Myopes considering refractive surgery are advised that surgically correcting their nearsightedness may be a disadvantage after age forty, when the eyes become presbyopic and lose their ability to accommodate or change focus, because they will then need to use glasses for reading. Myopes with low astigmatism find near vision better, though not perfect, without glasses or contact lenses when presbyopia sets in, but the more astigmatism, the poorer the uncorrected near vision.A surgical technique offered is to create a "reading eye" and a "distance vision eye", a technique commonly used in contact lens practice, known as monovision. Monovision can be created with contact lenses, so candidates for this procedure can determine if they are prepared to have their corneas reshaped by surgery to cause this effect permanently. Mechanism
The cause of presbyopia is lens hardening by decreasing levels of α-crystallin, a process which may be sped up by higher temperatures. It results in a near point greater than 25 cm (or equivalently, less than 4 diopters). In optics, the closest point at which an object can be brought into focus by the eye is called the eyes near point. A standard near point distance of 25 cm is typically assumed in the design of optical instruments, and in characterizing optical devices such as magnifying glasses.There is some confusion over how the focusing mechanism of the eye works. In the 1977 book, Eye and Brain, for example, the lens is said to be suspended by a membrane, the zonula, which holds it under tension.
Eye drops intended to restore lens elasticity are also being investigated. Etymology
The term is from Greek πρέσβυς presbys meaning "old" and ὤψ ōps meaning "sight" (GEN ὠπός ōpos). History
The condition was mentioned as early as the writings of Aristotle in the 4th century BC. Glass lenses first came into use for the problem in the late 13th century. See also
Vuity

References
External links

"Presbyopia" at MedLinePlus Medical Encyclopedia