Journal of Refractive Surgery

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Prevalence of Myopia in Adults: Implications for Refractive Surgeons

Catherine A McCarty, PhD, MPH; Patricia M Livingston, PhD; Hugh R Taylor, MD, FRACO, FRACS

Abstract

ABSTRACT

BACKGROUND: We reviewed the research on the prevalence of myopia in the adult population to compare the refractive distribution of patients being treated with excimer laser photorefractive keratectomy to correct myopia, and assess the potential market for excimer laser surgery.

METHODS: All published reports of myopia prevalence in adults were reviewed, as well as the prevalence in the Melbourne "Visual Impairment Project and the distribution of refractive errors treated by the Melbourne Excimer Laser Group in 1994.

RESULTS: A large population-based study of people aged 4 to 74 years in the U.S. showed that 43% had low myopia (less than -5.00 diopters (D)), 3.2% had high myopia (-5.01 to -10.00 D), and 0.2% had extreme myopia (more than -10.00 D). In Asian populations these proportions may be much higher and in African and Pacific island groups, much lower. In the Melbourne Visual Impairment Project, we found the prevalence of low myopia was 21%, high myopia 2%, and extreme myopia 0.3%. A single excimer laser has operated for 3 years in Melbourne. Of those treated, 45% had low myopia, 42% high myopia, and 13% extreme myopia. Compared to low myopes, high myopes were ten times (OR: 9.8; Confidence interval: 6.69 to 12.91) more likely to have excimer laser treatment and extreme myopes were 16 times (OR: 16.40; Confidence interval: 12.53 to 20.27) more likely.

CONCLUSIONS: Although there are many more people with lower amounts of myopia in the population and the clinical results have been more predictable after one procedure in this group, the perceived benefits of excimer laser treatment may be greater for those with higher amounts of myopia, thus influencing their decision to undergo excimer laser surgery to correct their myopia. There is clearly a large market potential for excimer laser surgery in people with low myopia. [J Refract Surg 1997;13:229-234]

Abstract

ABSTRACT

BACKGROUND: We reviewed the research on the prevalence of myopia in the adult population to compare the refractive distribution of patients being treated with excimer laser photorefractive keratectomy to correct myopia, and assess the potential market for excimer laser surgery.

METHODS: All published reports of myopia prevalence in adults were reviewed, as well as the prevalence in the Melbourne "Visual Impairment Project and the distribution of refractive errors treated by the Melbourne Excimer Laser Group in 1994.

RESULTS: A large population-based study of people aged 4 to 74 years in the U.S. showed that 43% had low myopia (less than -5.00 diopters (D)), 3.2% had high myopia (-5.01 to -10.00 D), and 0.2% had extreme myopia (more than -10.00 D). In Asian populations these proportions may be much higher and in African and Pacific island groups, much lower. In the Melbourne Visual Impairment Project, we found the prevalence of low myopia was 21%, high myopia 2%, and extreme myopia 0.3%. A single excimer laser has operated for 3 years in Melbourne. Of those treated, 45% had low myopia, 42% high myopia, and 13% extreme myopia. Compared to low myopes, high myopes were ten times (OR: 9.8; Confidence interval: 6.69 to 12.91) more likely to have excimer laser treatment and extreme myopes were 16 times (OR: 16.40; Confidence interval: 12.53 to 20.27) more likely.

CONCLUSIONS: Although there are many more people with lower amounts of myopia in the population and the clinical results have been more predictable after one procedure in this group, the perceived benefits of excimer laser treatment may be greater for those with higher amounts of myopia, thus influencing their decision to undergo excimer laser surgery to correct their myopia. There is clearly a large market potential for excimer laser surgery in people with low myopia. [J Refract Surg 1997;13:229-234]

The prevalence and causes of myopia have been the topic of many investigations in the last quarter century, as evidenced by 1666 citations from the National Library of Medicine, (Bethesda, Maryland) in article titles since 1966. A number of researchers have demonstrated an increase in the prevalence of myopia in the population over a relatively short period of time1"2, fueling the debate about the relative contributions of heredity versus environment to rates of myopia in the population.

In the absence of effective primary prevention techniques to control an increase in the prevalence and incidence of myopia, refractive surgeons have the potential to improve the distance vision of many people through refractive keratotomy, excimer laser photorefractive keratectomy (PRK), or photoastigmatic refractive keratectomy (PARK). Photorefractive keratectomy and photoastigmatic refractive keratectomy have been shown to be reliable for the correction of low amounts of myopia.3"9

Effective estimation of market size and planning of service delivery requires knowledge of the distribution of myopia in a given population in comparison with the population currently accessing excimer laser services. It has been estimated that the break even point for one operating excimer laser in a 1-million person population is 500 cases per year, assuming a 1% penetration rate (GK Kliman, paper presented at the 1994 Annual Meeting of the American Academy of Ophthalmology, San Francisco, California). Epidemiologic information about myopia would clearly be useful to refractive surgeons for strategic planning and marketing.

Table

Table 1Review of Literature on the Prevalence of Myopia in the Asia Pacific Region

Table 1

Review of Literature on the Prevalence of Myopia in the Asia Pacific Region

We reviewed the research on the prevalence of myopia, to compare the refractive distribution of patients currently being treated with the excimer laser for correction of myopia, to assess the potential market for excimer laser surgery, and to consider epidemiologic factors which may influence the use of excimer laser surgery in the population.

REVIEW OF PUBLISHED PREVALENCE DATA

Although there has been extensive research about risk factors for the development and progression of myopia, there is a paucity of population-based research on the prevalence or incidence of myopia. Papers were selected for review by employing the search words "myopia" and "epidemiology" or "prevalence" in a search of the entire Medline database. The bibliographies of relevant articles were then reviewed to obtain other articles pertaining to the prevalence of myopia that were published prior to 1966, the first year that articles are available on Medline. Articles were included if they contained data on spherical equivalent in adults. Articles related exclusively to refractive errors in children were excluded, as were articles that did not present spherical equivalent data. Studies of myopia progression, myopia in graduate students, law students or other specific subgroups, and non-English language studies were not included in this review.

Unless mentioned, the following definitions of myopia were employed: low myopia, -5.00 D or less (spherical equivalent); high myopia, -5.01 to -10.00 D; extreme myopia, more than -10.00 D.

Data on the prevalence of myopia in the Asia Pacific region are scarce (Table 1). The few data that were available indicate that populations closer to native traditional living may experience less myopia than more developed populations.1113 For example, in Polynesia a 1% prevalence of myopia in children living in Vanuatu (aged 6-17 years)14 and a 4% prevalence of myopia among school-children on Tobago Island15 form a striking contrast to Asian populations which may experience more myopia.11 This situation was highlighted by Lin et al16, who found a prevalence of myopia in Taiwan of approximately 90% in high schools.16"19 While there is recognition of the potentially immense market for refractive surgery in the Asian community, one must be cautious when reviewing these results because the final outcome of refraction after the period of growth, ie, after puberty, can be very different. Although changes in the development of the eye are usually completed by the age of 14, small changes can still occur until the age of 20. Epidemiologic studies have shown that axial length and refraction do not stabilize until after puberty. It is preferable to assess the prevalence of myopia in the adult population to demonstrate the potential market for refractive surgery.

Table

Table 2Review of Literature on the Prevalence of Myopia in North America

Table 2

Review of Literature on the Prevalence of Myopia in North America

Data on the prevalence of myopia from population-based epidemiologic studies in other areas of the world are rare (Tables 2 and 3). They generally support anecdotal evidence that myopia is rare in less developed populations. The degree and distribution of refractive errors, however, varies widely, from 2% low myopia in Eskimos aged 4017 to 55.5% low myopia in females of all ages in Ontario.19 In studies of North American Eskimos eonducted in 1973,17 198523 and 199 124, a dramatic increase in the prevalence of myopia has been observed. Although some of the difference could be attributed to different Eskimo populations, changes in measurement, or some other detection bias, these studies provide convincing evidence that the prevalence of myopia in Eskimo populations may be increasing. Increases in myopia prevalence has also been noted in Danish2 and Icelandic30 populations. Although more data from well conducted epidemiologic studies are needed, it is clear that the potential market for surgical correction of myopia is great worldwide, and may be increasing.

Melbourne Visual Impairment Project

The Melbourne Visual Impairment Project was a population-based study of the distribution and determinants of eye disease in Melbourne residents aged 40 years or more from nine randomly selected Melbourne suburbs. The detailed methodology has been reported elsewhere.35 In brief, nine pairs of adjacent census collector districts were randomly selected from the Melbourne Statistical Division. A door-to-door household census was taken to identify all eligible persons- those aged 40 years or more in the calendar year of examination and who had lived at that address for 6 months or more. Information about household characteristics and basic demographic data were collected during a brief interview conducted at the household. Eligible individuals were then invited to a local examination site for an eye examination and personal interview. The examination included measurement of visual acuity, visual fields, a detailed interview on the person's medical history, smoking, alcohol, and vitamin usage, dietary intake, history of sunlight exposure, clinical examination, and fundus and lens photography. As part of the examination, uncorrected and spectacle-corrected visual acuity were assessed on a 4 meter LogMAR chart. Refraction was checked on a Humphrey autorefractor and current lens prescription was assessed with the Humphrey Lens Analyser.

Data were available for 3262 participants, representing an 83% participation rate (Table 4). In this study population, the prevalence of myopia was 23.7%. The proportion of participants with myopia was similar in males and females when controlling for age (xp 2 = 2.26; p = 0.13) and decreased significantly with age when controlling for gender (xp 2 = 5.98; p = 0.01). The distribution of amount of myopia was similar in the entire cohort, after excluding people with cataract(s). These data suggest an increase in the prevalence and degree of myopia in Australia, as the prevalence of low myopia in Australian Europeans in the early 1970s was 5.9%12 compared to 21% in the Melbourne Visual Impairment Project cohort.

Table

Table 3Review of Literature on the Prevalence of Myopia in Africa, Central America, Europe, Greenland, Iceland, India, and Israel

Table 3

Review of Literature on the Prevalence of Myopia in Africa, Central America, Europe, Greenland, Iceland, India, and Israel

Further analysis indicated that 51% of people less than 60 years of age with annual incomes over $41,000 were more likely to be dissatisfied with their distance vision (unpublished data). This would suggest a large potential market for excimer laser surgery. Comparisons between the Melbourne Visual Impairment Project sample and the Beaver Dam Eye Survey36 in the United States highlighted similar levels of myopia (right eye only, Melbourne Visual Impairment Project: 22.4% vs Beaver Dam Eye Survey: 26.2%; xp 2 = 0 .43; p = 0.51). However, the decline in prevalence with age was not as significant in the Melbourne Visual Impairment Project as in the Beaver Dam Survey with 24% of the Melbourne Visual Impairment Project sample 75 to 84 years of age affected by myopia compared with 14% in the Beaver Dam Eye Survey (Table 5).

Melbourne Excimer Laser Group

The Melbourne Excimer Laser Group has been performing photorefractive and photoastigmatic keratectomy since November 1991.9 Patients are eligible for surgery if they are at least 21 years of age, give informed consent, have stable myopia, have spectacle-corrected visual acuity of 20/60 in both eyes, have stable keratometry after discontinuing soft contact lens wear for 1 week or hard contact lens wear for 1 month, and are available to attend follow-up examinations for at least 1 year. Exclusion criteria include a history of keratoconus, ocular surgery or trauma, or therapy likely to interfere with corneal healing. These inclusion and exclusion criteria are based on clinical and epidemiologic data. The 21-year age criterion is related to the stable myopia criterion, in that epidemiologic studies have shown that axial length and refraction do not stabilize until after puberty.

Table

Table 4Distribution of Refractive Errors in the Melbourne Visual Impairment ProjectTable 5Prevalence of Myopia in the Right Eye, by Age, in the Melbourne Visual Impairment Project and Beaver Dam Eye Survey

Table 4

Distribution of Refractive Errors in the Melbourne Visual Impairment Project

Table 5

Prevalence of Myopia in the Right Eye, by Age, in the Melbourne Visual Impairment Project and Beaver Dam Eye Survey

For all initial refractive treatments, the distribution of preoperative spherical equivalent at the spherical plane in 1994 were: 143 eyes (45%) low myopia, 134 eyes (42%) high myopia, and 43 eyes (13%) extreme myopia. Considering the distribution of refractive errors from the Melbourne Visual Impairment Project, there was an overrepresentation in the high and extreme myopes of the population that elected to undergo excimer laser correction of their myopia. Applying these figures to the myopia prevalence figures from the Melbourne Visual Impairment Project, high myopes were ten times more likely (OR: 9.8; Confidence interval: 6.69 to 12.91) to undergo excimer laser surgery as low myopes, and extreme myopes were 16 times more likely (OR: 16.40; Confidence Interval: 12.53 to 20.27) to undergo excimer laser surgery compared with low myopes.

DISCUSSION

There is clearly a large potential market for refractive surgery in the world. The U.S. market is estimated to be anywhere from 9 to 57 million and could lead to increased revenue of $1 to 8.5 billion to ophthalmologists, depending on market penetration (L. Haimovitch, paper presented at the 1994 Annual Meeting of the American Academy of Ophthalmology, San Francisco, California). As we have shown, high and extreme myopes in Melbourne are more likely to undergo excimer laser surgery than low myopes. Moreover, people less than 60 years of age with higher incomes are more likely to be dissatisfied with their distance vision. This highlights the potential market in the population for excimer laser surgery.

With the Melbourne Visual Impairment Project age restriction of at least 40 years of age, there are limitations in extrapolating results from the Melbourne population-based sample to the excimer laser population. Although population-based information on the prevalence of myopia across all age groups is not available, it is likely that myopia is becoming more prevalent and that the relative distribution of refractive error is similar across age groups, but shifted toward myopia in the younger age groups. The ratio from one group to the next should remain constant, and we therefore believe this comparison does provide insight on the kind of patients who present for refractive surgery. This is of additional interest because several studies have demonstrated less reliable results from excimer laser surgery in high and extreme myopia.3741

Consumer fears and negative publicity about poor outcomes of excimer laser surgery could limit the market for refractive surgery. In terms of marketing potential, low myopes clearly represent an enormous untapped market. Refractive surgeons need to be aware of the epidemiologic data related to myopia prevalence in addition to information about outcomes of surgery and employ these data in their strategic marketing of refractive procedures.

REFERENCES

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18. Boniuk V. Refractive problems in native peoples. Can J Ophthalmol 1973;8:229-233.

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Table 1

Review of Literature on the Prevalence of Myopia in the Asia Pacific Region

Table 2

Review of Literature on the Prevalence of Myopia in North America

Table 3

Review of Literature on the Prevalence of Myopia in Africa, Central America, Europe, Greenland, Iceland, India, and Israel

Table 4

Distribution of Refractive Errors in the Melbourne Visual Impairment Project

Table 5

Prevalence of Myopia in the Right Eye, by Age, in the Melbourne Visual Impairment Project and Beaver Dam Eye Survey

10.3928/1081-597X-19970501-08

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