It may sound like Greek, but the words myopia, hyperopia, astigmatism, and presbyopia describe vision problems that afflict countless millions of people of all ages.
Refraction refers to the ability of the eye to focus light.
The shape of the cornea, the strength of the lens and of the eye, and the length of the eyeball determine how clearly you see. If even one of these factors is not coordinating properly with the others, light will not focus correctly and your vision will not be clear. People with myopia can see objects closer to them, but have difficulty focusing on distant objects. The condition is caused by a cornea that has more curvature than normal, or an eyeball that is too long. In either case, light is focused at a point in front of the retina, causing a blurred image.