Nearsightedness (Myopia)
Myopia, unlike normal acuity, occurs when the cornea/lens is too curved or the eye is too long. This causes light to focus in front of the retina, resulting in blurry distance vision. Reading vision is normally very good.
Myopia is a very common condition that affects nearly 30 percent of the U.S. population. It normally starts to appear between the ages of eight and 12 years old, and almost always before the age of 20. As the body grows, the condition often worsens. It typically stabilizes in adulthood.
Symptom of myopia: Blurry distance vision
Causes of myopia
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Heredity definitely plays a role but myopia can also be due to functional focusing problems - such as difficulty in maintaining near focus and other visual stressors. The brain tries to adjust and near vision becomes more comfortable with the sacrifice of distance acuity.
Nearsightedness that develops in adulthood is more likely to be the result of visual stress and may be related to eye focusing or eye coordination problems. For example, the visual stress caused by hours of daily reading and/or close work required by higher education, professional schools, or certain occupations can induce nearsightedness in some adults.
Nearsighted children often are not aware that they are not seeing as well as they should. They think that everyone sees the world just as they do. Vision problems may not become evident until they begin to have difficulty seeing the board in school or do poorly in sports.
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Diet
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Personality Type
Diagnosing myopia
Many times, myopia is diagnosed during school screenings. Sometimes parents notice that their children are having difficulty seeing street signs or the television. Dr. Mayer can conduct a refractive evaluation to determine whether your eyes focus light rays exactly on the retina at distance and near. A visual acuity test will determine your ability to see sharply and clearly at all distances. Dr. Mayer will also check your eye coordination and muscle control, as well as your eyes' ability to change focus. All of these are important factors in how your eyes see.
Treatment of myopia
Generally includes the use of prescription eyeglasses or contact lenses to restore clear distance vision. In some cases -- with either children or adults -- special single focus or bifocal lenses are recommended to help (1) reduce visual stress from close activities, and (2) prevent or slow the progression of nearsightedness. Bifocals can definitely be a help for many, especially those that have a tendency for their eyes to cross (esophoria).
In some cases, problems with eye focusing, eye coordination, or visual function can contribute to the development or progression of nearsightedness. In such cases, a program of Vision Therapy can be used to slow the progression or reduce the severity of nearsightedness. Vision Therapy is used to treat both children and adults.
Accelerated orthokeratology can be another means of reducing myopia.
For adults, a number of laser and other surgical procedures are also available to reduce reliance on eyeglasses or contact lenses.
Good visual hygiene, including reading with good posture, using good lighting, and taking frequent short breaks during reading or any other close activity, are considered to be helpful in preventing or reducing the progression of myopia, particularly in children. Diet and supplements can also help.
Etiology - Scientific References for what causes myopia?
Goldschmidt E - "The mystery of myopia" Acta Ophthalmol Scand 81(5):431-6 (2003) LINK
- ”The aetiology of myopia is multifactorial and both genes and environment play important roles. Twin studies indicate a strong genetic influence and a weak environmental impact, while extreme myopia prevalences among selected population groups (university students) point to the opposite.”
Feldkamper M, Schaeffel F - "Interactions of genes and environment in myopia" Dev Ophthalmol 37:34-49 (2003) LINK
- "There is no doubt that an environmental component is involved and extended near work appears to be the major risk factor....A number of systemic or ophthalmic diseases are associated with myopia, indicating that metabolic conditions may interfere either with the gains of the feedback loops or the responses of the target tissue, the sclera."
Genetics?
Morgan IG - "The biological basis of myopic refractive error" Clin Exp Optom 86(5):276-88 (2003) FULL TEXT
"...in countries where the prevalence of myopia has rapidly increased to 80 to 90 per cent in young adults, it is clearly not simple genetic determination that leads to myopia. The prevalence is changing so fast that many young Asians are now myopic without any family history of myopia."
Goh WS, Lam CS - "Changes in refractive trends and optical components of Hong Kong Chinese aged 19-39 years" Ophthalmic Physiol Opt.4(4):378-82 (1994) LINK
"The prevalence of myopia in the Chinese population seems to be a new trend for the younger Hong Kong Chinese when compared with adults aged over 40 years. Thus the importance of genetics in determination of myopia is called into question by these findings."
Lam CS, Goh WS, Tang YK, Tsui KK, Wong WC, Man TC - "Changes in refractive trends and optical components of Hong Kong Chinese aged over 40 years" Ophthalmic Physiol Op 14(4):383-8 (1994)
"Myopia appears to be more prevalent among the younger age groups than the older age groups of the Hong Kong Chinese population, and the importance of genetics in determination of refractive error is called into question by these findings."
Li J, Zhang QJ, Xiao XS, Li JZ, Zhang FS, Li SQ, Li W, Li T, Jia XY, Guo L, Guo XM - "The SNPs analysis of encoding sequence of interacting factor gene in Chinese population" Zhonghua Yi Xue Yi Chuan Xue Za Zh 20(5):454-6 (2003) LINK
- "There was no evidence to prove that mutations in the TGIF gene are responsible for the high myopia in Chinese."
Environmental Factors: Near-Work
Feldkamper M, Schaeffel F - "Interactions of genes and environment in myopia" Dev Ophthalmol 37:34-49 (2003) LINK
- "There is no doubt that an environmental component is involved and extended near work appears to be the major risk factor....A number of systemic or ophthalmic diseases are associated with myopia, indicating that metabolic conditions may interfere either with the gains of the feedback loops or the responses of the target tissue, the sclera."
Fulk GW, Cyert LA - "Can bifocals slow myopia progression?" Am Optom Assoc 67(12):749-54 (1996) LINK
"Myopia progressed more rapidly during the school year than during summer vacation."
Angle J, Wissmann DA - "Age, reading, and myopia" Am J Optom Physiol Opt 55(5):302-8 (1978) LINK
“Regression analysis shows that education explains all the tendency for myopia to appear and progress among 12--17-years-olds.”
Children in urban areas had a higher prevalence and more severe degree of myopia than children in rural areas. (educated vs illiterate). This again disproves the “caused by genetics” hypothesis.
The Framingham Offspring Eye Study Group - "Familial aggregation and prevalence of myopia in the Framingham Offspring Eye Study" Arch Ophthalmol 114(3):326-32 (1996) National Eye Institute, Bethesda, MD, USA.
"...the large increase in myopia prevalence for more recent birth cohorts and the decrease in the strength of the between-siblings association for myopia with increasing between-siblings age difference suggest an important role for environmental factors in the cause of myopia."
Progressive Lenses/Bifocals
Leung JT, Brown B - "Progression of myopia in Hong Kong Chinese schoolchildren is slowed by wearing progressive lenses" Optom Vis Sci. 76(6):346-54 (1999) LINK
"Progressive lenses, which can permit a focused retinal image at distance, intermediate, and near, without accommodation, may slow the development of myopia....Progressive lenses significantly retarded the progression of the myopia in these children."
Fulk GW, Cyert LA, Parker DE - "A randomized trial of the effect of single-vision vs. bifocal lenses on myopia progression in children with esophoria." Optom Vis Sci 77(8):395-401 (2000) LINK
"Use of bifocals, instead of single-vision glasses, by children with near-point esophoria seemed to slow myopia progression to a slight degree."
Fulk GW, Cyert LA, Parker DE - "A randomized clinical trial of bifocal glasses for myopic children with esophoria: results after 54 months" Optometry 73(8):470-6 (2000) LINK
"Wearing bifocals instead of single-vision glasses caused a slowing of myopia progression evident during the first two years. During the subsequent two-and-a-half years of followup, the difference in the degree of myopia was maintained, but did not increase."
Fulk GW, Cyert LA - "Can bifocals slow myopia progression?" Am Optom Assoc 67(12):749-54 (1996) LINK
"Over the whole 18-month study, myopia progressed at rate of 0.57 D/yr for those in single-vision lenses and 0.39 D/yr in those in bifocals (p = 0.26)."
Goss DA, Grosvenor T - “Rates of childhood myopia progression with bifocals as a function of nearpoint phoria: consistency of three studies” Optom Vis Sci 67(8):637-40 (1990) LINK
"Three studies on the effect of bifocal lenses on childhood myopia progression are discussed and re-analyzed. In all three, the rates of progression were less with bifocals than with single-vision lenses in esophoria. Rates with the two types of correction were similar in patients who had nearpoint orthophoria or exophoria."
Negative Lenses - Glasses make it worse...
Saw SM,
Gazzard G, Au Eong KG, Tan DT "Myopia: attempts to arrest progression" Br J
Ophthalmol 86(11):1306-11 (2002)
http://bjo.bmjjournals.com/cgi/content/full/86/11/1306
"Correcting a child’s myopia with negative lenses may result in compensatory aberrant eye growth and the development of myopia".
Angle J, Wissmann DA - "Myopia and corrective lenses" Soc Sci Med [Med Psychol Med Sociol] 14A(6):473-9 (1980)
"Use of negative lenses for the correction of myopia leads to progression."
Sato T - "The Causes and Prevention of Aquired Myopia" Tokyo: Kanehara Shuppon (1957), cited in NAS - Myopia: Prevalence and Progression (1989) LINK
Animal experiments have shown that compensatory changes in the axial length of an eye may occur in response to error signals from lens-induced defocus (Wallman et al, 1995; Hung et al, 1995).
Hung LF, Crawford ML, Smith EL - "Spectacle lenses alter eye growth and the refractive status of young monkeys" Nat Med. 1(8):761-5 (1995) LINK
Wallman J,
Wildsoet C, Xu A, Gottlieb MD, Nickla DL, Marran L, Krebs W, Christensen AM -
"Moving the retina: choroidal modulation of refractive state" Vision Res
35(1):37-50 (1995)
LINK
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Goss DA - "Effect of spectacle correction on the progression of myopia in children--a literature review." J Am Optom Assoc 65(2):117-28. (1994) LINK
- "Methods used to attempt to control childhood myopia progression have included various types of spectacle correction. The most commonly studied technique has been the use of bifocal lenses. METHODS: The literature on the effects of bifocals, undercorrection, and part-time wear of spectacles on the rate of myopia progression in children was reviewed. RESULTS: The data available on undercorrection and part-time wear of spectacles is limited. There have been several studies on the effects of bifocals. Some studies reported no effect with bifocals, some studies reported reduced rates with bifocals, and some noted lower rates with bifocals may be associated with particular ocular or visual findings. CONCLUSIONS: Critical analysis of the literature suggests that when the nearpoint phoria is eso, greater rates of progression occur, and that some degree of myopia control may be established by shifting the phoria into the normal range by spectacle corrections such as bifocals."
Biochemistry: Hormone Implications - Estrogen
Kobayashi K, Mandai M, Suzuma I, Kobayashi H, Okinami S - "Expression of estrogen receptor in the choroidal neovascular membranes in highly myopic eyes" Retina 22(4):418-22 (2002) LINK
- "Estrogen receptor was expressed in the CNVMs in highly myopic eyes, suggesting that estrogen may have important functions in the formation of CNVMs.”
Biochemistry: Transforming Growth Factor (TGF)
Biochemical investigations have revealed that the development of high myopia is associated with altered scleral extracellular matrix biochemistry. Alteration in transforming growth factor (TGF) expression has been shown to be involved in the progression of myopia (Jobling et al, 2004).
"TGF-beta is a protein which acts as a growth inhibitor on various cells such as hepatocytes, vascular endothelial cells, hemocytes, lymphocytes and the like, and locally exists in visual cells (cells responsible for photochemical reaction in the most initial stage of visual reception) in the retina." (Honda et al, 2000)
Recently a US patent has been granted to Honda et al and Senju Pharmaceuticals for concoctions which regulate TGFbeta activation in the treatment of myopia (6,010,699), controlling axial elongation.
TGF has long been known to be a TSH antagonist (Kawaguchi et al, 1997; Delorme et al, 2002). In thyroid cells, TGFbeta1 decreases basal and TSH-stimulated cAMP production and TSH receptor expression (Delorme et al, 2002).
Biochemistry: Dopamine
Stone RA, Lin T, Laties AM, Iuvone PM - "Retinal dopamine and form-deprivation myopia" Proc Natl Acad Sci U S A 86(2):704-6 (1989) FULL TEXT
"Dopamine and its metabolite 3,4-dihydroxyphenylacetic acid are reduced in myopic as compared to control eyes".
Biochemistry: Acetylcholinesterase
Japanese researchers investigating myopia clusters in Japan have found that the reduction of acetylcholinesterase activity coincided with the development of myopia (Ishikawa & Miyata, 1980). There are now many studies available showing the ability of various fluoride compounds in inhibiting acetylcholinesterase. See MEDLINE
Assorted
Zhao J, Mao J, Luo R, Li F, Pokharel GP, Ellwein LB - "Accuracy of noncycloplegic autorefraction in school-age children in China" Optom Vis Sci. 81(1):49-55 (2004) LINK
- "Noncycloplegic autorefraction was found to be highly inaccurate in school-age children and, thus, not suitable for studies of refractive error or for prescription of glasses in this population."
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REFERENCES
Honda S, Watanabe N, Ogawa T - "Method for controlling axial length of the eye" US Patent 6,010,699 (2000)
Ishikawa S ,Miyata M - "Development Of Myopia Following Chronic Organophosphate Pesticide Intoxication: An Epidemiological And Experimental Study" Neurotoxicity of the Visual System, Merigan, W. H., and B. Weiss, Editors; Raven Press, New York, pages 233-254 (1980)
The reduction of acetylcholinesterase activity coincided with the development of myopia...
Jobling A, Nguyen M, Gentle A, McBrien NA - "Isoform-specific changes in scleral TGF-beta expression and the regulation of collagen synthesis during myopia progression" J Biol Chem. 2004 FULL TEXT
Kawaguchi A,
Ikeda M, Endo T, Kogai T, Miyazaki A, Onaya T - "Transforming growth
factor-beta1 suppresses thyrotropin-induced Na+/I- symporter messenger RNA and
protein levels in FRTL-5 rat thyroid cells" Thyroid 7(5):789-94 (1997)
Lam CS, Edwards M, Millodot M, Goh WS - "A 2-year longitudinal study of myopia progression and optical component changes among Hong Kong schoolchildren" Optom Vis Sci. 76(6):370-80 (1999) LINK
Lin LL, Shih YF, Hsiao CK, Chen CJ, Lee LA, Hung PT - "Epidemiologic study of the prevalence and severity of myopia among schoolchildren in Taiwan in 2000" J Formos Med Assoc 100(10):684-91 (2000) LINK
Miroshnychenko A - Sosnivka FINAL REPORT, USAID SCIENTIFIC ASSESSMENT GRANT # 1210003-0-00 8086-00 (2000)
Quek TP, Chua CG, Chong CS, Chong JH, Hey HW, Lee J, Lim YF, Saw SM - "Prevalence of refractive errors in teenage high school students in Singapore" Ophthalmic Physiol Opt 24(1):47-55 (2004) LINK
Raja Reddy
D, Deme SR - "Skeletal Fluorosis" (2000)
http://210.210.19.130/vmu1.2/dmr/dmrdata/cme/fluorosis /Fluorosis.htm
Raja Reddy D
- Skeletal fluorosis, in: Handbook of neurology. Eds.Vinken,P.J. and Bruyn,G.W.
North Holland Publishing Co. Amsterdam, 465-504 (1978)
Raja Reddy D - "Some observations on fluoride toxicity" Nimhans J 3 (1985)
Sperduto RD, Seigel D, Roberts J, Rowland M - "Prevalence of myopia in the United States" Arch Ophthalmol 101(3):405-7 (1983) LINK
Tay MT, Au Eong KG, Ng CY, Lim MK - "Myopia and educational attainment in 421,116 young Singaporean males" Ann Acad Med Singapore 21(6):785-91 (1992) LINK
Villarreal GM, Ohlsson J, Cavazos H, Abrahamsson M, Mohamed JH - "Prevalence of myopia among 12- to 13-year-old schoolchildren in northern Mexico" Optom Vis Sci 80(5): 369-73 (2003)
Ueda K - "Agricultural chemical poisoning" Naika 27(3): 530-2 (1971)
A clustering of cases of myopia among school children in Nagano Prefecture and in Osaka was noted in the 1970s and considered to be due to organophosphate poisoning.
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