Myopia Control
Myopia, or nearsightedness, is a big problem for many children. This difficulty with distance vision interferes with many daily activities, including learning at school. And as they grow, many children experience progressive myopia, which means the problem gets worse over time.
Can anything slow or stop the progression of myopia? Eye doctors and other researchers have studied this question for some time. Here's the scoop on the various strategies they have tried:
Using Rigid Contact Lenses
Over the years, several studies seemed to indicate that myopia could be controlled by wearing rigid gas permeable or RGP contact lenses. (Now more eye care practitioners are calling them GP contact lenses.) The idea was that the rigid contact lens would act as a splint to fortify the front of the eye without affecting the overall corneal shape. The lens would reduce myopic progression, as compared with wearing eyeglasses or soft contact lenses.
This idea was controversial, and some eye care practitioners scoffed. Since many of the studies were flawed because of inadequate controls of important variables, incomplete follow-up and poor selection of study participants, their results were inconclusive.
Finally, the Contact Lens and Myopia Progression (CLAMP) study published its findings in 2004. The CLAMP study, funded by the National Eye Institute, followed myopia progression in more than a hundred children aged 8 to 11 over a three-year period. Some wore rigid GP contact lenses, while others wore soft lenses. The researchers measured the participants' visual acuity as well as the physical growth of their eyes. In myopic people, the eyeball grows longer than normally, with a steeper cornea; this longer axial length is what causes the blurred distance vision.
The GP lens wearers did show less myopia progression, but it was only temporary. Their eyes continued to grow as long as the eyes of the soft lens wearers, and since the GP lenses were not able to slow or stop the growth, they could not provide permanent myopia reduction. A clinical trial conducted in Singapore reached a similar conclusion.
One difficulty in proving that wearing GP lenses definitely retards myopia lies in not knowing how nearsighted someone would be without such treatment. It's not an exact science: practitioners can't say that your child would have progressed to a prescription of -8.50 diopters if he hadn't worn GP lenses to control myopia. On the other hand, myopia does seem to run in families, and if most of the family members are very myopic, it's not unreasonable to suppose your child will eventually become very myopic as well.
Undercorrecting Myopia
Some eye doctors have tried undercorrecting nearsightedness, in hopes of reducing near focusing strain that has been suggested as a cause of progressive myopia. A recent study failed to support this idea, finding no statistically significant difference between those who received full correction and those who received undercorrection. Two other studies found that undercorrecting nearsightedness actually increased the rate of its progression.
Another study, the Correction of Myopia Evaluation Trial (COMET), has been testing the idea of using eyeglasses with bifocal lenses or progressive lenses to reduce the eye focusing needed for sustained near vision. So far it has found that progressive lenses, compared with regular single vision lenses, did slow myopia progression in children by a small, statistically significant amount during the first year. But the effect wasn't significant in the next two years.
Undercorrecting myopia is therefore not a proven strategy for slowing the progression of nearsightedness in children. It also has the disadvantage of causing blurred distance vision if the treatment is performed with single vision lenses.
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