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Nonsurgical treatments to prevent myopia development may be coming
Drugs to stop the progression of pediatric myopia are in the pipeline, one investigator says.
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There is currently no pharmacologic treatment to prevent pediatric myopia development, but R. Michael Siatkowski, MD, said he is confident that the future holds a solution.
| R. Michael Siatkowski |
Delivery systems, such as contact lenses, that could provide sustained drug delivery may be key to the drugs’ development, he said.
Dr. Siatkowski outlined and evaluated the current nonsurgical treatment options to prevent the development of pediatric myopia at the Pediatric Subspecialty Day during the American Academy of Ophthalmology meeting in Chicago.
“Optical intervention is basically ineffective,” he said. “Atropine is effective but has a lot of side effects and a significant rebound effect. Pirenzepine is about as effective as atropine with many fewer side effects. We do not have data on the potential rebound effect with this drug.”
Worldwide, there are 60 million myopic children, and the mean myopic progression is about 0.3 D to 0.5 D per year in whites, and twice that amount in Asians, Dr. Siatkowski said.
“I fully believe that within my years at practice we will have a commercially available agent for the retardation of pediatric myopia,” he said.
New solutions needed
Traditional optical interventions for the prevention of pediatric myopia include contact lenses, bifocals or progressive addition lenses. Dr. Siatkowski said there is a great deal of interest in new pharmacologic research because these optical treatments have demonstrated limited clinical effect on the progression of myopia.
One study comparing soft contact lenses to single-vision lenses found no significant difference in the annual rate of myopic progression between the two groups, he said.
“Many studies in the literature compare different powers of bifocals vs. single-vision lenses,” he said. “In different powers from +1.5 D to +2 D there is really no statistically or clinically significant difference in the myopic progression between these two groups.”
The Correction of Myopia Evaluation Trial (COMET) reported a statistically significant but clinically insignificant difference in progressive addition lenses vs. single-vision lenses, Dr. Siatkowski said. “However, a later [COMET] report did show that the effect on retarding myopic progression was greater in children who had a near esophoria,” he said.
Atropine
Atropine is the most widely studied and widely known pharmacologic agent for the prevention of pediatric myopia, Dr. Siatkowski said. Several other agents have been studied or are on the horizon.
Studies have shown that 0.5% atropine used on a daily basis could almost arrest myopic progression in children who used the drug for 1 year – a treatment that had superiority over multifocal or single-vision lenses, Dr. Siatkowski said.
“A very interesting study from Singapore used each patient as his own control. One eye was randomized to atropine and the other did not receive treatment. We found in this study that over a 2-year period the atropine eyes progressed by 0.25 D, compared to almost 1.25 D in the placebo eyes,” he said.
However, a follow-up study presented a concern of a significant rebound effect in the treated eye, Dr. Siatkowski said.
“These eyes became, on the average, more than 1 D more myopic in the first year after atropine was stopped compared to the typical rate of myopic progression in the control eyes,” he said.
Atropine also presents problems with cycloplegia, photophobia and phototoxicity, Dr. Siatkowski said.
“These kids have to wear bifocals and tinted lenses, and all of these factors lead to very poor compliance, and relative impracticability for the use of atropine on a regular basis for this effect,” he said.
Pirenzepine
Pirenzepine causes less mydriasis and less cycloplegia than atropine, Dr. Siatkowski said. Used in Europe as a treatment for peptic ulcer disease, the drug also has a wide safety profile, he added.
A study published last year showed a statistically significant difference in the rate of myopia progression in patients treated with pirenzepine vs. those treated with placebo. In the first year, the myopic progression rate of the treated group was 0.25 D vs. 0.5 D in the placebo group. The effects continued throughout the second year with treated patients progressing 0.5 D and untreated patients 1 D, he said.
“This study showed that 2% pirenzepine gel used twice daily can retard pediatric myopia over 2 years, and there was a very acceptable safety profile,” he said.
“A provocative side effect of this study is that it’s totally contrary to the accommodative pathogenesis of myopia because there was relatively little accommodative effect,” he said. “So it suggests that this drug, and perhaps atropine as well, work not by accommodation inhibition, but by sites on the retina or sclera.”
Inhibiting form deprivation
A young eye with ptosis or a vitreous hemorrhage that is not repaired can develop high myopia, Dr. Siatkowski said.
“It’s the image quality and presence rather than accommodative tone that is the mechanism for the development of myopia,” he said, “again suggesting a feedback loop between the retinal neurons and the factors that regulate the eye growth.”
Animal studies have shown that dopamine, a neuroreceptor, inhibits form deprivation myopia, Dr. Siatkowski said.
“Dopamine is involved in light/dark adaptation, certainly in circadian rhythms, and one of those such rhythms in humans includes the shedding of the rod outer segments. It’s also known that highly myopic eyes have abnormal dopamine cycles on a diurnal basis, so this could be a potential area of future research for prevention of pediatric myopia,” he said. “However, the fact that it’s hard to deliver to certain sites in the eye, and there’s potential toxicity, have limited its use in humans so far.”
For Your Information:
- R. Michael Siatkowski, MD, can be reached at Dean A. McGee Eye Institute, 608 Stanton L. Young Blvd., Oklahoma City, OK 73104; 405-271-1094; fax: 405-271-3013; e-mail: rmichael-siatkowski@dmei.org. Dr. Siatkowski is a consultant to Valley Forge Pharmaceuticals, maker of pirenzepine.
- Daniele Cruz is an OSN Staff Writer who covers all aspects of ophthalmology.