Long vs. Short Eyes

I am often asked in clinic about what causes the need for glasses. The basic answer is that light entering the eye does not get focused appropriately on the retina in the back of the eye. This is why adding a lens (like glasses or a contact lens) can help to appropriately focus that light. There are a few different ways to think about this, but one way is to think of the focusing parts of the eye (which are the cornea and the lens in the front of the eye) as stable/fixed. If that is the case, one could say that the eye has to be just the right length (from front to back) for the retina to be placed where the light comes into focus. If the eye is too long or too short, the point at which light is focused will not be on the retina, which will cause a blurred image. One last point about this model is that eyes that are too long will be “near-sighted” (myopic) and that eyes that are too short will be “far-sighted” (hyperopic).