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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. There are several refractive surgery solutions available to correct nearly all levels of nearsightedness.
Farsighted individuals have difficulty seeing at distance and at near, since the rays of light come to focus behind the retina. They 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. LASIK, Refractive Lens Exchange and Contact lenses are a few of the options available to correct farsightedness.
Asymmetric steepening of the cornea or natural lens causes light to be focused unevenly, which is the main optical problem in astigmatism. To individuals with uncorrected astigmatism, images may look blurry or shadowed. Astigmatism can accompany any form of refractive error and is very common.
Astigmatism can be corrected with glasses, contact lenses, corneal relaxing incisions, laser vision correction, and special intraocular lenses.
Presbyopia is a condition that typically becomes noticeable for most people after the age of 40. 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. Although presbyopia is not completely understood, it is thought that the lens and its supporting structures lose the ability to make the lens curvature greater during close vision effort. To compensate, affected individuals usually find that holding reading material further away makes the image clearer. Ultimately, aids such as reading glasses are typically needed by the mid-forties. Besides glasses, presbyopia can be dealt with in a number of ways. Options include: monovision and multifocal contact lenses, monovision laser vision correction, conductive keratoplasty (NearVision CK), new presbyopia correcting intraocular lenses, as well as the AcuFocus corneal inlay.
Presbyopia is a condition in which the ability to see up close in normal individuals, farsighted individuals, or individuals who have been nearsighted and undergone refractive eye surgery decreases as the age of 40 is approached. This physiological condition traditionally has required the use of reading glasses with plus lenses or bifocals in order to read. Presbyopia causes the near point, the closest point from your eyes at which you can see objects distinctly, to recede as we grow older.
When we are young our near vision is very good. A child ten years of age can hold small objects or print two inches from his eyes and be able to see clearly. By age 30 the same individual would have to hold objects or print at least six inches away to see it clearly. By the time 40 to 45 years of age occurs it is no longer possible to see objects closely or to read comfortably at 12 to 16 inches. By the early 40's most people began using reading glasses for such tasks such as sewing, hobbies requiring close vision, close work, and reading.
Farsighted individuals, who can see better at distance than at near without glasses, find that the loss of accommodation becomes apparent at even a younger age. This is because a farsighted person has to accommodate to see clearly at distance. When he tries to focus at near he has to throw in even more accommodation. Because farsighted individuals have a greater demand or need for accommodation, and the ability of the eye to accommodate decreases with age, we find that these individuals experience presbyopia at a much earlier age.
In contrast, nearsighted individuals can see better at near than at distance without glasses. These individuals can often wait longer before they need reading glasses. This is because the eye is normally in focus at near. However, if a nearsighted person wears glasses or contacts to correct their vision at distance then they will notice the loss of accommodation or presbyopia and often it begins for these individuals in their mid 40's. If there is enough nearsightedness or myopia then the nearsighted individuals may never need reading glasses because he can simply take off his glasses in order to read. However, such individuals must wear glasses at all times for distance tasks such as driving. Individuals who were nearsighted but underwent a refractive vision correction procedure will find their accommodative requirements would be the same as individuals who never wore glasses, because the eye has already been corrected for distance and the nearsightedness eliminated.
For those individuals who grew up wearing glasses, by the time they reach 40 not only will they need glasses for distance but often spectacles will be required for near vision. This is the reason that Benjamin Franklin invented bifocals in 1760. Bifocal lenses contain both a distance correction (on top) and a near correction (through the bottom). Therefore, it is possible with bifocals to see well at both near and distance by either looking through the bottom or top of the glasses. Other special types of glasses are often required for individuals who have to see at intermediate distances between near and distance. Such individuals may require trifocals, which have three segments in them depending upon the distance that one intends to look at. Such multipurpose eyeglasses have made it easier for many individuals by eliminating the need to constantly change glasses for different activities.
For over a 150 years the progressive decrease in accommodation with aging was thought to be a loss of lens flexibility often referred to as lens sclerosis. This theory was developed by the German scientist Helmholtz in 1855 and has been accepted as true until 1994. According to Helmholtz's theory, when an individual focused his eye for near his ciliary muscle in the eye contracted and released tension on the lens ligaments allowing the lens to thicken.
However, this theory was proved wrong in 1994 by an American scientist and ophthalmologist, Dr. Ronald Schachar who holds both a Ph.D. in physics and a doctor of medicine degree. Thanks to Dr. Schachar the errors in the Helmholtz theory were exposed and new applications found to reverse the loss of accommodation in the human eye. Dr. Schachar found that contrary to Helmholtz's theory there was no relaxation of the lens principal (equatorial) ligaments when accommodation occurred. Schachar showed that the equatorial fibers of the ciliary muscles pull directly on the ends of the lens and cause it to thicken, thus allowing one to see more closely.
In fact, Schachar also found that the aging lens does not lose its elasticity due to sclerosis. The ability to accommodate is inherent even in an older eye. The principal problem appeared to be the growth of the eye with time. The human lens is like a tree and lays down new layers as we age. Thus the lens lengthens approximately 20 microns per year as we age. By the time we reach the age of 40 the lens has increased sufficiently in size so that the ciliary muscles are no longer taut in the eye and can no longer exert tension through the equatorial fibers of the lens when the ciliary muscle contracts for accommodation. For this reason we lose our ability to accommodate at approximately the age of 40 and experience progressive loss of near vision as we get even older.