How eyes and prescription eyeglasses work!
It would be difficult to explain the function of just the lenses, so let’s start with the eyes.
The back of your eye is comprised of a multitude of cells that we call the retina. The retina reacts to light while the brain formulates the output from the retina into a picture. All this is like saying that you turn the key, and the car starts, but it’s important to recognize that there are a complex set of parts that operate together to let you see.
The lens, called the cornea, has to be smooth for perfect sight, if it’s not it causes what’s called an astigmatism. The lens also is flexible and able to change it’s curvature and thus the shape of it also affects our sight.
Lenses are designed to refract light, and if you’ve ever tried shining light through a prism you would see light being dispersed. Lenses for glasses work much in the same way. When light passes through glass or plastic it is focused towards the thickest point. Therefore if we use a lens that is convex, it will bring the object closer, or magnify (near sighted). The opposite would also be true, a concave lens would make objects look further (far sighted).
When we require glasses, we get an eye exam and a prescription, but how do we read this? A common measurement for lenses is diopters. A diopter is a measurement of the focal length in meters. So, 1 diopter is 1 meter. The number is derived by using the reciprocal of the focal length, in other words it is a fraction of 1 over the focal length in meters – 2 diopters would be .5 meters.
Regular optometrist eye exams ensure not only that you have the correct prescription for you, but also that your eyes are healthy.
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