Objective To report the percentage of new cases of myopia in 4927 children aged 5 to 16 years who participated in the Collaborative Longitudinal Evaluation of Ethnicity and Refractive Error Study between 1989 and 2009.
Design A multicenter, longitudinal, observational, volunteer study of refractive error and ocular development in children from 5 racial/ethnic groups in which the participants were children who were not myopic (right eye cycloplegic autorefraction of less myopia/more hyperopia than −0.75 diopters [D] in both principal meridians) at study entry. A new case was a diagnosis of myopia (right eye cycloplegic autorefraction of −0.75 D or more myopia in both principal meridians) after study entry.
Results Of the 4556 children entering the study who were not myopic, 749 (16.4%) received a diagnosis of myopia after study entry. Among these 749 children, the ages of the participants at diagnosis varied from 7 to 16 years, with the largest number diagnosed at age 11 years (136 participants [18.2%]). New cases of myopia occurred in 27.3% of Asians, 21.4% of Hispanics, 14.5% of Native Americans, 13.9% of African Americans, and 11% of whites. Female participants had more new cases than did male participants (18.5% vs 14.5%). Normal-birth-weight children had more new cases than did low-birth-weight children (16.9% vs 15.5%).
Conclusions Sixteen percent of children enrolled in the Collaborative Longitudinal Evaluation of Ethnicity and Refractive Error Study developed myopia during their school-aged years. The percentage increased yearly until age 11 years, after which it decreased. New cases of myopia varied by ethnic/racial group.
Myopia is a common and serious problem because of its high prevalence, ocular morbidity, and cost of treatment. Myopia commonly occurs in children during their early school years and increases in magnitude as they get older. Only a small number of studies1-5 have reported the number of new cases of myopia that develop in children during their primary school years.
The studies reporting new cases of myopia have been limited to children of 1 or 3 ethnic/racial groups,1-5 have emphasized Asian children,2-5 have been performed outside of the United States,1-5 have had no follow-up period1 or short follow-up periods3-5 of 1 to 3 years, have had small sample sizes,1,2,5 and/or have not used cycloplegia for refractive error measurement.2 The Collaborative Longitudinal Evaluation of Ethnicity and Refractive Error (CLEERE) Study is a longitudinal study with a design that addresses many of the limitations of these other studies. The CLEERE Study was conducted in the United States and included 4927 children from 5 ethnic/racial groups: Asians, African Americans, Hispanics, Native Americans, and whites. The study included children from grades 1 through 8 (ages 5-16 years) and tested them each year. Each ethnic/racial group included 500 or more children. The purpose of this research is to report the percentage of new cases of myopia in the CLEERE Study from children who were not myopic when they entered the study.
During the period from 1989 to 2009, a total of 4927 children 5 to 16 years of age participated in the CLEERE Study, an observational study of ocular component development and risk factors for the onset of myopia in children of various ethnicities. The CLEERE Study is an extension of the Orinda Longitudinal Study of Myopia, begun in 1989 in the predominantly white community of Orinda, California. To improve generalizability, 4 additional clinic sites were added in 1997 to recruit African American children (Eutaw, Alabama), Asian children (Irvine, California), and Hispanic children (Houston, Texas). Testing of Native American children began in Tucson, Arizona, in 2001. Each affiliated university's institutional review board (University of California, Berkeley; The Ohio State University; University of Alabama at Birmingham; Southern California College of Optometry; University of Houston; and University of Arizona) approved informed consent documents according to the tenets of the Declaration of Helsinki. Parents provided consent and children assent before the children were examined.
Ethnic/racial group designation was determined from a medical history form that had been completed by a parent. Parents selected 1 of the following 6 ethnic/racial designations (corresponding to the categories used by the National Institutes of Health as of 1997 when these data were first gathered): American Indian or Alaskan Native; Asian or Pacific Islander; black or African American not of Hispanic origin; Hispanic; white not of Hispanic origin; and other or unknown. Ethnicity was assigned to the target ethnic group for the given site when parents provided more than 1 ethnic/racial designation that included the site's targeted group (1.7% of subjects). If parents provided more than 1 ethnic/racial designation and neither included the site's targeted designation, the child was assigned to the nonwhite ethnic/racial designation. Any missing parent-reported data were filled in from investigator observation (5.7% of subjects). Investigator observation showed excellent agreement with parent-reported ethnic/racial designation. As children completed grade 8, they left the study and were replaced with newly enrolled first graders for a period of 3 years at the University of Alabama at Birmingham School of Optometry and the University of Houston College of Optometry, for 5 years at the Southern California College of Optometry, and for 8 years at the University of California, Berkeley, School of Optometry. At the Department of Ophthalmology and Vision Science at the University of Arizona, children were enrolled from 2001 to 2004 and were followed up until grade 8. Because of student transfers to other schools, study withdrawal for other reasons, and termination of the study at a site before all of its participants reached eighth grade, not all children had complete follow-up through eighth grade. A total of 61.1% of the sample was at least 13 years old at the last study visit.
Trained and certified examiners measured central refractive error using the Canon R-1 autorefractor (which is no longer manufactured) between 1989 and 2000 and using the Grand Seiko WR 5100-K autorefractor between 2001 and 2007. Participants were tested after mydriasis and cycloplegia. When a participant had an iris color of grade 1 or 2, testing was done 30 minutes after 1 drop of proparacaine hydrochloride, 0.5%, and 2 drops of tropicamide, 1%.6 When a participant had an iris color darker than grade 2, testing was done 30 minutes after 1 drop of proparacaine, 0.5%, and 1 drop each of tropicamide, 1%, and cyclopentolate hydrochloride, 1%.6
Myopia was defined as −0.75 diopters (D) or more myopia in both principal meridians. The results also include myopia defined as −0.50 D or more myopic spherical equivalent refraction to facilitate the comparison of these results with other studies. Low birth weight was defined as less than 2500 g. Four other definitions of myopia are used in Tables 1 and 2 (−0.75 D and −1.00 D spherical equivalent, −0.50 D or more myopia, and −1.00 D or more myopia in both principal meridians) to describe the effect of myopia definition on the number of participants without myopia entering the study and the number of new cases of myopia.
The CLEERE Study data set includes 4927 children. The range of myopia prevalence at study entry was from 12.9% to 8.5% for a spherical equivalent of −0.50 D and −1.00 D or more myopia in both principal meridians, respectively (Table 1). From the total sample, there were 4556 children who were not myopic when they entered the study.
During the course of the CLEERE Study, the percentage of children becoming myopic using the definition of −0.75 D or more myopia in both principal meridians was 16.4%; using the definition of −0.50 D spherical equivalent or more myopia, the percentage of children becoming myopic was 23.4%. Not surprisingly, the number of new cases of myopia was sensitive to myopia definition, with spherical equivalent–based definitions yielding more cases of myopia than definitions based on the refractive error in both principal meridians. Using the most restrictive definition of myopia, −1.00 D or more myopia in both meridians, we categorized 14% of the children as having become myopic (Table 2).
The age at onset of myopia ranged from 7 to 16 years. The highest percentage of new cases of myopia, 18.2%, occurred at age 11 years using the CLEERE Study definition of −0.75 D or more myopia in both meridians and at age 10 years using the spherical equivalent of −0.50 D or more myopia definition. The largest percentage increase in new cases occurred between ages 7 and 9 years. After ages 10 to 11 years, there was a steady decrease in the percentage of new cases of myopia (Table 3).
The percentage of new cases of myopia varied among the 5 different ethnic/racial groups. Asians had the largest percentage of new cases, and whites had the smallest percentage. The percentages of new cases using the CLEERE Study definition of −0.75 D or more myopia in both principal meridians were 27.3% in Asian children, 21.4% in Hispanic children, 14.5% in Native American children, 13.9% in African American children, and 11% in white children. The ranking of the ethnic/racial groups from highest to lowest in the percentage of new cases was essentially the same for both the CLEERE Study definitions of −0.75 D and −0.50 D spherical equivalent cut points, except for a reversal between African American and Native American rankings using the −0.50 D spherical equivalent definition (Table 4).
Table 4 also shows the children's ages at study entry and at study exit and their years of follow-up in the CLEERE Study. For the more conservative definition of myopia (ie, −0.75 D or more myopia in both meridians on cycloplegic autorefraction), the range in mean age at study entry for those who entered the CLEERE Study as participants without myopia was about 1 year, lowest for whites (8.11 years) and highest for Native Americans (9.45 years). The range in mean age at study exit was 2 years, lowest for Asians (11.60 years) and highest for Native Americans (13.46 years). The mean number of years of follow-up ranged from 3.44 years for Asians to 4.30 years for whites.
Overall, 18% of the sample of participants who entered the CLEERE Study in the first grade as participants without myopia and developed myopia by the eighth grade were followed up all the way through to grade 8. Table 5 shows the myopia onset results for the children whose last visit was conducted when they were at least 13 years old. In summary, there were 649 of 2536 children or 25.6% new cases of myopia by the spherical equivalent of −0.50 D or more myopia definition among those last seen at age 13 years or older compared with the 1006 of 4290 children or 23.4% new cases of myopia shown in Table 2 for the same myopia definition. The corresponding comparison for the myopia definition of −0.75 D or more myopia in both meridians is 494 of 2734 children 13 years of age or older (18.1%) vs 16.4% in Table 2. The inclusion of children of all ages, regardless of the years of follow-up or their age at last study visit, underestimates the proportion of new cases of myopia by about 2%.
There was a small difference in the onset of new cases of myopia by sex that was consistent across both the −0.75 D CLEERE Study definition of myopia and the −0.50 D spherical equivalent definition of myopia. Using the CLEERE Study definition of −0.75 D or more myopia in both meridians, we found that 18.5% of female participants and 14.5% of male participants were new cases of myopia. (Table 6).
Low birth weight has been associated with the onset of myopia.7 Among the children in the CLEERE Study, there was a clinically inconsequential 1.4% difference between the normal-birth-weight and low-birth-weight groups. The percentage of new cases of myopia with normal birth weight was 16.9%, and the percentage of new cases of myopia with low birth weight was 15.5%.
Studying the development of myopia in children is difficult. As a result, few large studies have been conducted that assessed new cases of myopia in children.1-5 Factors that make studying myopia development difficult include the gradual onset of the condition, the relatively few new cases that occur each year, the need to follow up with the same children for many years, and the difficulty in obtaining access to children. Because of these problems, a large initial group of children who can be followed up for many years is required. This study design is expensive and requires a long-term commitment by a group of investigators, their institutions, and the parents who provide access to their children.
To our knowledge, there are no other studies that have the combined characteristics of the CLEERE Study (ie, a large number of children, a long duration of follow-up, and a diverse ethnic/racial mix of children). The small number of existing myopia development studies were generally well done but were limited in different ways. Zhao et al,3 Fan et al,4 and Saw et al5 only followed up with their initially nonmyopic children for 1 to 3 years. Edwards2 followed up with children for 5 years but did not use cycloplegic autorefraction to measure myopia and only had 110 nonmyopic children. Most of the studies were limited to Asian children in the Far East,2-5 usually Chinese children from different areas, except for one study by Mäntyjärvi1 that enrolled Finnish children from 1 community. Two studies that had large sample sizes of 3149 (Fan et al4) and 4621 (Zhao et al3) only followed up with children for 1 and 2 years, respectively.
The percentage of new cases of myopia is dependent on the definition of myopia. The CLEERE Study definition, −0.75 D or more myopia measured by cycloplegic autorefraction in both principal meridians, was chosen because this amount of myopia is likely to affect school and other daily activities, such as seeing the board from the back of a classroom, viewing television across a room, and playing sports. It was also chosen because it exceeded the measurement error of autorefraction8 and because it appeared to be the minimum amount that most clinicians would prescribe for a newly myopic child. The −0.50 D or more myopia spherical equivalent definition used in earlier studies is more liberal and could include some refractive errors that are not traditionally defined as myopia (eg, mixed astigmatism). Because the spherical equivalent definition includes lower amounts of myopia and refractive errors that are not traditionally defined as myopia, the percentage of new cases with this definition was, of course, greater than the percentage of new cases using the definition in the CLEERE Study. This is an important factor to recognize when groups with high astigmatism are included and spherical equivalent is a less useful definition.
Myopia is a problem that affects children of all ages, both sexes, and many ethnic/racial groups. In the CLEERE Study, at least 1 of 6 children had myopia (−0.75 D or more myopia in both principal meridians on cycloplegic refraction) by the age of 16 years. Although there were differences in the percentage of new cases of myopia between different ethnic/racial groups, every group had at least 11% of children who became myopic.
The 3 largest existing studies3-5 of myopia development reported new cases of myopia, using a definition of −0.50 D or more myopia spherical equivalent that occurred after 1 to 3 years of follow-up in mostly Chinese children. Fan et al4 reported that 14.4% of their sample of children became myopic after 1 year of follow-up and that 10-year-old boys and 11-year-old girls had the highest amounts of myopia. Zhao et al3 reported that 18.5% of children (cumulative incidence) became myopic after a 28.5-month follow-up period: children 5 years of age had the smallest amount of myopia, children 12 years of age had the largest amount, and girls had more myopia than did boys. Saw et al5 reported that 42.7% of children (cumulative incidence) became myopic over a 3-year follow-up period, 49.5% among 737 Chinese children and 27.2% among 229 Malaysian and 53 Indian children.
These results are difficult to compare with the CLEERE Study because the CLEERE Study included different ethnic/racial groups and the Asians in the CLEERE Study were not limited to Chinese children; however, the Asian children in the CLEERE Study and the Chinese children in the previous 3 studies3-5 had significant amounts of myopia, using the −0.50 D or more myopia spherical equivalent definition. The results of the CLEERE Study and these 3 studies3-5 agree that the number of new cases of myopia appears to peak at ages 10 to 12 years.
This study was intentionally designed so that each site preferentially recruited the ethnic/racial group that was best represented in its surrounding community. For example, all the Asian children were recruited in California; of course, expecting recruitment of Asian children in either Eutaw, Alabama, or Houston, Texas, would have been in vain. It is difficult, therefore, to separate out the effects of location and socioeconomic status from ethnicity/race, and it is also difficult to envision a study design in which these 3 variables could be separated from one another. Nonetheless, the necessity of site-specific and ethnicity/race-specific recruitment is a limitation of the CLEERE Study.
The CLEERE Study shows that myopia was present in a small percentage of children aged 7 years. More children became myopic every following year as the children continued in school through age 16 years. More than 75% of the new cases of myopia occurred in children between the ages of 9 and 13 years. This onset and development pattern was the same regardless of the definition of myopia.
There was a small difference in the percentage of new cases of myopia between the sexes, with girls having more new cases compared with boys. This result is similar to the results found in other studies.1,3-5 This result could possibly occur because girls mature earlier than boys, and this result would be consistent with the trend of an increasing number of new cases of myopia with increasing age.
This study found a small difference in the percentage of new cases of myopia in children who had a normal birth weight compared with those with a low birth weight. The percentage was higher in children with normal birth weight, which would not support possible associations between low birth weight and myopia. Further studies may be needed to determine whether there is a difference in myopia between infants with low birth weight only and those with low birth weight and other risk factors or diseases, such as Down syndrome or retinopathy of prematurity.
The CLEERE Study sample is not representative of the population of children in the United States. Studies in the United States9,10 that attempted to be representative of the entire population and collected vision data did not assess the development of myopia in school-aged children. Although the CLEERE Study is not representative, it is, to date, the largest and most diverse longitudinal study of refractive error in children in the United States. With an awareness of this limitation, one can cautiously use the data to make limited inferences about the development of myopia in children. Trends in the CLEERE Study sample include the observation of a slow rate of onset of myopia in young children, with the highest percentage of new cases of myopia around the presumed age of puberty; the effect of myopia definition on the number of new cases; the relative equality in the number of new cases of myopia between girls and boys; and, within ethnic/racial groups, the highest percentage of new cases of myopia among Asians compared with other groups.
With the continual onset of new cases of myopia during the primary school years, there needs to be a means of identifying children who become myopic so that they receive treatment. Unfortunately, the Patient Protection and Affordable Care Act signed into law on March 23, 2010, may not include vision care for children, unless they are eligible for Medicaid. Because of this general lack of vision care for children, additional work will be needed to ensure that all myopic children receive the treatment they need.
One in 6 children enrolled in the CLEERE Study became myopic. These included children from each major ethnic/racial group: Asians, African Americans, Hispanics, Native Americans, and whites. Among those becoming myopic, the age at onset peaked at around the ages of 10 to 11 years. There was no clinically significant difference in new cases of myopia between the normal-birth-weight and low-birth-weight groups. The high percentage of new cases of myopia in the CLEERE Study sample is consistent with the findings of others and supports the need for new programs and policies to address myopia in children.
Members of the CLEERE Study (as of March 2012)
The CLEERE Study Group Clinical Centers
Franklin Primary Health Center, Inc, Eutaw, AL: Sandral Hullett, MD, MPH (principal investigator, 1997-2006); Robert N. Kleinstein, OD, MPH, PhD (coinvestigator, 1997-2006); Janene Sims, OD (optometrist, 1997-2001 and 2004-2006); Raphael Weeks, OD (optometrist, 1999-2006); Sandra Williams (study coordinator, 1999-2006); LeeAndra Calvin (study coordinator, 1997-1999); Melvin D. Shipp, OD, MPH, DrPH (coinvestigator, 1997-2004).
University of California, Berkeley School of Optometry: Nina E. Friedman, OD, MS (principal investigator, 1999-2001); Pamela Qualley, MA (study coordinator, 1997-2001); Donald O. Mutti, OD, PhD (principal investigator, 1996-1999); Karla Zadnik, OD, PhD (optometrist, 1996-2001).
University of Houston College of Optometry, TX: Ruth E. Manny, OD, PhD (principal investigator, 1997-2006); Suzanne M. Wickum, OD (optometrist, 1999-2006); Ailene Kim, OD (optometrist, 2003-2006); Bronwen Mathis, OD (optometrist, 2002-2006); Mamie Batres (study coordinator, 2004-2006); Sally Henry (study coordinator, 1997-1998); Janice M. Wensveen, OD, PhD (optometrist, 1997-2001); Connie J. Crossnoe, OD (optometrist, 1997-2003); Stephanie L. Tom, OD (optometrist, 1999-2002); Jennifer A. McLeod (study coordinator, 1998-2004); Julio C. Quiralte (study coordinator, 1998-2005).
Southern California College of Optometry, Fullerton: Susan A. Cotter, OD, MS (principal investigator, 2004-2006; optometrist, 1997-2004); Julie A. Yu, OD (principal investigator, 1997-2004; optometrist, 2005-2006); Raymond J. Chu, OD (optometrist, 2001-2006); Carmen N. Barnhardt, OD, MS (optometrist, 2004-2006); Jessica Chang, OD (optometrist, 2005-2006); Kristine Huang, OD (optometrist, 2005-2006); Rebecca Bridgeford (study coordinator, 2005-2006); Connie Chu, OD (optometrist, 2004-2005); Soonsi Kwon, OD (optometrist, 1998-2004); Gen Lee (study coordinator, 1999-2003); John Lee, OD (optometrist, 2000-2003); Robert J. Lee, OD (optometrist, 1997-2001); Raymond Maeda, OD (optometrist, 1999-2003); Rachael Emerson (study coordinator, 1997-1999); Tracy Leonhardt (study coordinator, 2003-2004).
University of Arizona, Department of Ophthalmology and Vision Science, Tucson: J. Daniel Twelker, OD, PhD (principal investigator, 2000-2010); Dawn Messer, OD, MPH (optometrist, 2000-2010); Denise Flores (study coordinator, 2000-2007); Rita Bhakta, OD (optometrist, 2000-2004); Katie Garvey, OD (optometrist, 2005-2008); Amanda Mendez Roberts, OD (optometrist, 2008-2010).
Chairman's Office, The Ohio State University College of Optometry, Columbus: Karla Zadnik, OD, PhD (chairman, 1997-present); Jodi M. Malone Thatcher, RN (study coordinator, 1997-2011).
Videophakometry Reading Center, The Ohio State University College of Optometry, Columbus: Donald O. Mutti, OD, PhD (director, 1997-present); Huan Sheng, MD, PhD (reader, 2000-2006); Holly Omlor (reader, 2003-2006); Meliha Rahmani, MPH (reader, 2004-2007); Jaclyn Brickman (reader, 2002-2003); Amy Wang (reader, 2002-2003); Philip Arner (reader, 2002-2004); Samuel Taylor (reader, 2002-2003); Myhanh T. Nguyen, OD, MS (reader, 1998-2001); Terry W. Walker, OD, MS (reader, 1997-2001); Vidhya Subramanian, MS (reader, 2006-2007).
Optometry Coordinating Center, The Ohio State University College of Optometry, Columbus: Lisa A. Jones-Jordan, PhD (director, 1997-present); Linda Barrett (data entry operator, 1997-2007); John Hayes, PhD (biostatistician, 2001-2007); G. Lynn Mitchell, MAS (biostatistician, 1998-present); Melvin L. Moeschberger, PhD (consultant, 1997-present); Loraine T. Sinnott, PhD (biostatistician, 2005-present); Pamela Wessel (program coordinator, 2000-present); Julie N. Swartzendruber, MA (program coordinator, 1998-2000).
Project Office, National Eye Institute, Rockville, MD: Donald F. Everett, MA.
Karla Zadnik, OD, PhD (chairman); Lisa A. Jones, PhD; Robert N. Kleinstein, OD, MPH, PhD; Ruth E. Manny, OD, PhD; Donald O. Mutti, OD, PhD; J. Daniel Twelker, OD, PhD; Susan A. Cotter, OD, MS.
Correspondence: Karla Zadnik, OD, PhD, College of Optometry, The Ohio State University, 338 W 10th Ave, Columbus, OH 43210 (firstname.lastname@example.org).
Submitted for Publication: November 28, 2011; final revision received March 21, 2012; accepted March 28, 2012.
Published Online: June 11, 2012. doi:10.1001 /archophthalmol.2012.1449
Author Contributions: Drs Sinnott, Jones-Jordan, and Zadnik had full access to all the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.
Financial Disclosure: None reported.
Funding/Support: This work was supported by National Eye Institute/National Institutes of Health grant U10-EY08893, the Lions Eye Research Foundation, and the E. F. Wildermuth Foundation. The CLEERE Study was also supported by the National Eye Institute/National Institutes of Health grant U10-EY08893 and by the Ohio Lions Eye Research Foundation and the E. F. Wildermuth Foundation.
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