BARCELONA — In light of the increasing prevalence of myopia in certain parts of the world, ophthalmologists should advise parents on ways to curb the development of myopia in children and intervene early if myopia is progressing rapidly, experts said here at the 17th EURETINA Congress.
The prevention of myopia is important because of the correlation between myopia and high myopia, said Andrzej Grzybowski, MD, PhD, from the University of Warmia and Mazury in Olsztyn, Poland.
"Historically, people believed that low myopia never becomes high myopia," he explained. "However, we know now that high myopia might be a continuation of low myopia."
In about 10% of people, myopia progresses in severity. High myopia, in turn, increases the risk for cataract, glaucoma, and retina disorders. "When you have neovascularization in high myopia, more than 90% of people lose their vision," said Dr Grzybowski.
"There is no doubt that there is an epidemic of myopia in certain parts of the world," said Ian Morgan, PhD, from the Australian National University in Canberra.
In developed countries in East and Southeast Asia with intensive education systems, such as China, Taiwan, and South Korea, the prevalence of myopia has surged since the 1960s. According to the latest estimates, 80% to 90% of students in these countries who complete secondary school are myopic, and 20% are highly myopic, defined as a spherical equivalent refractive error of more than –6 diopters, Dr Morgan reported.
The two major risk factors are educational pressures and the limitation of outdoor time, he said. Unlike students in Western countries, Chinese students typically spend the whole school day indoors.
The same pattern is found within ethnic populations. For example, boys in religious schools in Israel — who must meet higher educational standards than girls — have myopia rates similar to those of Chinese students. However, among other Israelis, including girls in the same schools, the prevalence is lower.
In populations in which European descent is dominant, the overall data on prevalence are conflicting, Dr Morgan said.
In studies of adolescents and young adults that rely on cycloplegia, which are considered to be most accurate, the prevalence of myopia is 20% to 30% in Australia, Northern Ireland, and Poland. By contrast, in studies of adults that do not use cycloplegia, the prevalence of myopia is 40% to 50% in the United States and about 30% in the United Kingdom.
The prevalence of myopia is not as high in Western countries as it is in Asia, but that will likely increase as the pressure for educational attainment increases and as children spend more leisure time with electronic devices, said Dr Morgan.
The risk for progression from myopia to high myopia appears to be greater in Asian than in white people, said Akito Hirakata, MD, from the Kyorin University School of Medicine in Tokyo, who addressed maculopathy during the session.
The precise effect of genetic and environmental factors on progression remains to be determined, Dr Hirakata told Medscape Medical News.
High myopia generally occurs in people older than 50 years, so the wave of high myopia seen in Asian countries might not have hit Western countries yet, he added.
The complications "could be very difficult to treat, especially retinal detachment, so we're a little bit nervous," he explained.
The exact cause of myopia is unclear, but exposure to light and time spent focusing at a distance both play a role, Dr Grzybowski told Medscape Medical News.
Light triggers the production of dopamine and melatonin, which help regulate development of the eyes, he noted.
The way light focuses on the retina also affects this regulation. "Children who read from less than 30 centimeters are more likely to develop myopia," he said. "The longer the reading distance, the better." For that reason, he recommends that children read with ample lighting.
Beyond encouraging outdoor activities, ophthalmologists should suggest intervention to the parents of children whose myopia is progressing by 1 diopter or more per year, said Dr Grzybowski.
Evidence shows that the progression of myopia can be slowed with atropine, soft contact lenses with myopia control features, or orthokeratology, he reported.
Research so far has shown that atropine has the clearest effect on myopia. Concentrations from 0.01% to 1.0% have been effective in slowing myopia by about 50%, but higher doses are associated with adverse reactions, such as photophobia, decreased visual acuity, and abnormalities of accommodation, he pointed out.
"Atropine must be given for 2 years, sometimes longer," Dr Grzybowski said. However, because it can decrease progression by 50%, "a child could end up at 5 diopters instead of 10 diopters."
The effects of pirenzepine, orthokeratology, and peripheral defocus-modifying contact lenses have been shown to be moderate but statistically significant, he reported, adding that pirenzepine is not commercially available.
In contrast, the effect of rigid gas-permeable contact lenses, soft contact lenses, undercorrected single-vision spectacle lenses, and timolol have not been shown to be statistically significant, he said.
But results from preliminary studies of 7-methylxanthine, a nonselective adenosine antagonist, have been promising, he pointed out.
All available treatments come with drawbacks, Dr Grzybowski explained. Children can have difficulty managing contact lenses, and their use carries the risk for corneal damage and infection.
"From my perspective, atropine is easier," he said, but he acknowledged that the long-term effects of the drug are not well known. In addition, because atropine is not manufactured for ophthalmic use, the quality varies from one compounding pharmacy to another, and little information is available on the stability of the preparations that any of them prepare, he said.
These problems show the need for more research, he added.
Dr Morgan, Dr Grzybowski, and Dr Hirakata have disclosed no relevant financial relationships.
European Society of Retina Specialists 17th EURETINA Congress. Presented September 7, 2017.
Medscape Medical News © 2017 WebMD, LLC
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Cite this: Retina Specialists Seek to Stem Myopia Epidemic - Medscape - Sep 08, 2017.