Nearsighted individuals typically have problems seeing well at a distance and are forced to wear glasses or contact lenses. The nearsighted eye is usually longer than a normal eye, and its cornea may also be steeper. Therefore, when light passes through the cornea and lens, it is focused in front of the retina. This will make distant images appear blurred.
Farsighted individuals typically develop problems reading up close before the age of 40. The farsighted eye is usually slightly shorter than a normal eye and may have a flatter cornea. Thus, the light of distant objects focuses behind the retina unless the natural lens can compensate fully. Near objects require even greater focusing power to be seen clearly and therefore, blur more easily.
Asymmetric steepening of the cornea or natural lens causes light to be focused unevenly, which is the main optical problem in astigmatism. Most patients have heard this referred to as “football-shaped” corneas. To individuals with uncorrected astigmatism, images may look blurry or shadowed. Astigmatism can accompany any form of refractive error and is very common.
Presbyopia is a condition that typically becomes noticeable for most people around age 45. In children and young adults, the lens inside the eye can easily focus on distant and near objects. With age, the lens loses its ability to focus adequately.
To compensate, affected individuals usually find that holding reading material further away makes the image clearer. Ultimately, arms are no longer long enough and aids such as reading glasses are typically needed by the mid-forties.