Elaine was worried. Her daughter Brittany first started wearing glasses two years ago when she was in third grade and then last year they needed to be made stronger. Now, on this visit to the eye doctor, she was told that Brittany needed an even stronger prescription.
She expressed her concern to the eye doctor and was assured that this was normal and not to worry. "She won't go blind, but she just will probably need to have stronger glasses every year or so for some time to come. Often times eyes our eyes don't stop changing until stop growing and reach our early twenties."
It is true that the average increase in myopia is about -.50 dioptors of change a year. Over the years many attempts have been made to prevent this from happening, but nothing has been particularly successful.
The statistics of myopia are truly frightening. All over the world myopia is getting worse. Myopia has increased by 66% in the US over the past 30 years and now more than 40% of individuals from 8 to 54 are myopic. In Singapore 80% of high school children are myopic. It is a true epidemic - over a billion people in the world are affected by myopia.
Exciting new research tells us for the first time what causes myopia and we are now beginning to figure out ways of slowing it down and even preventing it. But the treatment works best when it is started at the earliest stages of myopia.
Myopia can be thought of as an eyeball being too long for its focus. When light focuses in front of the retina instead of on the retina the image is fuzzy. Spectacle and contact lenses shift the focus back to where it belongs, which restores the sharpness of the image.
But how does the image, in normal individuals, ever stay focused where it belongs as the child's eyes grow? Research shows that the eye has the means to adjust itself to the proper focus. This process is called emmetropization, and it is driven by a proper focus in the peripheral retina. That is, it only works well when the peripheral (off center) focus is not "over-focused".
Unfortunately, in many individuals, when the central "on-center" image is focused clearly (as when looking at the eye chart) the peripheral focus is "over-corrected"; the periphery of the lens is too strong. We now know that this causes an increase in the myopia.
Traditional glasses and contact lenses have the same focus over the entire lens. Bifocal glasses have a different focus at the bottom of the lens for reading, but only at the bottom.
There are special multifocal contact lenses that have the proper less strong focus 360 degrees around the lens. A recent study of 122 children showed that these lenses slowed the increase in myopia from -.50 diopters per year to -.03 diopters, an insignificant increase. But even though these lenses can slow down or even stop the increase in myopia, they cannot reverse a myopia that has already occurred.
The most exciting recent technology is orthokeratology - the means of using special eye molds to reshape the eye to the proper focus. They are only worn at night and removed during the day. There are some limits to the amount of correction that can be achieved, so it is best to start the treatment program before the myopia becomes too advanced.
Dr. David Littlefield
