WHAT IS MYOPIA?
What Is Myopia?
Myopia is a progressive visual disorder that results in poor distance vision. If the myopia is severe, it will impair near vision as well. Myopia is also known as "near-sighted" or "short-sighted." In addition to weakening vision, it also changes the physical structure of the eye. It can steepen the front surface of the eye (cornea) and/or stretch the retina (axial elongation). These changes increase the risk of future eye disease (see The Dangers of Myopia). It is one of the leading causes of blindness around the world and has a direct association with retinal detachments and glaucoma.
Myopia definitely has a genetic link. However it is driven more by the environmental stress of near work such as reading, studying, computer use, hand games and the lack of outdoor time. In fact, one theory of increasing myopia is that it is our eye’s method of adapting to the demand of prolonged near work. It takes less work for a myopic person to read. That's why we call it "near-sighted". Humans before the Industrial Revolution used their eyes predominantly for distance seeing. During that period, the incidence of myopia was less than five percent. In a recent study, researchers found that myopia has increased 66 percent in the United States from 1971 to 2004 (See Health Issues: The Myopia Epidemic).
The Dangers Of Myopia
Myopia and its progressive disorders can cause abnormal or adverse ocular changes. High myopia may cause thinning and weakening of the retina (the thin membrane at the back of the eye that contains the rods and cones). Abnormal stretching or elongation of the eye may pull on the vitreous (the gel substance that fills the eye) which in turn pulls on the retina leading to its detachment. A detached retina can lead to blindness. This elongating process can also cause "lattice-like" holes to occur in the peripheral retina. These holes can allow fluid to seep under the retina-- lifting and detaching it. Again, possibly leading to a permanent loss of sight.
Moderate to high myopic people are twice as likely to develop glaucoma. (Mitchell 2000). Further, the detection of myopia is much more difficult due to the deforming of the optic nerve head as a result of ocular elongation. The optic nerve head is one of the structures closely examined for changes due to glaucoma. It is difficult to determine if the changes are due to myopic stretching or glaucoma
Health Issues: The Myopia Epidemic
- The World Health Organization (WHO) projects 2.5 billion nearsighted people by year 2020. Approximately 80% of elementary students in Singapore are myopic.
- 90% of college students in China are nearsighted.
- The National Institutes of Health reports that in 1972, the frequency of myopia was 25% in U.S. individuals aged 12 to 54. By 2004, it had increased to 41.6%. (Roan,2010).
- In 2004 approximately 26% of all people living in the U.S. and Europe were myopic.
- The incidence of myopia in "hunter-gatherer" societies where children perform little near work, is about 1%.
Myopia Development: Research
■ Working at near distances can result in the development of myopia
- Introduction of school systems in cultures in which they did not previously exist has resulted in greater incidence of myopia (Young et al., 1970).
- Occupations dealing with intense near point activity lead to further myopic development (Adams and McBrien 1992).
- Cross sectioned studies have found associations between near work and myopia progression ( Saw et al., 1996; Saw et al 1999).
- Study of 153 Singaporean children determined higher progression rates for younger children and those with higher amounts of myopia at the beginning of the study (Saw et al. 2000).
- Children are especially susceptible to near work causing myopia (Goss, 1994).
- Young adults ages 20-30 years have developed late onset of myopia that has coincided with beginning intense near work and in many cases, using a computer ( Sheedy, Shaw-McMinn, 2003).
■ Myopia Development and Convergence Excess (Esophoria*)
- Esophoria is a risk factor in myopia development In children (Chung, 2009).
- Esphoria results in larger accommodative lag, resulting in retinal blur (Goss and Rainey,1990)
- Esophoria is a condition where the eyes tend to turn inward excessively when doing near tasks
■ Myopia Development and Heridity
- The Orinda Longitudinal Study of Myopia (Zadnik, 1997). Children become emmetropic as the eye's axial length increases and the crystalline lens decreases in power. Parental history of myopia is the predominant factor for myopic development which is not due to myopic parents having an effect on near work activity.
■ Myopia Development and Computers
- Tokoro (1988) reports myopic progression after 1 year of work on computers. Toppel and Neuber (Thomson,2002) studied refractive error change over 2 years as opposed to control group.
- Mutti and Zadnik ( 1996) No compelling evidence that computers are any more significant then reading in progressive myopia.
- University of California at Berkley (UCBSO Study,2002) – premature myopia may result in children five to twelve years of age doing computer work for more than two hours a day.
- Yeow & Taylor demonstrated a transient myopia is common effect of accommodative stress at the computer screen. The authors also documented a myopia shift of .12D in a group of computer users as compared to a control group. Transient myopia changes have been shown objectively to result from temporary changes in accommodation (Zheng,Yan et al,2008).
■ Myopia Development and Accommodation
- (Comet Study, 2003) To prove or disprove the theory that children with poor accommodative response may find progressive lenses beneficial for slowing the progression of myopia. The Comet Study was a randomized clinical trial designed to test the effectiveness of plus lenses against the progression of myopia in children. Progressive addition lenses (PALs), also called "no-line bifocals" were used in the experimental group. After three years, the study found practically no difference between the group that wore the PALs versus the ones that wore standard lenses for myopia.
■ Myopia Developmentand Corneal Reshaping (Orthokeratology)
- The studies that address myopic progression and Ortho-K are Reim, LORIC, CRAYON, SMART, MCOS and CRIMP.
- REIM (2003). Tom Reim OD,FOAA and colleagues first reported the potential of myopia control in 2003 with a retrospective study that reported that corneal reshaping experienced about a sixty percent reduction in myopic progression.
- LORIC (2005). The Longitudinal Orthokeratology Research in Children(LORIC) study was conducted in Asia, and found a much slower rate of myopia and axial elongation(47%) among young progressive myopes who underwent corneal reshaping compared to those who wore eyeglasses.
- CRAYON (2007). The Corneal Reshaping and Yearly Observation of nearsightedness(CRAYON) study, conducted by Jeff Walline OD,FAAO at Ohio State University, also found lower rates of myopia progression and axial elongation(57%)(Walline, 2008).
- SMART in progress. Both the LORIC and CRAYON studies were small in scale involving fewer then forty patients. The Stabilization of Myopia by Accelerated Reshaping Technique(SMART) study, a large scale(300 patient),five year longitudinal, multicenter evaluation of the effectiveness of corneal reshaping for young progressive myopes is now underway. First year results are encouraging (Eiden et al,2009).
- CRIMP(2010) . Corneal reshaping inhibits myopia progression(CRIMP) is a ten year retrospective study out of Australia that demonstrated control of myopia progression over a ten year time frame. Fully 70% of all participants in the corneal reshaping control group did not progress in degree of myopia over the period studied.
- MCOS in progress. " The Myopia Control with Orthokeratology contact lenses in Spain (MCOS) Study, in which continued documentation of safety outcomes for corneal reshaping in a pediatric population was evident by no changes in best-corrected visual acuity or significant adverse health effects from ortho-k wear" (Gregory,2010).
Myopic Development-Thoughts: Nature vs Nurture
The Adolescent Myope- Excessive near point among adolescents may lead to nearsightedness at an early age
A genetic adaptation for survival may unwittingly lead to early childhood myopia when the eyes instead of being used for distance viewing are involved in excessive close work focusing. This genetic adaptation is called emmetropization. The word emmetropization means that the eye is going to the state of emmetropia, i.e. to a state where proper focusing of distant objects can be achieved with a relaxed focusing of the eyes. Emmetropization is also used to describe the ability of the eye to adjust the eye growth in length during development for optimal optical imaging. Emmetropization in the sense of an adjustment of the length of the eye to achieve proper vision when meeting the needs of an individual, who would mostly use their vision for distance viewing, is necessary when considering the individually different optical parameters of the eye before emmetropization takes place. Emmetropization has to be seen as a very smart mechanism to balance for inborn optical differences and deficiencies. In the history of human development both definitions matched, because mostly the dominating viewing distance was the far distance. Today, with often excessive near work, both definitions of emmetropia are controversial: If the eye adjusts to the dominating viewing distance it will often become not emmetropic, but myopic!
Ancestry and Myopia - nature
Is there a racial affinity towards myopia? In China, a 5% incidence of myopia entering elementary school becomes 25% in 5th grade and 90% incidence of myopia among college students. Among Japanese, Korean and Jewish children myopia incidence has increased dramatically over the last half century. Are these changes due purely to genetics or are there cultural, dietary or other environmental causes?
The Child with Two Myopic Parents - nature
This is the strongest single factor in predicting myopia for an offspring. Is there a Myopia Gene? Is there a set of special characteristics like esophoria ( eye over crossing at close work), elongated eyes or steeper than normal corneas that are passed on through the genetics?
The Computer User With Recent Onset Of Myopia- nurture
Eyes are poorly equipped to deal with extended hours in front of a computer screen . What is Computer Vision Syndrome (CVS)? It is a multifaceted combination of eye and vision problems related to near work experienced during or following computer use. CVS affects up to 75% of computer users to some degree and 10 million eye doctor visits last year reported the primary complaint was eyestrain coming from computer use. This was not existent in 1970. While there is no direct correlation between time spent on a computer and myopia the successful student is often nearsighted.
The Child Athlete- Spatial Awareness Factor - nuture
Studies point to spatial awareness as a significant positive factor in avoiding progressive myopia. Possible reasons maybe children playing at sports are not in front of computers or reading during that activity. It is also postulated that balance and agility gained from sports may be significant development that works against myopia.
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