High myopia: Global pandemic with genetic and environmental causes

January 19, 2016

Singapore-The manner in which myopia works has been a mystery until recently when investigators began making inroads into how the disease progresses. This knowledge likely is going to result in lifestyle changes, said Jodhbir Mehta, MBBS, PhD.

Singapore-The manner in which myopia works has been a mystery until recently when investigators began making inroads into how the disease progresses. This knowledge likely is going to result in lifestyle changes, said Jodhbir Mehta, MBBS, PhD.

“Myopia is the most frequent cause of distance impairment in the world and it is creating an alarming global [pandemic] with deleterious ramifications for the quality of life and economic health of individuals and nations as a whole,” said Dr. Mehta,, associate professor, Singapore National Eye Centre, and head of Corneal and External Eye Disease Department.

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The data are alarming, with almost 22% of the current world population affected. This translates to about 1.5 billion people.

In light of this, Dr. Mehta’s perspective on the disease has changed over time, that is, from his view when he practiced in the United Kingdom that the average degree of myopia of about -3.0 D could be managed with a refractive procedure to recognition of the fact that the average level in Singapore is now -6.0 D. A startling statistic is that almost 80% of the 18-year-olds who enlist in the army in Singapore are myopic.

“My current thinking is that the prevalence of myopia is rising dramatically, i.e., to 60% to 70% in many East Asian countries and 25% to 40% in Western countries,” he said. “It is more concerning that pathological high myopia exceeding -6.0 D ranges from 6.8% to 38% in Asia.”

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Myopia has doubled in the United States in the past 30 years and the prevalence of myopia over -8.0 diopters has increased eightfold, he added.

“In China, 75% of people in the 15- to-24-year age range have myopia and 10% have over -6.0 D,” Dr.Mehta said.

Concerns

 

The concerns with these statistics are the numerous blinding problems that result from myopia, which are associated with high levels of the disease. These blinding disorders are increasing worldwide-not just in Asia.

The economic impact of this global pandemic is considerable, Dr. Mehta related.

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Problems for individuals with high myopia, he said, include:

·       Unsuitable jobs for those with uncorrected refractive errors

·       The cost of treatment with optical devices or refractive procedures

·       The need for frequent long-term follow-up

·       The compromised quality of vision even among those without a myopia-related pathology

Dr. Mehta explained further that the earlier that myopia starts, the greater the burden.

“We are seeing a shift to younger onset of myopia, which is especially concerning because younger eyes have more rapid progression of myopia,” he said.

Analyzing the causes and prevention

 

Analyzing the causes and prevention

There is, of course, a genetic component to myopia that is uncontrollable. In Asia, this carries an odds ratio of greater than 11 times; the risk also increases by 2% to 5% in children with two myopic parents. Monozygotic twins also have a higher risk than dizygotic twins.

Environmental causes of myopia are being recognized as having a secondary role in disease development, with excessive near work activity (studying and use of electronic devices) and too little outdoor activity. In fact, increasing outdoor activity exerts a protective effect against the development and progression of myopia, possibly because of an effect of light intensity, possibly the ultraviolet spectrum, and vitamin D.

Dr. Mehta advises parents to monitor how their children read, that is, by keeping books 30 cm away, using sufficient lighting, sitting back from the computer, taking regular breaks, and increasing outdoor activities.

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“These interventions can actually reduce the rate of myopia development,” he said. “However, the rate of myopic progression is not affected.”

The most effective way to reduce myopic progression is instillation of an anti-muscarinic topical medication, such as atropine.

However, the drawbacks to this approach are considerable: light sensitivity, near blur, and preclude use of these medications, in addition to the fact that they are not commercially available or FDA approved. A recent Singapore National Eye Center study of three doses of atropine showed that a low dose (0.01%) may slow myopic progression by about 50% to 60% and was associated with fewer side effects compared with the 1% dose.

Treatment options

 

Orthokeratology contact lenses that are worn overnight are an effective treatment option, with recent results showing the elongation of axial length slowing down 40% to 50%. The disadvantages are cost and risk of infection.

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Dual-focus contact lenses that are worn during day are another effective option that is associated with decreased myopic progression of 30% to 40%, Dr. Mehta explained.

“Myopia is becoming a global [pandemic], with rates increasing in Asia and the West,” Dr. Mehta said. “Lifestyle factors, computer use, and urbanization are causing the increasing rates.

“It is unlikely that it will be possible to eliminate myopia, but it is possible to reduce progression to pathological high myopia that is associated with more severe complications and blindness,” he added. “A recent study seemed to advocate use of low-dose 0.01% atropine to reduce progression with minimal side effects.”