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Reading in Close-up Settings Will Damage Your Vision –
A Myopic Understanding?
October 24, 2008
Have you ever been told that reading in the dark or holding a book too closely to your face will make you go blind, hurt your eye-sight, or so on? This contemporary claim is one of many infamously instilled in children by their peers and mentors, be it a concerned parent or friend, but what is the biophysical rationale behind the eye degenerating from use in close-up or low-light settings? How common is this claim, and what does the scientific evidence say about the validity of this idea? This paper will seek to look deeper into the claim and see what science has revealed so far about this issue.
Close-up Low-Light Vision, Eye Strain, and Eventual Nearsightedness
The common claim being investigated here is that working visually with objects close to one’s face (such as with reading regardless of the level of brightness) will strain one’s eyes and eventually lead to permanent eye damage, specifically nearsightedness or myopia. However, what process occurs in the eye that is attributed to this long term damage?
The following is a biophysical explanation of the short term health problems associated with reading in low-light settings followed by an explanation for the damage caused by long-term, low-light visual behavior. According to HowStuffWorks.com:
“When you read, your eye must be able to focus an image of the words onto your retina. To do this, the iris, as well as the muscles that control the shape of your lens, must contract to keep the focused image on the retina. If you read in low light, your visual muscles get mixed signals: Relax to collect the most light, but at the same time, contract to maintain the focused image. When that object is poorly lit, focusing becomes even more difficult because the contrast between the words and the page is not as great, which decreases the eye's ability to distinguish visual detail. … Your eyes have to work harder to separate the words from the page, which strains your eye muscles. Consider this to be strenuous exercise for your eye muscles. So your eye muscles will ache, much as your arm muscles and leg muscles become sore after strenuous exercise. When your eyes are working this hard for a long period of time, the strain may cause a number of physical effects. Symptoms of eye strain include sore eyeballs, headaches, back and neck aches, drooping eyelids and blurred vision. Because you often don't blink enough when focusing on a single object, you may also experience uncomfortable dryness in your eyes. None of this damages your eyes, and all of it eventually goes away after you stop straining them.” (http://www.howstuffworks.com/question462.htm)
The issue of long term eye damage is discussed by Science NetLinks.com here:
“[T]here's a chance that you will become more nearsighted if you read in low light … because in low light, your pupil has to open up wider to let in enough light to see. That changes where light normally hits the retina, blurring the image. So the eye gets a signal to grow longer, so the image will hit the right place on the retina. And that can eventually cause nearsightedness. … The larger the pupil, the greater the blur, and the greater the blur, the stronger the signal is for the eye to grow longer, and hence, become more nearsighted. … [D]amage is more likely to occur in young people, where eyes are still developing.” (http://www.sciencenetlinks.com/sci_update.cfm?DocID=85)
From what is stated above, the short term affects of low-light visual activity can be seen, and a proposed reason for long term damage to the eyes from such activity is given. Furthermore, the same basis for low-light visual impairments comes from long term, up-close visual activity as well; Long term strain on the eyes as well as varying levels of light under which people read accounts for similar eye damage as with low-light settings. For the purpose of this paper, no distinction is made between reading in low-light settings and long-term, up-close visual action.
Now that the basis for how the eye can possibly be damaged under these settings has been made, an analysis of various online sources, such as medical, university, or popular online question databases, and the advice they offer shall be made, followed by a comparison to a number of scientific studies that have been conducted on the matter.
Claims and Popular Perspective
Many online sources, such as AboutCures.net, DocShop.com, and the Cleveland Clinic, have done their own independent inquiry into the matter and/or offer the advice that no long-term harm comes from low-light reading, implicitly or explicitly saying that myopic eyesight develops on a genetic basis (http://aboutcures.net/2008/02/25/mythbust-monday-will-reading-in-the-dark-damage-your-eyes/) (http://www.docshop.com/2007/12/04/most-common-eye-myths-exposed-the-focused-truth/) (http://my.clevelandclinic.org/healthy_living/eye_care/hic_your_eyes_separating_fact_from_fiction.aspx). The basis for these claims is the scientific evidence that heredity factors control for the presence of myopia, not personal behavior.
And there are others, such as a Cornell University representative on Science NetLinks.com and an scientific study from the British Medical Journal reported on by BBC News, that state the exact opposite – that state that reading and related behaviors can lead to nearsightedness, with the BMJ article giving further rationale behind what factors do and don’t apply here (http://www.sciencenetlinks.com/sci_update.cfm?DocID=85) (http://news.bbc.co.uk/1/hi/health/1993012.stm). These studies point to research done that finds common factors between myopic people, indicating that a non-genetic basis for the development of myopia exists.
However, some sources, such as HowItWorks.com and the University of Illinois Eye & Ear Infirmary, make the claim that there is no concern for long-term damage to the eye in low-light settings while still noting that there is continuing debate among scientists and medical professionals about the potential for nearsightedness based on environmental behavior – that of close-range, low-light, visual activities (http://www.howstuffworks.com/question462.htm) (http://www.agingeye.net/visionbasics/visionmyths.php). The Eye Digest from the University of Illinois discusses how the scientific debate today has become an issue of nature versus nuture, and it specifically states that:
“While "myopes tend to beget myopes" heredity is not destiny and other factors are at work in determining refractive state of the eye. For centuries, the correlation of near work and myopia has been characterised by vision researchers. Epidemiological surveys have shown that myopia is more prevalent in individuals who spend more time reading or performing close work than those who spend more time not using their eyes at near. Myopia has been correlated with the amount of school work and level of educational attainment (Br J Ophthalmol. 2001;85:509-10). The process continues into the third decade of life with graduate students, microscopists, and military conscripts becoming more myopic with more near work. Showing correlation of near work and enviornmental influences (reading in dark) with myopia is relatively simple and there are many anecdotal studies (as well as numerous personal experience stories) testifying to such a correlation. Proving causation is much more difficult. To better understand and study the effect of visual environment on the developing eye, research in animal models is underway. Overall it seems enviornmental factors do play a role - how much? - we do not know as of yet.” (http://www.agingeye.net/visionbasics/visionmyths.php)
The final type of articles found online, such as in the New York Times and New York University’s Scienceline, have much to do with the above paragraph as stated by The Eye Digest of the University of Illinois; they acknowledge the short-term eye problems caused by close, low-light visual activity and point to studies that indicate a heredity basis for myopia as commonly attributed to reading in the dark, but they also point out a number of epidemiological studies that indicate behavioral factors having some degree of impact (http://www.nytimes.com/2006/07/04/health/04real.html) (http://scienceline.org/2007/10/03/ask-peck-darkeyesmyopia/). Studies like these and others will be looked at below as this paper transitions from what popular opinions say to what has been found in various scientific studies on this issue.
Before moving, however, it seems appropriate to note that there is equal consideration of both rationale for myopia from health related, news, scientific, and popular internet sources, so it seems that there does not appear to be any overtly biased representation of one reason over the other, just that there simply seems to be a dualistic scientific explanation for myopia, but the question of the day is are they mutual exclusive or not? Can long term strain on the eye be negligible on myopia development, or does genetics and behavior play a combined role?
What the Scientific Evidence Says
To being with an overview of a number of scientific studies, this section will begin by looking solely at the studies that have tried to isolate as many desired variables as possible within a given population in order to determine which target variables could be contributing to the occurrence or development of myopia in a population. For the following studies, non-biological characteristics were examined.
The first study examined involved a population study in western Newfoundland. Ocular refraction (for a measure of nearsightedness), work at close range or nearwork (hours per day), and education (years) were measured for 957 persons comprising 80% of the population aged 5 years and above of three different communities. The findings of this study were that refraction was moderately, consistently and significantly correlated with nearwork from ages 5 to 60, and remained so after adjustments for the association of refraction and nearwork levels in relation to age, sex and education. Multiple regression coefficients relating refraction to nearwork decreased from -0.43 D/h at ages 5-14 years to -0.22 D/h at ages 60 years and up. The magnitude of this association, and its consistency and persistence over a wide age range, suggest that large amounts of nearwork in childhood may contribute to the prevalence of clinical myopia (Richer & Bear, 1980, pp. 469-478). In light of the original question, it seems that this study indicates there is a non-biological basis for myopia, and that nearwork seems to have a larger correlation to myopia during adolescent life than at later life. Note, however, that these are only explorations of correlations, not causations.
Another study to be looked at is one that involves 1204 Chinese school children aged 10 to 12 years from three different schools. After controlling for age, gender, school, parental myopia, father's education, and books read per week, myopia of at least -0.5 D was associated with high nonverbal IQ (highest quartile) versus low IQ (lowest quartile) (odds ratio = 2.4; 95% confidence interval, 1.7-3.4). Controlling for the same factors, children with higher nonverbal IQ scores had significantly more myopic refractions (-1.86 D for children with nonverbal IQ in the highest quartile compared with -1.24 D for children with nonverbal IQ in the lowest quartile; P = 0.002) and longer axial lengths (24.06 mm versus 23.80 mm; P = 0.022). Nonverbal IQ accounted for a greater proportion of the variance in refraction compared with books read per week. The conclusion of this study was that nonverbal IQ may be an independent risk factor of myopia, and this relationship may not be explained merely by increased reading (books per week) among myopes. An interesting observation is that nonverbal IQ may be a stronger risk factor for myopia when compared with books read per week. The complexity of the relationships between nonverbal IQ, reading, and myopia warrant additional studies to clarify any cause-effect relationship (Saw et al., 2004). Here, a rather unusual suspect is found for an epidemiological basis for myopia. Let’s examine another.
In a study in Singapore, computerized data of 110,236 males aged 15 to 25 (mean 17.75) years who underwent compulsory medical examination from April 1987 to January 1992 were used to estimate the prevalence and severity of myopia among young Chinese, Malay, Indian and Eurasian Singaporean males with different educational levels. The prevalence and severity of myopia amongst the groups with different educational levels were compared and were fairly well-matched for important known confounding factors such as age, sex, race and degree of urbanization of place of residence. This data showed a positive association between educational attainment and both the prevalence and severity of myopia. Both the prevalence of myopia and the proportion of myopes with severe myopia were in general higher among those with more years of formal education (Eong, Tay, & Lim, 1993). An important point to note here is that education level was the main factor analyzed, not the amount of time spent with nearwork. Also, notice that these studies aren’t searching for genetic mechanisms but rather epidemiological sources for myopia that lead to a closer examination of factors that cause myopia.
A number of studies are seen above that to link behavior and situations with the development of myopia, but the following study indicates a hereditary or biological mechanism for the development of myopia. How could this be?
One hereditary study from the Journal of the American Medical Association evaluated whether eye size and shape was different in children based on their parental history of myopia. The study involved a community-based cohort study of school children aged 6 to 14 on four campuses of the Orinda Union School District, a predominantly white, high socioeconomic status community in a cross-sectional volunteer sample of 716 children (662 non-myopic) in the first, third, and sixth grades in 1989, 1990, and 1991. The four measures taken for the experiment were refractive error (measured by autorefraction), corneal curvature (measured by photokeratoscopy), crystalline lens power (measured by video phakometry), and axial ocular dimensions (measured by ultrasonography), and the study came to the conclusion that with prevalent cases of myopia excluded and grade in school and "near work" controlled for, children with two myopic parents had longer eyes and less hyperopic refractive error (analysis of covariance, P < or = .01) than children with only one myopic parent or no myopic parents as well as the observation that a model incorporating parental history is only improved by the addition of near work for the prediction of refractive error. This means that even before the onset of juvenile myopia, children of myopic parents have longer eyes, suggesting that the premyopic eye in children with a family history of myopia already resembles the elongated eye present in myopia.
(Zadnik, Satariano, Mutti, Sholtz, & Adams, 1994).
Based on these studies’ possibly conflicting results on the cause of myopia, looking at studies that involve analysis of both hereditary and environmental factors seems to be the next most logical course of action, and a study in the Investigative Ophthalmology and Visual Science journal from 2002 does just that, but before examining it, let us look at one more study that clearly outlines non-hereditary influences on myopia:
“Many people have reduced unaided vision because of myopia, a spherical error of refraction. The biological theory of myopia views myopia as the result of genetically determined characteristics of eye tissues, whereas the use-abuse theory views myopia as the result of habitual use of the eye at a near focal length, near-work. The use-abuse theory implies that myopia is prevent able whereas the biological theory does not. Myopia varies over age, gender, race, ethnicity, level of education, social class and degree of urbanization. The explanation of the epidemiology of myopia in the use-abuse theory is that some types of people do more near-work than others. Using data from the Health Examination Survey of 12 to 17-year-olds conducted by the US Public Health Service from 1966–1970, this paper finds that the use-abuse theory can explain at least some of the variance of myopia and much of the socially patterned variance. This finding raises the possibility that at least some of the myopia extant in a population is preventable (Angle & Wissmann, 1980, pp. 220-228).”
The differences between the varying groups can be seen in a table from the study below:
As can be seen, there is definitely evidence of environmental factors being correlated to myopia as well as heredity. A study from Investigative Ophthalmology and Visual Science that wanted to quantify the degree of association between juvenile myopia and parental myopia, near work, and school achievement compared all of these factors together and found that among 366 eighth graders who participated in this longitudinal study, heredity was the most important factor associated with juvenile myopia, with smaller independent contributions from more near work, higher school achievement, and less time in sports activity. It also found that there was no evidence that children inherit a myopigenic environment or a susceptibility to the effects of near work from their parents (Mutti, Mitchell, Moeschberger, Jones, & Zadnik, 2002). What does this study that incorporates the individual explanations from the other studies reveal?
Summary and Conclusion
When measured independently, it appears heredity does play a large role in determining the development of myopia from childhood, but it also appears that other biological or behavioral influences can help contribute to myopia’s development, such as IQ, close visual work/dimly-lit settings, level of education, sex, and so on. With all these things and others playing a role, only the final study examined here can give a comparison between them all to determine which plays a greater role in the development of myopia, and this study determined that heredity by far was the greatest role in determining myopia development, with the other behavioral influences also contributing in part the development of myopia although to a lesser degree. To narrow down the exact causes of myopia, more studies will need to be done like this last one to determine what preventable, environmental factors can be more strongly associated with myopia’s development, and appropriate preventative efforts can proceed from there. Also, if a multivariate study could be done that compares the differences between long-term eye use (such as is found in levels of education and hours spent reading), light levels for long-term visual use (a potentially confounding variable), and eye strain reducing techniques that are practiced in the long-term (which could further provide insight into heredity versus behavior arguments concerning myopia), then much more insight could be given into this issue.
For now, and to be the safest until a more conclusive and all-encompassing opinion has been reached on the matter within the medical community, it probably doesn’t hurt to take the advice found on HowStuffWorks.com:
“If you are comfortable reading with a flashlight (or other low light) and don't experience any of the above symptoms of eye strain, it's probably fine for you to read this way. It's certainly easier on your eyes to read in good light, however. You can also avoid eye strain when you're reading by blinking frequently and taking a moment to focus on something out the window or across the room every 15 to 30 minutes. (http://www.howstuffworks.com/question462.htm)”
Richler A, Bear JC. Refraction, nearwork and education. A population study in Newfoundland. (1980). [Electronic version] Acta ophthalmologica, 58(3), 498-78. Retrieved October 7, 2008, from PubMed database.
Saw SM, Tan SB, Fung D, Chia KS, Koh D, Tan DT, Stone RA. IQ and the Association with Myopia in Children. (2004). [Electronic version] Investigative Ophthalmology and Visual Science, 45, 2943-2984. Retrieved October 7, 2008, from PubMed database.
Au Eong KG, Tay TH, Lim MK. Education and myopia in 110,236 young Singaporean males. (1993). [Electronic version] Singapore Medical Journal, 34(6), 489-492. Retrieved October 7, 2008, from PubMed database.
K. Zadnik, W. A. Satariano, D. O. Mutti, R. I. Sholtz and A. J. Adams. The effect of parental history of myopia on children's eye size. (1994). [Electronic version] JAMA, 17, 271. Retrieved October 8, 2008, from JAMA database.
J. Angle and D. Wismann. The Epidemiology of Myopia. (1980). [Electronic version] American Journal of Epidemiology, 111(2), 220-228. Retrieved October 8, 2008, from PubMed database.
Donald O. Mutti, G. Lynn Mitchell, Melvin L. Moeschberger, Lisa A. Jones and Karla Zadnik. Parental Myopia, Near Work, School Achievement, and Children's Refractive Error. (2002). [Electronic version] Investigative Ophthalmology and Visual Science, 43, 3633-3640. Retrieved October 9, 2008, from PubMed database.
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