This condition occurs when the eyeball is too long from front to back or the cornea has too much curvature. Objects in the foreground are sharp, but distant objects appear out of focus.
This condition occurs when the eyeball is too short from front to back or the cornea has too little curvature. Objects in the distance are sharper than those in the foreground, but the entire visual field is somewhat out of focus.
Astigmatism occurs when the cornea is shaped more like an oval or the back part of a spoon than an even round bowl shape like a basketball. As a result, patients with astigmatism experience distortion or tilting of images because of unequal bending of light rays entering the eye.
Astigmatism is measured in diopters (a unit of measurement that represents the amount of correction needed in corrective lenses to normalize vision). Of all myopic people, 50% or more have astigmatism as well. Most of these people have corrections of less than 1 diopter. Patients with high degrees of astigmatism have blurred vision not only for distant objects as with myopia, but for near objects as well.
Presbyopia is the normal process of gradual loss of flexibility of the lens of the eye up close. It is the reason that reading glasses become necessary, typically in the mid-40`s, even for people who have excellent unaided distance vision. There is no cure for this loss of function. For some individuals, wearing a contact lens in one eye for distance and a contact lens in the other eye for reading, affords a reasonable solution. This is called monovision.