Concern for myopia progression increases with alarming rise in global prevalence

As one of the most common eye disorders around the world, myopia has dramatically increased in prevalence throughout the years, starting at younger ages than ever before.

Globally, high myopia is ranked second as the leading cause of visual impairment, with 10% of all myopes having 6 D of refractive error or more, according to Liu and colleagues.

Foster and colleagues reported that myopia has nearly doubled in the last 30 years in the U.S., going from a prevalence of 25% in 12- to 54-year-olds in 1983 to 42% more recently.

Smith and Walline wrote in a review in Adolescent Health, Medicine and Therapeutics that in East Asia, nearly 50% of urban populations are myopic, while the prevalence in university student populations is approximately 90%. The rate of progression is fastest in young children and approximately 0.5 D per year across various ethnicities. Younger age at onset has been linked to faster progression, which leads to increased myopic severity, they said.

Myopia and high myopia will affect nearly 5 billion and 1 billion people, respectively, by 2050, according to Monica Jong, PhD, a researcher at the Brien Holden Vision Institute, and colleagues. This staggering increase will have important implications for eye care services and managing and preventing myopic-related ocular complications and vision loss, according to the researchers.

Additionally, they discovered that the majority of myopia is found in those younger than 40 years, which they attribute to lifestyle changes for children and young people over the past 10 to 25 years, especially in the large population centers of Asia.

Image: Smith EL

Higher amounts of myopia are associated with an increased incidence of glaucoma, retinal detachment, macular choroidal degeneration, myopic choroidal neovascularization, myopic retinoschisis, as well as early-onset cataract, amblyopia and strabismus, Smith and Walline said.

Environmental, demographic, genetic factors

Research evidence is growing to attribute a complex system of factors to myopia development such as: parental myopia and ethnicity, environmental factors, peripheral refraction and binocular vision, Paul Gifford, PhD, FAAO, lecturer and researcher at the University of South Wales, School of Optometry, said in an interview with Primary Care Optometry News.

French and colleagues, in a study published in Eye, explored the relationship between being myopic and time spent outdoors, hours of near work per week, myopic parents and ethnicity in Australian children. Children who spent low amounts of time outdoors and performed high levels of near work, at a mean age of 6 years, had significantly greater odds of myopia by 12 years of age. Researchers found a similar pattern within older children who experienced less time outdoors and more near work at an average age of 12 years: they had an increased risk of myopia by age 17.

As for ethnicity, those of East Asian heritage had a significantly higher incidence of myopia and spent significantly less time outdoors and more time on near work than European Caucasian children, according to the researchers. Generally, the prevalence of myopia is highest in Asian populations, followed by Hispanic, African American and, lastly, Caucasian populations.

According to the study, prevalence of myopia in Australian schoolchildren was reported to be 42.7% and 59.1% in 12- and 17-year old children of East Asian ethnicity, respectively, compared to only 8.3% and 17.7%, respectively, in European Caucasian children of the same age.

Only 7.8% of children without a myopic parent became myopic, whereas 21.4% of children with one myopic parent and 22.0% of those with two myopic parents did so, according to French.

Furthermore, in this analysis, having a less hyperopic refraction at baseline was the most significant predictor of incident myopia in the younger and older cohorts.

Geographic location may also play a role in the prevalence of myopia. For example, a study reported a myopic prevalence rate of 16.2% in children in rural areas vs. more than double that amount in cities such as Guangzhou and Hong Kong, with prevalence rates of 38.1% and 36.7%, respectively, Foster and colleagues reported.

Younger age at myopia onset may also contribute to high myopia. According to Smith and Walline, myopia typically develops at approximately 8 years of age and progresses through 15 to 16 years of age at an average rate of approximately 0.5 D per year. Conversely, those who develop myopia later in life do not face the same severe progression rate as adolescents.

A study in Eye from Goldschmidt and Jacobsen suggests that diet and diabetes may factor in myopia development as well. Researchers discussed a previous study indicating an association between hyperglycemia and myopia, whereas the insulin dosage was not associated with refractive error. The study confirmed that myopia is more prevalent in patients with diabetes than in those without.

“The underlying mechanism of the refractive changes remains unclear, but the study did support a relation between impaired metabolic control and myopia,” the researchers wrote.

Goldschmidt also highlighted the significance of physical activity, which was dependent on whether or not the activity occurred outside; indoor sports were not protective against the development and progression of myopia.

The impact of education weighs on myopia as well, with student myopia 10 times higher than among unskilled workers, based on previous Danish studies highlighted by Goldschmidt. Myopia rarely occurs in less educated populations, according to the researchers.

Available treatments

Various management options currently exist for myopia, such as pirenzepine 2% gel, deliberate optical undercorrection, increased outdoor activity and sunlight exposure, refractive surgery, as well as bifocal and progressive eyeglasses or contact lenses.

It is thought that undercorrection of myopia can reduce accommodative effort and lag, thus, reducing myopia progression, when, in actuality, it leads to either an increase or no effect on myopia progression, according to Smith and Walline.

Although they are not FDA approved, Gifford said the use of varying concentrations of atropine eye drops have also been studied in recent years.

The goal of a myopia control contact lens is to prevent the eye from reaching high myopia, which is worse than -5 D, according to Jong, so that the risk of developing sight-threatening complications is reduced.

“It is becoming increasingly evident that progression of myopia is multifactorial, and causes for its development are frustratingly difficult to nail down to an individual level,” Gifford explained. “Specifically, in terms of contact lenses, the questions we still need answered are over what duration a myopia controlling correction needs to be worn and when is the best time for wear to commence.”

Orthokeratology

Essentially, orthokeratology (ortho-K) and soft multifocal contact lenses have shown the best consistency with the least amount of side effects. However, clinical and academic acceptance of these treatments has been restricted due to data limitations, required off-label usage and an absence of clear understanding associated with the lenses, Gifford told PCON. The main risk of overnight ortho-K is the potential for infection in the closed eye. However, gas-permeable (GP) lens materials are known to be some of the safest, he said.

“Retrospective studies reported in the literature have suggested that this risk is no greater than any other modality of overnight contact lens wear and likely to be less because of the rigid material,” Gifford said.

“Ortho-K wasn’t designed to control progression of myopia; however there is now a growing body of evidence from scientists across the world showing that it is effective in slowing progression of myopia in children,” he continued. “There is also growing literature showing that soft multifocal contact lenses, particularly those of center distance design, are effective for myopia control.”

Researcher and professor Helen A. Swarbrick, PhD, and colleagues have studied the effects of ortho-K lens wear on axial length growth. In a group of patients wearing ortho-K lenses overnight in one eye and conventional GP lenses in the other eye for 6 months, axial length showed no change in the ortho-K eye but had increased by 0.04 mm in the GP eye. At 12 months, after lens-eye combinations were reversed, again there was no change from baseline in axial length in the ortho-K eye.

Earl L. Smith III, OD, PhD, FAAO, and colleagues have advanced the hypothesis that peripheral retinal focus predominates over foveal focus in driving growth of the eye in children, Swarbrick told PCON. In particular, peripheral focus behind the retina (hyperopic defocus) stimulates eye growth (and, thus, myopia progression), whereas peripheral myopic defocus inhibits eye growth in the developing eye.

From Swarbrick’s research it is now understood that overnight ortho-K induces rapid change to peripheral myopic defocus within 1 to 2 weeks with lens wear.

Swarbrick said that manipulation of ortho-K lens parameters to optimize myopia control for individual children is a complex challenge, as it is constrained by the need to maintain central focus to provide good vision. She is currently conducting research to understand how the shape of the retinal image shell can be manipulated by modulating the shape of the anterior surface of the eye’s optical system. She and her colleagues are also using a GP miniscleral lens platform and modifying parameters of the anterior surface of the lens with the goal of modulating the retinal image shell.

“These exploratory short-term studies will help us develop insights into the most effective approaches for customizing corneal reshaping in order to optimize myopia control outcomes with this modality,” she said.

She added that further evidence from longer-term studies of overnight ortho-K is needed as well as more information about the risks of rebound and the extent of myopia control benefits after discontinuing overnight ortho-K.

Other optical strategies

To improve lens designs, the basic parameters of how wear influences the efficacy of a given lens need to be understood, according to Smith, who is dean of the University of Houston College of Optometry, in an interview. “We are just scratching the surface; however, the exciting thing is we have commercially available lenses now that are producing a 40% to 50% effect in reducing the progression of myopia, and I think we can get a lot better than that.”

According to a review published in Optometry and Vision Science by Gifford, the ideal myopia-controlling contact lens should:

• induce peripheral myopia without compromising vision;

• reduce lag of accommodation;

• reduce near esophoria;

• provide controlled release of antimuscarinic agents;

• provide a beneficial shift in positive spherical aberration to improve near point depth of focus without compromising image quality.

“The main area for development is going to be in soft lenses, because the majority of wearers use these lenses, and practitioners are confident in fitting them,” Gifford told PCON. “Ortho-K is believed to induce a myopia controlling effect through the optical profile it provides to the eye, but there is still much to learn about this mechanism and how it may influence the visual function of each individual.”

“On the optical side we are now seeing novel lens designs,” Smith added. “For example, extended depth of field designs have a lot of potential promise not just for presbyopia, but anti-myopia. I expect to see new contact lens designs, new ortho-K lenses designed for relatively low myopia and certainly atropine-like agents coming back on the market in force.”

Pharmacological intervention

A significant amount of literature to date focuses on the safety and efficacy of atropine eye drops to slow myopic progression.

The Atropine for the Treatment of Myopia (ATOM) phase 1, 2 and 3 clinical trials, published in Ophthalmology (Chia, et al.), compared the safety and efficacy of different concentrations of atropine eye drops in controlling myopia progression over 5 years.

At 3 years, atropine 0.01% resulted in being the most effective; therefore, 24%, 59% and 68% of the atropine 0.01%, 0.1% and 0.5% concentration groups, respectively, were required to restart atropine 0.01%. Younger children and those with greater myopic progression were more likely to require retreatment, the study said.

The 76% of children who did not require retreatment in the 0.01% group after year 3 continued with a persistent response in reduced progression; had the lowest overall myopia progression and change in axial elongation; and had minimal pupil dilation, minimal loss of accommodation and no near visual loss compared with the higher doses at the end of the 5-year follow-up.

With atropine 0.01% being the lowest dose tested thus far, studies are showing it has minimal side effects while still reducing the rate of myopia progression by 50% to 60%.

Additionally, a study by Clark and colleagues evaluated atropine 0.01% in an ethnically diverse population of 60 myopic children, in which the drug significantly reduced the rate of myopic progression over 1 year with minimal side effects. The study suggested that atropine 0.01% was most effective in children with low initial myopia, but that it may not control rapid myopic progression in some patients.

“It may be that we can identify dosing strategies that [are safer], such as a drop every other day or just on the weekends, which would greatly reduce the potential of long- and short-term complications,” Smith said.

In a meta-analysis from Ophthalmology, Huang and colleagues found that high-dose atropine (1% and 0.5%), moderate dose atropine (0.1%) and low-dose atropine (0.01%) showed the strongest effects in myopia control. Pirenzepine, ortho-K, peripheral defocus modifying contact lenses, cyclopentolate and prismatic bifocal spectacle lenses showed moderate effects, according to the study.

Another potential pharmaceutical treatment, 7-methylxanthine, shows promise and is now being investigated in a significant way, according to Smith. The drug is approved as an oral tablet to control myopia progression for children in Denmark, he said.

Public health consequences

Overall, myopia carries an estimated economic burden of $2 billion annually, Liu and colleagues reported.

“Our work shows that if no action is taken, myopia will affect half of the world population by 2050, and high myopia will affect nearly 10% of the population,” Jong told PCON.

Gifford suggested that the biggest need at the moment is not in research, but in practitioner involvement. “We already have a number of contact lens options readily available, yet we are not seeing an increase in uptake that we would expect given the increase in childhood myopia,” he said.

Jong raised similar concerns, “Optometrists will need to spend some time educating the child and their parents about why they would want to prevent myopia and the options to help the child and parents comply with any management strategies.”

Having local health authorities and governments engaged in the plan to combat myopia will have substantial impact, Jong added.

“For example, in order to prevent the onset of myopia we need to target young children earlier than 5 to 6 years, and to reach these children, community interventions through health and government authorities are critical,” she said.

Worldwide, governments in various countries are starting to update laws. “For example, in Taiwan and Singapore, there are health campaigns on TV and on billboards telling children to spend more time outdoors,” Jong explained.

In addition, schools in China and Taiwan have slowly integrated longer recess time for students, she explained. In China they are experimenting by holding classes in glass classrooms. She also noted the existence of a fine in Taiwan for parents who allow their children to use near devices for a prolonged time.

Jong believes governments in other parts of the world will look to what has been done in East Asia as an example.

Specifically, engaging education departments would be the best way to change behaviors/lifestyle earlier on, including more outdoors time and by building classrooms that have better illumination and ergonomics, she said.

Appropriate management means screening all children at preschool age and then at different intervals to help catch refractive errors and other ocular conditions early, Jong continued. Governments would need to look at an integrated approach with other activities, promoting eye health together with anti-obesity and sun protection to be most effective.

“In 5 to 10 years, the public will know the term ‘myopia’ and will even ask for myopia prevention and control when they visit an optometrist,” she said. “They will want to access the best performing products in terms of efficacy, vision and comfort and expect that this is a service that requires expertise and not something they can go to the Internet for in terms of diagnosis, management and treatment.

“Myopia will be a growing concern due to the modern lifestyle increasingly taking place indoors, being mostly near-based and unlikely to change in the future,” Jong added. “Optometrists will play a leading role in myopia management, encompassing not only the clinical aspect, but educating and advocating the need to treat myopia as more than a simple refractive condition.” – by Abigail Sutton and Kristie L. Kahl

• References:
• 7th Annual Berkeley Conference on Translational Research http://optometry.berkeley.edu/research/bcsdp-clinical-translation-conference-2013.
• Chia A, et al. Ophthalmology. 2015;doi:10.1016.j.ophtha.2015.07.004.
• Clark TY, et al. Clin Exp Pharmacol. 2015;doi:10.1089/jop.2015.0043.
• Foster PJ, et al. Eye. 2014;doi:10.1038/eye.2013.280.
• French AN, et al. Ophthalmology. 2013;doi:10.1016/j.ophtha.2013.02.035.
• Gifford P, et al. Optom Vis Sci. 2015;doi:10.1097/OPX.0000000000000762.
• Goldschmidt E, et al. Eye. 2014;28:123-133.
• Holden BA, et al. Ophthalmology. 2016;doi:10.1016.j.ophtha.2016.01.006.
• Holden BA, et al. Clin Exp Optom. 2015;doi:10.1111/cxo.12339.
• Huang J, et al. Ophthalmology. 2015;doi:10.1016/j.ophtha.2015.11.010.
• Jones LW, et al. Optom Vis Sci. 2015;doi: 10.1097/OPX.0000000000000700.
• Liu YM, et al. Eye & Contact Lens. 2016;doi:10.1097/ICL.0000000000000219.
• Smith MJ, et al. AHMT. 2015;doi:10.2147/AHMT.S55834.
• Swarbrick HA, et al. Ophthalmology. 2015;doi:10.1016/j.ophtha.2014.09.028.

• For more information
• Paul Gifford, PhD, FAAO, can be reached at p.gifford@unsw.edu.au.
• Monica Jong, PhD, can be reached at m.jong@brienholdenvision.org.
• Earl L. Smith III, OD, PhD, FAAO, can be reached at esmith1@central.uh.edu.
• Helen A. Swarbrick, PhD, can be reached at h.swarbrick@unsw.edu.au.

Disclosures: The Brien Holden Vision Institute (BHVI) has patents in myopia control. Gifford reports no relevant financial disclosures. Jong is employed by the BHVI. Smith has patents related to anti-myopia lens designs and receives royalties for a spectacle lens design from Zeiss. Swarbrick’s research is supported by the Australian government through the Australian Research Council Linkage Project Scheme, with industry partners Bausch + Lomb Boston (U.S.), BE Enterprises and Capricornia Contact Lens (Australia). Swarbrick has received in-kind support from Bausch + Lomb (Australia), Paragon Vision Sciences and CooperVision.