Epidemiology of Refractive Errors
An interplay among corneal power, lens power, anterior chamber depth, and axial length determines an individual’s refractive status. All 4 elements change continuously as the eye grows. On average, babies are born with about 3.00 D of hyperopia. In the first few months of life, this hyperopia may increase slightly, but it then declines to an average of about 1.00 D of hyperopia by the end of the first year because of marked changes in corneal and lenticular powers, as well as axial length growth. By the end of the second year, the anterior segment attains adult proportions; however, the curvatures of the refracting surfaces continue to change measurably. One study found that average corneal power decreased 0.10–0.20 D and lens power decreased about 1.80 D between ages 3 years and 14 years.
From birth to age 6 years, the axial length of the eye grows by approximately 5 mm; thus, one might expect a high prevalence of myopia in children. However, most children’s eyes are actually emmetropic, with only a 2% incidence of myopia at 6 years. This phenomenon is due to a still-undetermined mechanism called emmetropization. During this period of eye growth, a compensatory loss of 4.00 D of corneal power and 2.00 D of lens power keeps most eyes close to emmetropia.
Figure 3-14 shows the distribution of refractive errors in a large population based study. Figure 3-15 shows the effects of age on the prevalence of refractive errors.
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Prevent Blindness America; National Eye Institute. Vision Problems in the U.S.: Prevalence of Adult Vision Impairment and Age-Related Eye Disease in America. Available at www.visionproblemsus.org. Accessed October 4, 2017.
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Wolfram C, Höhn R, Kottler U, Wild P, Blettner M, Bühren J, Pfeiffer N, Mirshahi A. Prevalence of refractive errors in the European adult population: the Gutenberg Health Study (GHS). Br J Ophthalmol. 2014;98(7):857–61.
Excerpted from BCSC 2020-2021 series : Section 3 - Clinical Optics. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.