Attempts to stop myopia progression: mixed bag: atropine works, exercises do not.
In particular, atropine eye drops significantly slow myopia by a mechanism that's still poorly understood. Hard contact lenses also may help. But eye exercises, orthokeratology, acupuncture, and a number of other interventions have no proven effectiveness, he said.
And your mother was right, said Dr. Fredrick of the university. Spending too much time doing near work or reading in the dark seem to hasten myopia's progression.
Numerous lines of evidence show that the development of myopia depends on a combination of nature and nurture. Myopia clearly has a genetic component, with a heritability index of 0.9. But genetic predisposition or not, myopia fails to progress as fast in children who don't engage in near work.
Several studies have shown that myopia rates tend to be low in rural populations, but tend to rise when these same populations move to the city. In schoolchildren, myopia progresses at about twice the rate during the school year as in the summer.
The near-work theory suggests that near work leads to retinal defocus in children who are genetically predisposed to myopia. Retinal defocus causes hyperopic defocus, which in turn results in a lag of accommodation, biochemical stimulus of the retina, and eventually axial elongation of the eye, and myopia.
Dr. Fredrick advised physicians to encourage their young patients to listen to what mothers have told their children for generations: Don't hold reading material too close, use adequate lighting, and rest for 10 minutes after reading for 30 minutes.
Over the years, numerous interventions have been suggested to slow the rate of progression.
Cycloplegics such as atropine have waxed and waned in popularity as a treatment for myopic progression. Popular in the 1970s, they are the subject of a resurgence of interest as the result of a number of controlled studies that demonstrate the value of this approach: While control groups progressed in their myopia at the rate of 0.24-0.91 diopters per year, patients using atropine eyedrops progressed at 0.05-0.14 diopters per year in various studies.
"Atropine might not just work by preventing accommodation," Dr. Fredrick said. "It might have some biochemical effect at the retinal/scleral interface."
The problem with atropine is that it has some side effects, although these are described as minimal in many studies. These side effects include blurring and photophobia, and there are fears that there also may be adverse long-term effects such as light-induced retinal damage and cataract formation.
Pirenzepine, a new drug now in clinical trials, seems promising. An antimuscarinic like atropine, pirenzepine causes minimal mydriasis and cycloplegia. It appears to have resulted in a 50% decrease in the progression of myopia in a phase II trial.
Some suggested that wearing glasses might actually increase the rate of progression, but this seems not to be the case. Bifocals have been extensively studied in randomized trials, and they do seem to provide some benefit--although this benefit appears to be minimal, Dr. Fredrick said.
Soft contact lenses don't slow the progression, but there's some evidence that rigid, gas permeable lenses do help. The results of a randomized, controlled study comparing these lenses with regular glasses will be released later this year, he said.
Orthokeratology, in which optometrists intentionally fit rigid contact lenses improperly in an effort to change the shape of the cornea, does not work. "Don't let your patients get it," said Dr. Fredrick, who noted that the procedure costs $3,000-$5,000.
Other interventions, some of which are highly touted on the Internet, in infomercials, and in radio ads, appear to be ineffective. There's no evidence for the efficacy of eye exercises such as the See Clearly Method or the Bates Method. Likewise biofeedback, ocular hygiene, and the scleral sling appear to do no good, he said.
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|Title Annotation:||Clinical Rounds|
|Date:||Dec 1, 2003|
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