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More financial, human capital needs to be invested to reduce burden of high myopia
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In the early 1980s, I became interested in the surgical treatment of myopia as a surgeon in the Prospective Evaluation of Radial Keratotomy study. In this study, we were treating patients with low to moderate myopia. While there is room for disagreement, I categorize –0.125 D to –3 D as low myopia, –3.125 D to –6 D as moderate myopia and over –6 D as high myopia. Going all the way back to Sir Stewart Duke-Elder, myopia over –6 D has been considered “pathologic myopia,” and these are the patients who have significant visual disability as well as increased risk for many other comorbidities, including early-onset cataract, retinal tear, retinal detachment and glaucoma.
While any imbalance between the refractive power of the cornea and/or lens and the axial length of the eye can result in myopia, high myopia is usually axial myopia with an axial length longer than 25 mm. When I was doing my literature research on myopia in 1980, several studies, including the National Health and Nutrition Examination Survey, found the prevalence of myopia to be approximately 25% in the U.S. Another 25% were hyperopic and 50% emmetropic. Approximately 30% had 1 D or more of astigmatism and 35% were presbyopic. Over the ensuing 35 years, the number of myopes and presbyopes has increased to more than 40%. Europe has noted a similar increase in myopia. Most impressive is the increase in myopia in Asia, where in some countries, such as Singapore and China, it has risen to more than 80% in the younger population.
Something is definitely at work here. The increasing number of presbyopes is easy to explain with an aging population, but what is causing this epidemic of myopia? I usually look first at genetics and then at environment. In general, I am impressed that our genes are usually more important than our environment, but the genetic pool of humanity has not significantly changed in the past 35 years. It has to be environmental. The epidemic of obesity and diabetes can largely be explained by environmental factors, including a high-fat, high-sugar, high-calorie diet and a sedentary lifestyle. In regard to myopia, I am a believer that the causal factor is the extraordinary shift in our visual tasks from distance to near as we spend more years in school and adopt to a more near-dominant lifestyle, including hours on the cell phone and computer.
Hunter-gatherer populations remain primarily emmetropic and hyperopic. It is the societies where children spend hour after hour studying for the first 20 to 30 years of their life, and then assume an occupation dominated by even more near vision tasks, that have seen the explosion in myopia. To me it is evolution at work, adapting our visual system to the task at hand. This is arguably a good adaptation up to –2 D to –3 D, but unfortunately the process all too often continues into the over –6 D of axial myopia, which is less functional for everyday activities and associated with meaningful sight-threatening comorbidity.
In the PERK study, the second eyes not operated with mild to moderate myopia progressed about 1 D in 10 years. That is a 0.1 D per year progression. Today, studies suggest that starting at school age, many myopes are progressing at a rate of 0.5 D per year. In a decade, that is 5 D today vs. 1 D in a decade progression noted in young adults 35 years ago. Appropriately so, parents are concerned and looking for a treatment. Most promising to date is low-concentration 0.01% atropine sulfate topical drops. In the recent landmark Atropine for the Treatment of Myopia study, 0.01% atropine was well tolerated and statistically and clinically significant in its ability to retard myopia progression.
Atropine treatment is not new, and the theory is that heavy accommodation demands lead to progressive myopia. I remember listening to Dr. John Dyer from the Mayo Clinic discuss atropine and bifocals for the treatment of progressive myopia when I was a resident at the University of Minnesota in the late 1970s. He was using full cycloplegia, and the morbidity of living with an 8-mm pupil and the need for unattractive bifocal glasses to read made this treatment impractical for most children. Still, his data 40 years ago showed that it worked. The amazing and unexpected outcome of the ATOM study is that very dilute atropine that only increases pupil size about 1 mm and retains functional accommodation is also clinically effective.
While controversy remains, it is likely time to start offering this treatment to select children, especially those who have two parents with pathologic high myopia, a near-dominant environment and evidence of rapid myopia progression. The other lifestyle changes that can be recommended include a daily period of distance-dominant outdoors activity. This includes most sports and playground activities. No form of visual training has been proven effective. Glasses and contact lenses neither accelerate nor retard myopia progression and should be prescribed and worn as needed for daily activities. Orthokeratology is recommended by some, but it only temporarily flattens the cornea with no effect on progressive axial length change. Also, keratitis is not infrequent and sometimes sight-threatening.
In regard to refractive surgery, I find myself counseling patients interested in corneal refractive surgery to wait until there is good evidence of refractive stability, which often does not occur until after their college and professional school demands for near vision tasks are reduced. Although in select cases I will perform LASIK/PRK in patients as young as 18 years of age, I much prefer operating on those in their mid-20s or later. Fortunately, most patients are near 30 before they seek an alternative to their glasses and contact lenses.
More investment of financial and human capital is to be encouraged to look for ways to reduce the burden of high myopia on the individual and society. While we have many effective methods to correct low to moderate myopia, and an increasing number of myopic patients is in some ways an asset to our practices, we do not want 50% or more of our population to be over –6 D in 2050 with the associated functional disability and sight-threatening comorbidities. Unless something changes, that seems a likely probability.