For children diagnosed with worsening myopia, bifocals might be a better choice than standard lenses for nearsightedness; researchers have found that the condition doesn't seem to progress as rapidly among bifocal-wearing children.
Those findings, released Monday, raise the intriguing question of whether there is a better way to treat myopia early in its course, slowing its typical progression.
The condition, in which near vision is clear but distance vision is blurry, is usually identified in childhood and worsens until late adolescence. Myopia is increasing worldwide, with researchers at the National Eye Institute reporting last month that rates in Americans ages 12 to 54 rose 66% in the last 30 years.
Some research had suggested that treating children with bifocals could reduce the ultimate severity of the condition. Bifocals are glasses that use two corrective powers in each lens; traditional glasses simply correct vision for one distance.
In the new study, researchers studied 135 Chinese Canadian children who were diagnosed with progressive myopia, meaning myopia that had worsened significantly over the previous year. The children, whose average age was 10, were assigned to wear either single-vision lenses, bifocals or bifocals with prism, a type of correction that is ground into lenses to help the eyes work together and enhance near vision.
After two years, researchers found the progression of myopia was most rapid among those who wore single-vision lenses. The slowest rate of progression was among children who wore prismatic bifocals -- a 58% difference in the rate of progression compared to children wearing single-vision lenses. There was a 38% difference in the rate of progression between users of standard bifocals and users of single-vision lenses.
The study was released online Monday and will appear today in the Archives of Ophthalmology.
"By limiting their study to those children who were progressing rapidly, they have found a group that can be more effectively treated," said Thomas A. Aller, an optometrist in San Bruno, Calif., who was not involved in the study but has studied myopia treatment.
Bifocals may help slow myopia by enhancing both near-distance visionand distance vision and by reducing eye strain. But researchers don't know if the effects of the treatment will last. If the effects are permanent, bifocals for rapid-progression myopia could reduce the number of people who end up with severely impaired vision.
"Myopia is associated with conditions such as glaucoma and cataract, and is an important risk factor for retinal detachment," said Desmond Cheng, the lead author of the paper, in an e-mail. He is an optometrist at Hong Kong Polytechnic University. "With higher myopia prevalence and an aging population, these myopia-related pathologies are also likely to increase in the coming decade."
The benefits from traditional and prismatic bifocal lenses weren't spectacular. But, Cheng said, the treatment should be an option for myopic children.
"The modest benefit should be weighed against factors such as the increased cost of the lenses, poor cosmetic appearance and attitude of the parent and child if bifocal spectacles are to be prescribed for the purpose of controlling myopia," he said.
Aller said other studies suggested that soft, bifocal contact lenses might yield more benefit in slowing myopia progression than bifocal glasses and would be better tolerated by children and teenagers. Because contact lenses correct vision around the periphery of the cornea better than eyeglasses, they may even be more effective at slowing myopia progression.
Aller said numerous vision companies were working on myopia products. "There ought to be treatments soon to slow the progression of nearsightedness," he said.