Dear Doctor: Our son recently went to the optometrist, and we were surprised to learn he has astigmatism and needs glasses. My friends say astigmatism is common, but that it means he'll never be able to wear contacts. Is this true?
Dear Reader: Your friends are both right and wrong. Yes, astigmatism is a common condition that occurs when part of the eye is not symmetrical. Instead of being perfectly round, the cornea -- we'll talk more about this in a minute -- is shaped more like a football. And no, having astigmatism doesn't automatically mean you can't wear contacts.
Let's start with a bit of anatomy.
The human eye is a remarkable organ that is made up of more than 2 million working parts. Your eyes see light, shape, color, depth, distance and motion. They can focus on something a few inches from your face, on objects that are miles away and can detect peripheral motion in a surprisingly wide radius. Of all the organs in the human body, only the brain is more complex.
Our eyes are so crucial to our survival that they are seated deep within the protective casing of the skull. Only about 15 percent of the entire eye is visible. The visible parts are the mechanisms that admit and control light, much like a camera. And that's where astigmatism comes into play.
The clear, dome-shaped surface of the eye is called the cornea. Behind it sits the iris, the colored part of the eye, which controls the size of the pupil. As light passes through the cornea, it bends, moves through the pupil and bends again as it passes through the lens.
When the cornea is round, incoming light hits just the right spot on the lens. The lens then sends a perfect image to the retina, a thin bit of tissue at the back of the eye. The retina is embedded with millions of receptor cells, which translate incoming light into the signals that the optic nerve will send to the brain.
When the cornea is less than perfectly round, this is known as astigmatism. Incoming light misses the target area of the lens and the retina gets an imperfect image. The signals sent to the brain are then interpreted as blurred vision.
The good news is that astigmatism is easily corrected with prescription eyeglasses. And while at one time individuals with astigmatism couldn't wear contact lenses, technological advances have made it possible.
Due to the asymmetry of the cornea, correction for astigmatism is directional. That is, the corrective lens must sit at a certain angle. Thanks to new technologies, contact lenses are now "weighted." Instead of spinning out of focus with every blink, the thicker bottom edge settles into place for optimal correction. Your optometrist can tell you whether contacts are an option for your son's particular kind of astigmatism.
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