Are you near-sighted or far-sighted?
“Doc, I can’t see things far away, so that means I’m far… No, wait, near-sighted….?” (I usually hear something resembling this comment daily.)
Let’s break it down:
Think of the eye as a camera. The camera lens focuses the image that you are photographing onto the film. In the human eye, the natural lens and cornea in the front of the eye focuses the images we see onto the back layer of the eye, called the retina. What could keep this from happening properly? To simplfy: the length of the eyeball.
Myopia (aka ‘near-sightedness’). In myopia, the eyeball is longer than it should be. This means when a myopic person is gazing at an object far from them, the image comes into focus in front of the retina and appears blurry. If they move closer to the object, that point of focus within the eye moves farther back until it focuses on the retina, and the person sees clearly. The more myopic a person, the closer he or she must hold something to see it clearly.
Hyperopia (aka ‘far-sightedness’). In hyperopia, the eyeball is shorter than it should be. This means that when a hyperopic person is gazing at an object far from them, the image comes into focus behind the retina. Theortically, people with hyperopia should have difficulty seeing at both distance and near. However, (and here is the tricky part) many children, youth, and young adults with small to moderate amounts of hyperopia can see objects clearly at both distance and near. The reason for this is that they can use the focusing ability of the lens located in front of the eye to bring things into focus. They may, however, experience eye fatigue and/or headache with reading and near work. I like to to compare this situation to walking around with a thirty pound pack on your back: You can do it, but you may tire quickly. Young people with high amounts of hyperopia tend to experience blurred vision when viewing both distance and near objects. Further, the human eye loses its ability to focus with age, so middle-aged and older adults with hyperopia have difficulty seeing clearly at both distance and near ranges.
Hope that brings things into focus!
-Dr. Rachel Merriman