes + ōps, eye.]
myopic my·op'ic (-ŏp'ĭk, -ō'pĭk) adj.| 5min Related Video: myopia |
| Wordsmith Words: myopic |
(my-OP-ik)
adjective
1. Nearsighted; unable to see distant objects clearly.
2. Shortsighted; lacking foresight; narrow-minded.
Etymology
Via Latin, from Greek myopia, from myop- (nearsighted), from myein (to close) + ops (eye)
| Alternative Medicine Encyclopedia: Myopia |
Definition
Myopia is the medical term for nearsightedness. People with myopia see objects more clearly when they are close to the eye, while distant objects appear blurred or fuzzy. Reading and close-up work may be clear, but distance vision is blurry.
Description
Myopia affects about 30% of the population in the United States. To understand myopia it is necessary to have a basic knowledge of the main components involved in the eye's focusing system: the cornea, lens, and retina. The cornea is a tough, transparent, dome-shaped tissue that covers the front of the eye (not to be confused with the white, opaque sclera). The cornea lies in front of the iris (the colored part of the eye). The lens is a transparent, double-convex structure located behind the iris. The retina is a thin membrane that lines the rear of the eyeball. Light-sensitive retinal cells convert incoming light rays into electrical signals that are sent along the optic nerve to the brain, which then interprets the images. In people with normal vision, parallel light rays enter the eye and are bent by the cornea and lens (a process called refraction) to focus precisely on the retina, providing a crisp, clear image. In the myopic eye, the focusing power of the cornea (the major refracting structure of the eye) and the lens is too great with respect to the length of the eyeball. Light rays are bent too much, and they converge in front of the retina. This results in what is called a refractive error. In other words, an overly focused, fuzzy image is sent to the brain.
There are many types of myopia. Some common types include:
By far the most common, physiologic myopia develops sometime between the ages of five to 10 years and gradually progresses until the eye is fully grown. This may include refractive myopia (cornea and lens-bending properties are too strong) and axial myopia (the eyeball is too long). Pathologic myopia is a far less common abnormality. This condition begins as physiologic myopia, but rather than stabilizing, the eye continues to enlarge at an abnormal rate (progressive myopia). This more advanced type of myopia may lead to degenerative changes in the eye, or degenerative myopia. Acquired myopia occurs after infancy. This condition may be seen in association with uncontrolled diabetes and certain types of cataracts. Antihypertensive drugs and other medications can also affect the refractive power of the lens.
Causes & Symptoms
Myopia is said to be caused by an elongation of the eyeball. This means that the oblong (as opposed to normal spherical) shape of the myopic eye causes the cornea and lens to focus at a point in front of the retina. A more precise explanation is that there is an inadequate correlation between the focusing power of the cornea and lens and the length of the eye.
Myopia is considered to be primarily a hereditary disorder, meaning that it runs in families. People are generally born with a small amount of hyperopia (farsightedness), but as the eye grows this decreases and myopia does not become evident until later. Because of this, it is sometimes argued that myopia is not inherited, but acquired. Some eyecare professionals believe that a tendency toward myopia may be inherited, but the actual disorder results from a combination of environmental and genetic factors. Environmental factors include close work, stress, and eye strain.
The symptoms of myopia are blurred distance vision, eye discomfort, squinting, and eye strain.
Diagnosis
The diagnosis of myopia is typically made during the first several years of elementary school when a teacher notices a child having difficulty seeing the chalkboard, reading, or concentrating. The teacher or school nurse often recommends an eye exam by an ophthalmologist or optometrist. An ophthalmologist—M.D. or D.O. (Doctor of Osteopathy)—is a medical doctor trained in the diagnosis and treatment of eye problems. Ophthalmologists also perform eye surgery. An optometrist (O.D.) diagnoses and manages and/or treats eye and visual disorders. In many states, optometrists are licensed to use diagnostic and therapeutic drugs.
A patient's distance vision is tested by reading letters or numbers on a chart posted a set distance away (usually 20 ft, or 6 m). The doctor has the patient view images through a variety of lenses to obtain the best correction. The doctor also examines the inside of the eye and the retina. An instrument called a slit lamp is used to examine the cornea and lens. The eyeglass prescription is written in terms of diopters (D), which measure the degree of refractive error. Mild to moderate myopia usually falls between -1.00D and -6.00D. Normal vision is commonly referred to as 20/20 to describe the eye's focusing ability 20 ft away from an object. For example, 20/50 means that a myopic person must be 20 ft away from an eye chart to see what a normal person can see at 50 ft (15 m). The larger the bottom number, the greater the myopia.
Treatment
Nutritional Therapy
The following nutritional supplements may help improve vision:
Eye Exercises
Some eye care professionals recommend exercises to help improve circulation, reduce eye strain, and relax the eye muscles. The Bates method is a common set of exercises. It is possible that by combining exercises with changes in behavior, the progression of myopia may be slowed or prevented. Alternative treatments include: visual therapy (also referred to as vision training or eye exercises); discontinuing close work; reducing eye strain (taking a rest break during periods of prolonged near vision tasks); and wearing bifocals to decrease the need to accommodate when doing close-up work.
Acupuncture
Acupuncture, by acting on eye muscles, causes changes in the shape of the eyeball and thus, may be able to correct nearsightedness. Approximately 10 sessions followed by daily eye exercises are needed to see significant and prolonged results.
Allopathic Treatment
People with myopia have three main options for treatment: eyeglasses, contact lenses, and for those who meet certain criteria, refractive eye surgery.
Eyeglasses
Eyeglasses are the most common method used to correct myopia. Concave glass or plastic lenses are placed in frames in front of the eyes. The lenses diverge the light rays so they focus further back, directly upon the retina, producing clear distance vision.
Contact Lenses
Contact lenses are a second option for treatment. Contact lenses are extremely thin round discs of plastic that are worn on the eye in front of the cornea. Contact lenses offer several benefits over glasses, including: better vision, less distortion, clear peripheral vision, and cosmetic appeal. In addition, contacts don't steam up from changes in temperature or perspiration.
Refractive Eye Surgery
Recommended for people who find glasses and contact lenses inconvenient and uncomfortable, refractive eye surgery improves myopic vision by permanently changing the shape of the cornea so light rays focus properly on the retina. These procedures are performed on an outpatient basis and generally take 10-30 minutes. There are three types of corrective surgeries available as of 1998: (1) radial keratotomy, (2) photorefractive keratectomy, and (3) laser-assisted in-situ keratomileusis (LASIK). Each of these surgery techniques changes rapidly in price and effectiveness. Patients should investigate the procedures and ask many questions of their doctors or others who have had the procedures before having them done.
RADIAL KERATOTOMY. Radial keratotomy (RK), the first of these procedures made available, is considered the riskiest. The surgeon uses a delicate diamond-tipped blade, a microscope, and microscopic instruments to make several spoke-like, "radial" incisions in the nonviewing (peripheral) portion of the cornea. The slits surgically alter the curve of the cornea, making it flatter, which may improve the focus of images onto the retina.
PHOTOREFRACTIVE KERATECTOMY. Photorefractive keratectomy (PRK) involves the use of a computer to measure the shape of the cornea. Using these measurements, the surgeon applies a computer-controlled laser to make modifications to the cornea. The PRK procedure flattens the cornea by vaporizing small amounts of tissue from the cornea's surface. Photorefractive keratectomy can be used to treat mild to moderate forms of myopia. The cost is approximately $2,000 per eye.
LASER-ASSISTED IN-SITU KERATOMILEUSIS. Laserassisted in-situ keratomileusis (LASIK) is the newest of these procedures. It is recommended for moderate to severe cases of myopia. A variation on the PRK method, LASIK uses lasers and a cutting tool called a microkeratome to form a circular flap on the cornea. The flap is flipped back to expose the inner layers of the cornea. The cornea is treated with a laser to change the shape and focusing properties, then the flap is replaced.
Myopia treatments under research include corneal implants and permanent, surgically placed contact lenses.
Expected Results
Glasses and contact lenses can (but not always) bring vision to 20/20. Refractive surgery can make permanent improvements for the right myopic candidate. Ophthalmologists continue to improve upon and develop new techniques to correct myopia. Alternative treatments have not been widely studied.
Prevention
Myopia is generally considered a hereditary condition, which means that it runs in families. From this perspective there is nothing that can be done to prevent this disorder. However, because the percentage of people with myopia in the United States has steadily increased over the last 50 years, some believe that the condition results from a combination of genetic and environmental factors. If this is true, then it may be possible to prevent or control myopia by reducing close work, reading and working in good light, maintaining good nutrition, and practicing visual therapy (when recommended). In fact, a 2002 study showed that children's diets high in starches may be adding to the high prevalence of myopia. Diets high in refined starches from breads and cereals increase insulin levels, which in turn affect development of the eyeball. Increasing protein consumption has been shown to slow the progression of myopia in children.
Eye strain can be prevented by using sufficient light for reading and close work, and by wearing corrective lenses as prescribed. Everyone should have regular eye exams to see if the prescription has changed or if any other problems have developed. This is particularly important for people with high (degenerative) myopia who may be at a greater risk of developing retinal detachments or other problems.
Resources
Books
Birnbaum, Martin H. Optometric Management of Nearpoint Vision Disorders. Boston: Butterworth-Heinemann, 1993.
Curtin, Brian J. The Myopias: Basic Science and Clinical Management. Philadelphia: Harper & Row, 1985.
Rosanes-Berrett, Marilyn B. Do You Really Need Eyeglasses? Barrytown, NY: Station Hill Press, 1990.
The Burton Goldberg Group. "Vision Disorders." Alternative Medicine: The Definitive Guide. Tiburon, CA: Future Medicine Publishing, Inc., 1999.
"Vision Disorders." Reader's Digest Guide to Medical Cures & Treatments. Canada: The Reader's Digest Association, Inc., 1996.
Zinn, Walter J., and Herbert Solomon. Complete Guide to Eye-care, Eyeglasses, and Contact Lenses. Hollywood, FL: Lifetime Books, 1996.
Periodicals
Carey, Benedict. "Goodbye Glasses: New Surgery Can Deliver Sharp Vision to the Nearsighted-Without a Single Cut of the Scalpel (Photorefractive Keratotomy)." Health 10 (September 1996): 46.
"Catching Your Eye (Photorefractive Keratotomy Evaluation.)" People's Medical Society Newsletter 15 (August 1996): 6.
Fox, Douglas." Blinded by Bread: Are Diets High in Starch Making Kids Short-Sighted?." New Scientist (April 6, 2002):9–11.
"Insight on Eyesight: Seven Vision Myths: Blind Spots About Vision Can Cause Needless Worry, Wasted Effort, and Unnecessary Treatment." Consumer Reports on Health 9 (April 1997): 42.
"9 Ways to Look Better: If You Want to Improve Your Vision—Or Just Protect What You Have—Try These Eye Opening Moves." Men's Health 13 (Jan.-Feb. 1998): 50.
Schwartz, Leslie. "Visionquest (Use of Lasers in Treatment of Nearsightedness or Myopia)." Shape 16 (March 1997): 28.
Organizations
American Academy of Ophthalmology. P.O. Box 7424, San Francisco, CA 94120-7424. (415) 561-8500. http://www.eyenet.org.
American Optometric Association. 243 N. Lindbergh Blvd., St. Louis, MO 63141. (314) 991-4100. http://www.aoanet.org.
Myopia International Research Foundation. 1265 Broadway, Room 608, New York, NY 10001. (212) 684-2777.
National Eye Institute. NIH Bldg. 31, 9000 Rockville Pike, Bethesda, MD 20892. (301) 496-5248. http://www.nei.nih.gov.
[Article by: Mai Tran; Teresa G. Odle]
| Children's Health Encyclopedia: Myopia |
Definition
Myopia, or nearsightedness, is a condition in which objects in the distance are blurred either because the eye is too long or too strong. It is the result of both environmental and genetic factors.
Description
The degree to which one is myopic depends on the powers of the cornea and the lens of the eye and the length of the eyeball. In a normal eye the incoming visual images meet on the retina in the back of the eye. If these visual images converge in front of the retina instead of on the retina, then one is myopic.
There are several types of myopia, of which simple myopia is the most common. Individuals with simple myopia have eyes that are either too long or too powerful. Congenital myopia develops in infants. Individuals with high myopia, greater than six diopters, can develop pathological changes in the retina, called degenerative myopia. Nocturnal myopia, another type of myopia sometimes referred to as "night blindness," is blurred vision only in darkness. Myopia can also be induced by co-existing medical problems and drug exposure.
A child's refractive status or power of the eye when he or she begins school is a good indicator of whether the child will become nearsighted. Most children are hyperopic, or far-sighted, at birth and experience a decrease in far-sightedness throughout early childhood. Myopia is less likely to develop by age 13 if a child still has at least 0.75 diopters of hyperopia at age eight. But if a child has become at least 0.25 diopters myopic at this age then there is a 60 percent chance that the child will require spectacle correction for nearsightedness by age 13.
Myopia does decreases in later life. This appears not to be related to a decrease in close work as is often suggested but rather due to some factor intrinsically related to ageing. It has been hypothesized the power of the lens of the eye changes in later life.
High myopia has been associated with various syndromes: Ehlers-Danlos, Marfan, Down, and Stickler syndromes. Myopia is often observed in retinopathy of prematurity (ROP). ROP is seen in 68 percent of infants with low birth weights and over 80 percent of infants born with ROP will be myopic. The myopia associated with ROP increases through age five, after which it stabilizes.
Transmission
Although no gene for myopia has been isolated, heredity is believed to play a role in myopia. If both parents are myopic, then the odds that the child will be myopic are as high as 60 percent. This drops to at most 40 percent when only one parent is nearsighted, and for 15 percent of myopic children, neither parent has myopia. High myopia is especially likely to have a genetic component.
Demographics
Overall, 25 percent of those living in the United States are myopic. Myopia is slightly more prevalent among females than males, and among those with advanced academic training. Less than 5 percent of five year olds are myopic, but this percentage increases to 25 percent by late teens and to approximately 35 percent for young adults and to 42 percent of those middle-aged. These percentages decrease to 20 percent by age 65 and to less than 13 percent by age 80.
Myopia is more prevalent in Asian countries; as much as 70 percent of the Chinese population is nearsighted.
Causes and Symptoms
Congenital myopia develops because of an obstruction along the visual pathway such as cataract. The eye becomes elongated in response to blur these causes, creating a myopic eye.
A first sign that a child might have myopia is difficulty in seeing things in the distance, such as the chalkboard. The child may not see things in the distance as well as a classmate or sibling.
For the 2 percent of the population who are extremely nearsighted, an inherently weak sclera, whose fibers are not held together tightly, causes the eye to stretch. This stretching can continue into adulthood, increasing myopia.
Other causes of increasing nearsightedness include difficulty with converging, the process through which the eyes move inwardly together when reading, and esophoria, the condition in which the eyes are more comfortable positioned close to the nose. Doing a lot of close work, such as playing video games and using the computer for extended periods, may increase myopia for these children.
Causes of induced myopia include cataracts and elevations of blood sugar in diagnosed or undiagnosed diabetics. Some drugs, such as corticosteroids, antihistamines, and some antibiotics, including sulfonamides, can induce myopia.
Another cause of increasing myopia is the over wearing of contact lenses. Swelling of the cornea can occur if the eye does not have sufficient oxygen causing a transient increase in myopia. Silicone contact lenses allow a marked increase in oxygen to reach the eye decreasing the probability of myopic increases.
For the child with diabetes, fluctuations in blood sugars can cause swelling of the cornea of the eye, leading to transient increases in myopia, which stabilize once the diabetes is controlled. But the child may independently become more myopic later in life.
In the early 2000s, it has been suggested that insulin resistance, which accompanies type 2 diabetes and prediabetes, may increase myopia in children and adolescents. The level of insulin-like growth factor binding protein 3 (IGFBP-3), a hormone that works with insulin to lower blood glucose levels, is low in individuals who are insulin resistant. This decreased level, in turn, decreases the sensitivity of ocular tissue to another compound called retinoic acid, which prevents increases in the length of the eye. Thus, if insulin levels are higher than normal, the risk of myopia may be increased.
Asthenopia or a feeling of eye strain is not common in myopia. If a child complains of eye strain, then usually there is another cause of the eye strain, including an astigmatism, a condition in which the eye is football shaped; anisometropia, a condition in which the eyes are of different powers; or difficulty with focusing.
When to Call the Doctor
There are many reasons why a child cannot see well in the distance. Myopia is the most common cause of distance blur, and since much of what a child learns comes from vision and visual cues, correction of myopia is important. Also, problems with vision may be a sign of a more serious ocular problem, such as cataracts, or of a medical problem, such as diabetes.
Diagnosis
Myopia is diagnosed by determining a child's unaided vision and is confirmed objectively by the eye care practitioner with various techniques, including retinoscopy and refraction.
The type and extent of myopia is determined by additional testing. These tests include an evaluation of the child's binocular vision, his eye movements, his ability to converge and focus on objects close-up, and his ocular health. Dilation of the eye allows the doctor to check for complications of ROP, diabetes, or degenerative myopia. Since children are capable of over focusing, dilation can help the eye care practitioner determine a child's true prescription because the drugs used to dilate also impair this tendency to over focus. Over focusing can cause a child to appear to be myopic when he or she is actually not.
Treatment
Myopia is most commonly treated with spectacles or glasses. Myopia in preschool children does not need to be corrected with glasses, unless either anisometropia, a condition in which there is a difference of more than 1.00 diopters between the two eyes, or amblyopia, a condition in which a child cannot be corrected to 20/20 with spectacles, is present. As the child enters school, distance vision becomes critical for learning, and children with prescriptions of at least 1.00 diopter of myopia or who have 20/40 vision or worse should be given glasses. Once a child is diagnosed with myopia, he or she should be examined every six months to a year, and each eye should be corrected to 20/20 at each visit. The glasses are then usually worn full time, except for children with difficulty with convergence (esophoria), who may remove their glasses for close work.
Some adolescents may want to wear contact lenses. Wearing contact lenses can improve appearance. Peripheral vision is improved with contact lenses, especially for those with high degrees of myopia or who have anisometropia.
Rigid gas permeable (RGPs) contact lenses are used to correct myopia. The rate at which myopia increases may be slowed by RGP lenses. RGPs are also employed in orthokeratology, a technique in which RGP lenses of gradually decreasing flatness are worn for specified amounts of time. These lenses, called ortho-K lenses, flatten the cornea, changing the power of the cornea over time and decreasing myopia. This effect of ortho-K lenses is not permanent and an ortho-K lens must be worn periodically or the original myopia reappears. For some individuals—for example, those with keratoconnus, a disease of the cornea—RGPs may offer the only way to correct vision.
For some children the development of myopia may be slowed with reading glasses or bifocals. If bifocals are prescribed, then either progressive or no-lines, or a lined bifocal may be given. If a lined bifocal is prescribed, then the line is always placed higher for the child than for the adult. This is done to encourage use of the power of the bifocal.
Refractive surgery is also used to correct myopia, but only on fully grown individuals. A child's eyes change and the safety of these procedures have not been established in the growing eye.
The most common surgical procedure performed to correct myopia is laser in situ keratomileusis (LASIK). Other techniques to correct myopia include photorefractive keratectomy (PRK), radial keratomy (RK), laser epithelial keratomileusis (LASEK), intraocular lens implants and intrastromal corneal rings. Inflammation of the eye, increased dryness of the eye, and cataracts are some of the risks associated with refractive surgery.
Alternative Treatment
Cycloplegic drugs, such as atropine, may decrease myopia, but they may hinder the child's ability to see up close. As of 2004 pirenzepine, which has shown to decrease the rate of myopia in children without sacrificing the ability of the child to do close work, is in clinical trial.
Prognosis
Most infants are born far-sighted and eventually reach emmetropia or normal vision, by age six. Over one third of children go on to become myopic as adults.
Patients with high myopia, greater than 6.00 diopters, have an increased risk of developing a retinal tear, hole, or detachment; a posterior staphyloma; a posterior vitreous detachment; or glaucoma. Rarely are these pathological changes of myopia seen in children or adolescents. Retinal detachments and tears are possible, however, in highly myopic children or adolescents who play contact sports. If a retinal problem is diagnosed or suspected, referral to a retinal specialist is necessary.
Prevention
For individuals who have difficulty with convergence or focusing or who are esophoric, close work may increase myopia. Children diagnosed with these problems would benefit from frequent breaks while doing close work. Increases in myopia for these children may be slowed with bifocals and/or removal of glasses for reading and homework.
Nutritional Concerns
Since elevated levels of insulin may be associated with increased myopia; a diet low in those foods that increase insulin secretion, such as refined carbohydrates, may help decrease myopia.
Parental Concerns
Children rely on their vision in their learning processes; if they have difficulty seeing this handicap affects academic performance. Thus, any vision problem should be corrected promptly. Once myopia is diagnosed, it typically increases through childhood and vision correction is needed for classroom work and for sports. If a child is not corrected fully and continues to have blurred vision, the eye may elongate in response to blur, perpetuating the myopia.
Myopia cannot be diagnosed by school screenings or by simply reading eye chart at the pediatrician's office. A comprehensive eye exam as given by an ophthalmologist or an optometrist is needed, if myopia is suspected. Most cases of myopia result from changes within the eye, but the condition can be a manifestation of other more serious problems, such as cataract or diabetes.
See also Diabetes mellitus; Ehlers-Danlos syndrome; Marfan's syndrome.
Resources
Books
Cordain, Loren. The Paleo Diet. Hoboken, NJ: John Wiley & Sons, 2002.
Murillo-Lopez, Fernando H. "Myopia." In Current OcularTherapy. Philadelphia: Saunders, 2000.
Prett, Ronald C. "Pathologic Myopia." In Principles andPractice of Ophthalmology. Philadelphia: Saunders, 2000.
Steidl, Scott M., and Ronald C. Pruett. "Myopia and Systemic Disorders." In Principles and Practice of Ophthalmology. Philadelphia: Saunders, 2000.
Periodicals
Byrne, Jennifer. "Pirenzepine Showing Promise in Clinical Trials for Topical Myopia Treatment." Primary Care Optometry News 8, no. 10 (October 2003): 10–1.
Cordain, Loren, et al. "An Evolutionary Analysis of the Aetiology and Pathogenesis of Juvenile-Onset Myopia." Acta Ophthalmologica Scandinavica 80, no. 2 (April 2002): 125–35.
Karpecki, Paul M. "What's New in Refractive Surgery." Review of Optometry (May 15, 2001): 71–4.
Karpecki, Paul M., and Marc Bloomenstein. "Phakic IOLs: The LASIK Alternative." Review of Optometry (February 15, 2003): 91–2.
Mutti, Donald O., and Karla Zadnik. "Age-Related Decreases in the Prevalence of Myopia: Longitudinal Change of Cohort Effect?" Investigative Ophthalmology & Visual Science 41, no. 8 (July 2000): 2103–07.
Web Sites
"Myopia (Nearsightedness)." All About Vision. Available online at www.allaboutvision.com/conditions/myopia.htm (accessed November 30, 2004).
[Article by: Martha Reilly, OD]
| Health Dictionary: myopia |
Nearsightedness. Myopia is a visual defect in which light that enters the eye is focused in front of the retina rather than directly on it, so that distant objects appear blurred. Myopia can be corrected with eyeglasses, contact lenses, or LASIK.
| Veterinary Dictionary: myopia |
Short sightedness; light rays focus in front of the retina. The opposite of hypermetropia.
| Wikipedia: Myopia |
| Myopia | |
|---|---|
| Classification and external resources | |
| ICD-10 | H52.1 |
| ICD-9 | 367.1 |
| DiseasesDB | 8729 |
| MeSH | D009216 |
Myopia (Greek: μυωπία, muōpia, "nearsightedness"[1]), also called nearsightedness or shortsightedness, is a refractive defect of the eye in which collimated light produces image focus in front of the retina when accommodation is relaxed.
Those with myopia see nearby objects clearly but distant objects appear blurred. With myopia, the eyeball is too long, or the cornea is too steep, so images are focused in the vitreous inside the eye rather than on the retina at the back of the eye. The opposite defect of myopia is hyperopia or "farsightedness" or "long-sightedness"—this is where the cornea is too flat or the eye is too short.
Mainstream eye care professionals most commonly correct myopia through the use of corrective lenses, such as glasses or contact lenses. It may also be corrected by refractive surgery, such as LASIK. The corrective lenses have a negative optical power (i.e. are concave) which compensates for the excessive positive diopters of the myopic eye.
Contents |
Myopia has been classified in various manners.[2][3][4]
Borish and Duke-Elder classified myopia by cause:[3][4]
Various forms of myopia have been described by their clinical appearance:[4][7]
Myopia, which is measured in diopters by the strength or optical power of a corrective lens that focuses distant images on the retina, has also been classified by degree or severity:[2]
Myopia is sometimes classified by the age of onset:[2]
The global prevalence of refractive errors has been estimated from 800 million to 2.3 billion.[27] The incidence of myopia within sampled population often varies with age, country, sex, race, ethnicity, occupation, environment, and other factors.[25][28] Variability in testing and data collection methods makes comparisons of prevalence and progression difficult.[29]
In some areas, such as China, India and Malaysia, up to 41% of the adult population is myopic to -1dpt,[30] up to 80% to -0.5dpt.[31]
A recent study involving first-year undergraduate students in the United Kingdom found that 50% of British whites and 53.4% of British Asians were myopic.[32]
In Australia, the overall prevalence of myopia (worse than −0.50 diopters) has been estimated to be 17%.[33] In one recent study, less than 1 in 10 (8.4%) Australian children between the ages of 4 and 12 were found to have myopia greater than −0.50 diopters.[34] A recent review found that 16.4% of Australians aged 40 or over have at least −1.00 diopters of myopia and 2.5% have at least −5.00 diopters.[35]
In Brazil, a 2005 study estimated that 6.4% of Brazilians between the ages of 12 and 59 had −1.00 diopter of myopia or more, compared with 2.7% of the indigenous people in northwestern Brazil.[36] Another found nearly 1 in 8 (13.3%) of the students in the city of Natal were myopic.[37]
In Greece, the prevalence of myopia among 15 to 18 year old students was found to be 36.8%.[38]
In India, the prevalence of myopia in the general population has been reported to be only 6.9%.[38][39]
A recent review found that 26.6% of Western Europeans aged 40 or over have at least −1.00 diopters of myopia and 4.6% have at least −5.00 diopters.[35]
In the United States, the prevalence of myopia has been estimated at 20%.[25] Nearly 1 in 10 (9.2%) American children between the ages of 5 and 17 have myopia.[40] Approximately 25% of Americans between the ages of 12 and 54 have the condition.[41] A recent review found that 25.4% of Americans aged 40 or over have at least −1.00 diopters of myopia and 4.5% have at least −5.00 diopters.[35]
A study of Jordanian adults aged 17 to 40 found that over half (53.7%) were myopic.[42]
The prevalence of myopia has been reported as high as 70–90% in some Asian countries, 30–40% in Europe and the United States, and 10–20% in Africa.[28]
Myopia is less common in African people and associated diaspora.[25] In Americans between the ages of 12 and 54, myopia has been found to affect African Americans less than Caucasians.[41] Asians had the highest prevalence (18.5%), followed by Hispanics (13.2%). Caucasians had the lowest prevalence of myopia (4.4%), which was not significantly different from African Americans (6.6%). For hyperopia, Caucasians had the highest prevalence (19.3%), followed by Hispanics (12.7%). Asians had the lowest prevalence of hyperopia (6.3%) and were not significantly different from African Americans (6.4%). For astigmatism, Asians and Hispanics had the highest prevalences (33.6% and 36.9%, respectively) and did not differ from each other (P = .17). African Americans had the lowest prevalence of astigmatism (20.0%), followed by whites (26.4%).[43]
A number of studies have shown that the incidence of myopia increases with level of education[38][41] and many studies have shown a relationship between myopia and IQ.
According to Arthur Jensen, myopes average 7–8 IQ points higher than non-myopes. The relationship also holds within families, and siblings with a higher degree of refraction error average higher IQs than siblings with less refraction error. Jensen believes that this indicates myopia and IQ are pleiotropically related as they are caused or influenced by the same genes. No specific mechanism that could cause a relationship between myopia and IQ has yet been identified.
Also other personal characteristics, as value systems, school achievements, time spent in reading for pleasure, language abilities and time spent in sport activities correlated to the occurrence of myopia in studies.[44][45]
Because in the most common, "simple" myopia, the eye length is too long, any etiologic explanation must account for such axial elongation. To date, no single theory has been able to satisfactorily explain this elongation.
In the mid-1900s, mainstream ophthalmologists and optometrists believed myopia to be primarily hereditary; the influence of near work in its development seemed "incidental" and the increased prevalence of the condition with increasing age was viewed as a "statistical curiosity".[3][4][46]
Among mainstream researchers and eye care professionals, myopia is now thought to be a combination of genetic and environmental factors.[8][26]
There are currently two basic mechanisms believed to cause myopia: form deprivation (also known as pattern deprivation[47]) and optical defocus.[48] Form deprivation occurs when the image quality on the retina is reduced; optical defocus occurs when light focuses in front of or behind the retina. Numerous experiments with animals have shown that myopia can be artificially generated by inducing either of these conditions. In animal models wearing negative spectacle lenses, axial myopia has been shown to occur as the eye elongates to compensate for optical defocus.[48] The exact mechanism of this image-controlled elongation of the eye is still unknown.[citation needed] It has been suggested that accommodative lag leads to blur (i.e. optical defocus) which in turn stimulates axial elongation and myopia.[49]
Many people with myopia are able to read comfortably without eyeglasses even in advanced age. Myopes considering refractive surgery are advised that this may be a disadvantage after the age of 40 when the eyes become presbyopic and lose their ability to accommodate or change focus.
A diagnosis of myopia is typically confirmed during an eye examination by an ophthalmologist, optometrist or orthoptist[71]. Frequently an autorefractor or retinoscope is used to give an initial objective assessment of the refractive status of each eye, then a phoropter is used to subjectively refine the patient's eyeglass prescription.
Eyeglasses, contact lenses, and refractive surgery are the primary options to treat the visual symptoms of those with myopia. Orthokeratology is the practice of using special rigid contact lenses to flatten the cornea to reduce myopia. Occasionally, pinhole glasses are used by patients with low-level myopia. These work by reducing the blur circle formed on the retina, but their adverse effects on peripheral vision, contrast and brightness make them unsuitable in most situations.
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For people with a high degree of myopia, very strong eyeglass prescriptions are needed to correct the focus error. However, strong eyeglass prescriptions have a negative side effect in that off-axis viewing of objects away from the center of the lens results in prismatic movement and separation of colors, known as chromatic aberration. This prismatic distortion is visible to the wearer as color fringes around strongly contrasting colors. The fringes move around as the wearer's gaze through the lenses changes, and the prismatic shifting reverses on either side, above, and below the exact center of the lenses. Color fringing can make accurate drawing and painting difficult for users of strong eyeglass prescriptions.
Strongly nearsighted wearers of contact lenses do not experience chromatic aberration because the lens moves with the cornea and always stays centered in the middle of the wearer's gaze.
Practitioners and advocates of alternative therapies often recommend eye exercises and relaxation techniques such as the Bates method. However, the efficacy of these practices is disputed by scientists and eye care practitioners.[72] A 2005 review of scientific papers on the subject concluded that there was "no clear scientific evidence" that eye exercises were effective in treating myopia.[73]
In the 1980s and 1990s, there was a flurry of interest in biofeedback as a possible treatment for myopia. A 1997 review of this biofeedback research concluded that "controlled studies to validate such methods ... have been rare and contradictory."[74] It was found in one study that myopes could improve their visual acuity with biofeedback training, but that this improvement was "instrument-specific" and did not generalise to other measures or situations.[75] In another study an "improvement" in visual acuity was found but the authors concluded that this could be a result of subjects learning the task.[76] Finally, in an evaluation of a training system designed to improve acuity, "no significant difference was found between the control and experimental subjects".[77]
There is no universally accepted method of preventing myopia.[8] Commonly attempted preventative methods include wearing reading glasses, eye drops and participating in more outdoor activities are described below. Some clinicians and researchers recommend plus power (convex) lenses in the form of reading glasses when engaged in close work or reading instead of using single focal concave lens glasses commonly prescribed.[8][78] The reasoning behind convex lense's possible effectiveness in preventing myopia is simple to understand: Convex lenses's refractive property of converging light are used in reading glasses to help reduce the accommodation needed when reading and doing close work.[citation needed] For people with Presbyopia whose eye's lens can not accommodate enough for very near focus; reading glasses help converge the light before it enters the eye to complement the refractive power of the eye lens so near objects focus clearly on the retina. [1] By reducing the focusing effort needed (accommodation), reading glasses or convex lenses essentially relax the focusing ciliary muscles and may consequently reduce chances of developing myopia. source: [2] Inexpensive non prescription reading glasses are commonly sold in drug stores and dollar stores. Alternatively, reading glasses fitted by optometrists have a wider range of styles and lens choices. source: [3] A recent Malaysian study reported in New Scientist[79] suggested that undercorrection of myopia caused more rapid progression of myopia.[80] However, the reliability of these data has been called into question.[81] Many myopia treatment studies suffer from any of a number of design drawbacks: small numbers, lack of adequate control group, failure to mask examiners from knowledge of treatments used, etc.
Pirenzepine eyedrops had a limited effect on retarding myopic progression in a recent, placebo-control, double-blinded prospective controlled study.[82]
Daylight may prevent myopia. Australian researchers had concluded that exposure to daylight appeared to play a critical role in restricting the growth of the eyeball, which is responsible for myopia or short-sightedness.[83] They compared children from other developed countries such as Singapore and Australian children spent about 2–3 hours a day outdoors which could increased dopamine in the eyes that restrict distorted shaping of the eyes.[84][85][86]
Various methods have been employed in an attempt to decrease the progression of myopia.[48] Dr Chua Weihan and his team at National Eye Centre Singapore have conducted large scale studies on the effect of Atropine of varying strength in stabilizing, and in some case, reducing myopia. The use of reading glasses when doing close work may provide success by reducing or eliminating the need to accommodate. Altering the use of eyeglasses between full-time, part-time, and not at all does not appear to alter myopia progression.[87][88] The American Optometric Association's Clinical Practice Guidelines for Myopia refers to numerous studies which indicated the effectiveness of bifocal lenses and recommends it as the method for "Myopia Control".[8] In some study, bifocal and progressive lenses have not shown significant differences in altering the progression of myopia.[48]
The terms myopia and myopic (or the common terms short sightedness or short sighted) have also been used metaphorically to refer to cognitive thinking and decision making that is narrow sighted or lacking in concern for wider interests or longer-term consequences.[89] It is often used to describe a decision that may be beneficial in the present but detrimental in the future, or a viewpoint that fails to consider anything outside a very narrow and limited range (see pragmatism, which tends to be myopic). Some antonyms of short sightedness are foreseeing, "forward thinking" and prophecy. Hyperopia, the biological opposite of myopia, is also used as a metaphor for those who exhibit "far-sighted" behavior; that is, over-prioritizing long-term interests at the expense of present enjoyment.[90]
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| Translations: Myopia |
Dansk (Danish)
n. - myopi, nærsynethed
Nederlands (Dutch)
bijziendheid, kortzichtigheid
Français (French)
n. - (Méd) myopie
Deutsch (German)
n. - Myopie, Kurzsichtigkeit
Ελληνική (Greek)
n. - (παθολ.) μυωπία
Português (Portuguese)
n. - miopia (f) (Med.)
Русский (Russian)
близорукость
Svenska (Swedish)
n. - närsynthet
中文（简体）(Chinese (Simplified))
近视
中文（繁體）(Chinese (Traditional))
n. - 近視
العربيه (Arabic)
(الاسم) قصير, بصري, قصير نظر
עברית (Hebrew)
n. - קוצר-ראייה
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| Health Dictionary. The New Dictionary of Cultural Literacy, Third Edition Edited by E.D. Hirsch, Jr., Joseph F. Kett, and James Trefil. Copyright © 2002 by Houghton Mifflin Company. Published by Houghton Mifflin. All rights reserved. Read more |
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