الفهرس 
Multifactorial TheoryOnly 14 pages are availabe for public view
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Abstract
Presbyopia is a problem attributed to age-related loss of accommodation, resulting in the need to utilize reading glasses or bifocals for near work. A person unable to maintain 3 D of accommodation for any length of time is considered to have symptoms of presbyopia (Atchison, 1995).
In this study we try to discuss the different procedures developed for correction of presbyopia:
Eye glasses: lens options for presbyopes include Reading, Bifocal, Tri-focal and Progressive addition glasses. They are the most common methods of correction for presbyopia. Reading glasses are typically worn just during close work. Multifocal means points of focus: the main part of the spectacle lens contains a prescription for nearsightedness or farsightedness, while the other portion of the lens holds the stronger near prescription for close work. Progressive addition lenses are similar to multifocal lenses, but they offer a more gradual visual transition between the two prescriptions, with no visible lines between them (Patorgis, 1987)..
Contact lenses: in addition to glasses, CLs have also been found to be useful in the treatment of presbyopia. There are many options for correction of presbyopia using the CL including Reading glasses with single vision CL, Bivision, Modified Bivision, Multifocal, Monovision and Modified Monovision CL (Gauthier et al, 1992).
LASIK monovision: a promising alternative treatment for presbyopia is correction of one eye for distance and the other eye for near. However, the indications, success rate and limitations of monovision remain unclear. Inspite of its limitations, monovision is effective for correcting presbyopia in some patients (Cumming, 2002).
PresbyLASIK: a procedure that involves constructing a flap and precisely forming an annular ablation in a centralized region of the newly exposed corneal stroma. This technique produces an un-ablated central protrusion of the stroma and transforms the exterior surface of the flap into a multifocal surface that effectively provides good distance and near visual acuity. The preliminary results are encouraging; however, it depends on near/ far dominance and the pupil size and there is a considerable risk of scatter, halos, ghosting and reduced far visual acuity (Anschutz, 1994).
Conductive Kertoplasty: a non-ablative and non-incisional procedure that does not require creation of a flap and uses radiofrequency energy to steepen the central cornea. The FDA has recently granted approval of conductive kertoplasty for the temporary reduction of mild to moderate (+0.75 to +3.0 D) previously untreated spherical hyperopia in patients aged 40 or older. Accordingly, presbyopia can be corrected by the creation of monovision. Conductive keratoplasty for the treatment of presbyopia provided safe, effective, predictable, and stable results (Jason, 2007).
Scleral expansion bands: this procedure depends on the Schachar theory of presbyopia. It involves placing 4 PMMA bands through a scleral tunnels initiated 2 mm posterior to the limbus to allow expansion of the sclera over the area of ciliary body giving a space to the zonules to act upon the lens. It is a low risk and minimally invasive procedure with mild postoperative complications. SEB appear to increase the amplitude of accommodation between 4 and 6 diopters (Ellis, 2000).
Anterior Ciliary Sclerotomy: it also depends on the Schachar theory of presbyopia. It entails performing scleral radial incisions over the ciliary body area in specific quadrants to expand the sclera and thus giving the ciliary body more room. The mean amplitude of accommodation postoperatively was 1.7 D; however, rapid regression to preoperative accommodation amplitude has been observed (Fukasaku, 2002).
The Anterior Chamber bifocal IOL (NEWLIFE): it is a phakic anterior chamber, angle supported IOL. It allows the patients to perceive images at several focus distances without relying on ciliary body function and capsular mechanics. The main advantage of its implantation in the surgical correction of presbyopia is that it is a reversible process (Perez et al., 2000).
The Posterior chamber multifocal IOLs: they have two types: the refractive (like the AmoArray and the ReZoom) and the diffractive (like the AcrySof ReSTOR). They are zonal progressive IOLs that provide a progressive power distribution. They can provide better useful near vision while maintaining a good distance vision and high levels of subjective patient satisfaction compared with monofocal IOL. They result in some loss of contrast sensitivity (Packer et al, 2003).
The Accommodating IOLs: (like the CrystaLens and the 1Cu Accommodative IOL) they depend on the movement of the lens in a backward and forward motion along the axis of the eye in response to pressure changes of the eye that result from relaxation and contraction of the ciliary muscles and the pressure of the vitreous (Probst, 2002).
Refilling the lens capsule with inflatable endocapsular ballon: it is an investigational technique trying to maintain the ocular accommodation by refilling the lens with inflatable endocapsular ballon following endocapsular phacoemulsification. This procedure is somewhat technically difficult and the outcomes are not encouraging (Nishi et al., 1993).
Lens refilling with injectable silicone: it has the same idea as the endocapsular ballon but using a silicone plug for sealing the capsular opening after direct lens refilling with a silicone mixture without using ballons. It is a feasible technique but results are also disappointing (Nishi and Nishi, 1998).
Future considerations: many procedure rise in order to correct presbyopia, like the Futurestic lenses for refractive lens exchange as the smart IOL, the light adjustable lens, the FlexOptic IOL, the FluidVision IOL, the TetraFlex IOL and the NuLens IOL (Ben-Nun and Alio, 2005); besides the application of the visiodynamis theory: “LaserACE’’ (Hipsley, 2007).