Individuals with high myopia had a significantly increased lifetime risk of more serious visual impairment according to risk estimates extrapolated from data of more than 15,000 participants, researchers reported.
Based on projections of the association between axial length, spherical equivalent, and visual impairment as a function of age, visual impairment will increase 7- to 13-fold by 2055 in areas with high rates of myopia, according to Caroline Klaver, MD, PhD, Erasmus Medical Center, Rotterdam, the Netherlands, and colleagues.
The prevalence of visual impairment rose with increasing axial length and spherical equivalent, so that among participants with high myopia, cumulative risk of visual impairment was 5.7% at 60 years and 39% at 75 years. Cumulative incidence of visual impairment was 3.8% for participants age 75 years with an axial length of 24 to less than 26 mm, and greater than 90% with an axial length of 30 mm or greater, they wrote in JAMA Ophthalmology.
"Our projections show that, given increasing axial lengths, myopia will bring major threats to the visual health of the public in many societies. Given the global increase of myopia and rise in high myopia, strategies to prevent and overcome visually impairing complications must be developed. This requires increased awareness among policy makers and medical experts regarding myopia-related risks," the authors stated.
Nearsightedness is becoming the most common eye disorder to cause blindness in younger adults in many parts of the world due to complications such asmyopic macular degeneration, early cataract, retinal detachment, and/or glaucoma, the authors explained.
The worldwide prevalence of myopia and high myopia has already been projected to increase two-fold (from 22%) and five-fold (from 2%), respectively, from 2000 to 2050, they stated, and developing strategies to prevent the myopia and its complications could help to avoid an increase of visual impairment in the working-age population.
The data on spherical equivalent and axial length of the right eye were gathered from several population-based studies and a case-control study in the Netherlands, conducted during four 2- or 3-year periods beginning in 1990 and ending in 2012. Analyses were then extrapolated to published reports on populations with increasing prevalence of high myopia from Singapore and Republic of Korea.
Participants were categorized as younger than 60 years or 60 years or older for analyses, which were adjusted for sex, age, and cohort. Mean age was 61.3 , and 57% of participants were female. Axial length ranged from 15.3 to 37.8 mm; 819 individuals had an axial length of 26 mm or greater. Spherical equivalent ranged from −25 to +14 diopters, while 796 persons had high myopia, or a spherical equivalent of −6 diopters or less, with an axial length generally exceeding 26 mm.
The authors' estimation that patients with high myopia have about a one in 2.6 lifetime chance of developing visual impairment may be conservative, given that life expectancy often exceeds 75 years, wrote Jacqueline Chua, PhD, and Tien Yin Wong MBBS, PhD, of the Singapore Eye Research Institute, in an accompanying editorial.
That the risk of visual impairment increased with increasing axial length is important, in that using traditional refractive error cutoffs of −6.00 or −8.00 D7 to define pathological myopia may not identify all individuals at risk and may in fact be misleading to patients, they wrote.
"The association of axial length with refractive error is 0.75 (P<0.001), so not all patients with longer axial length will have greater degrees of myopia and vice versa," they noted.
The observation that even simple myopia carries a lifetime risk of visual impairment strengthens support for attempts to prevent simple myopia, whether by environmental measures (outdoor activities) or by pharmacological interventions, they stated. While randomized clinical trials indicate that low-dose atropine eye drops may help prevent myopia progression in children, accurate risk estimation of visual impairment and cost-benefit analysis are needed, they added.
Study limitations included selective nonparticipation of disabled persons in the population-based studies, and selective participation of visually disabled persons in one cohort; possible overestimation of cumulative risk in the extremely high myopia group due to the relatively low number of participants at higher ages; and the projection of data from a European study population to Asian ethnicities.
Chua and Wong pointed out that the study lacked information on specific causes of visual impairment. "The public should be more educated about the potential risks of myopia, and patients with high myopia should be more aware of new symptoms or deteriorating vision and should not hesitate to seek an ophthalmic assessment," the editorialists wrote. "Ophthalmologists should be aware of the potentially blinding complications of myopia, including the latest research and treatment options. In turn, optometrists should not regard their options for managing myopia to be restricted to prescribing spectacles or contact lens."