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Presbyopia
by John W. Elman, OD
Presbyopia is an age related vision condition in which the crystalline lens of the eye has lost a significant amount of its flexibility, making it difficult for the presbyope to focus on close objects, even though distance vision is unaffected. Presbyopia is a natural part of the aging process of the eye. It is not a disease and it cannot be prevented.
Presbyopia may seem to occur suddenly, but the actual loss of flexibility takes place over a number of years. Presbyopia usually becomes noticeable in the early to mid-forties. See the section on this website titled How the eye focuses on near objects for a more detailed explanation of the loss of flexibity of the crystalline lens that occurs with aging.
Presbyopia may occur without any previous eye condtions, or it may occur in combination with preexisting conditions, such as astigmatism, myopia or hyperopia. The presbyope who previously had hyperopia (farsightedness), will continue to have hyperopia, but will find that more power is now needed in corrective lenses for near vision, as well as the power needed for distance vision, and that in addition to a problem with close vision, distance vision is also worse than it was. For those who were previously myopic, or nearsighted, presbyopia makes near vision worse while wearing the myopic distance corrective lenses, even though the younger myope previously could see clearly at all distances with corrective lenses. Occasionally myopic presbyopes experience better distance vision than previously, with a concurrent decrease in their myopic lens prescription power. Those with astigmatism continue to have that condition, but find that the lens power that worked for distance vision no longer works for near vision.
Treatment for presbyopia usually requires wearing glasses and/or contact lenses, which allow for a different focus for near and distance. The option may be reading glasses, which are removed for distance, or multifocal lenses, such as bifocals, trifocals, progressive additions and other options. These type lenses are divided into two or more sections and each section of the lens has a different power which focuses at different distances. When contact lenses are used the options include having contact lenses for distance and wearing reading glasses over them for close vision, bifocal or multifocal contact lenses, or monovision, where one eye is fit with a lens to focus close and the other eye is fit with a lens to focus for distance or modified combinations of lenses and modes of wear.
There are several new surgical procedures, utiliizing various artificial implanted lens devices which can also be used to correct presbyopia and restore near vision to those who have lost it do to the aging process. The surgical precedures all carry a certain amount of risk, and cost many times the amount of glasses or contact lenses. Even with these surgical procedures, glasses are sometimes needed for certain tasks, although many people having these procedures can do without glasses most of time. In all of the surgical procedures the organic crystalline lens of the eye is removed leaving most of the natural lens capsule intact. The lens capsule is a transparent bag or sac that envelops the natural organic crystalline lens. Only the front of the lens capsule is opened during implant surgery, and the lens capsule is used to hold the artificial intraocular lens implant(IOL).
The lens in the eye can be replaced with a plastic intra ocular lens implant (IOL) called the Crystalens™. (shown above). The center optical portion of the .Crystalens™. is smaller than the original natural crystalline lens it replaces, but the outer carrier or haptic portion of the implant is a flexible spring-like material, which is tucked into the peripheral edges of the lens capsule bag. Like a focusing camera that has a lens that moves back and forth to allow focusing at different distances, focusing ability is maintained in an eye with a Crystalens™. implant by the still active ciliary muscle, pulling and releasing tension on fibers(called zonules) at the periphery of the bag which displaces the artificial Crystalens™. forward within the eye when focusing on near objects. The Crystalens™. accomodates no greater than 1.00 or 1.75 dioptors, does not correct astigmatism, and while it generally gives good distance and intermediate vision, people find they still may need reading glasses for small close work. Another implant device is the Alcon AcrySof® ReSTOR® IOL , often referred to as the "ReStor" lens. It is placed in the lens capsule similar to traditional single vision IOLs, but the lens has concentric circular rings, which act as a diffraction grating to incorporate distance, intermediate and near focuses into the lenses. Other IOLs in this category are the Array and ReZoom™ lenses (made by Advance Medical Optics). The concentric ring design is able to bring more near focus into these lenses than the accomodating Crystalens™., The ReZoom design features an optimized multifocal surface (Balance View Optics) with five optical zones that optimize light distribution on the retina for varying lighting conditions and pupil sizes, but people sometimes find that their distance vision isn't as good because there may be glare at night caused by the rings. And of course the optical zone of the Crystalens™ is smaller than either the natural crystalline lens of the eye or the other multifocal IOLs, which could also cause glare problems at night, especially if the user has a larger pupil. Usually these surgical precedures are considered, along with the traditional single vision IOLs, when people have cataract surgery, when the crystalline lens of the eye has not only become hard because of presbyopia, but has also become clouded. Even in cataract surgery these multifocal devices are considered premium options by insurance companies and Medicare, and patients must pay a premium charge for these lenses, above and beyond insurance imbursements. When the surgical implants are done to correct presbyopia in someone without a cataract it is called a Clear Lens Extraction (CLE) and is considered to be entirely an elective procedure by medical insurance companies, who therefore pay nothing towards these procedures. A very good summary of options for presbyopia is contained on Dr. Wallace's LA Sight website.
Despite claims by various lens makers that youth can be restored and presbyopia can be vanquished by various multifocal corrective options, all treatments for presbyopia involve some compromise. Distance vision is not as good with a bifocal contact lens as it is with a single vision contact lens. Whenever a lens has multiple focuses there is less area of the lens available for any particular focusing distance than there is in dedicated single vision lenses (Single vision lenses are ones where the entire lens is made for a single focusing distance--for far distance focus only or for near focus only). The problems and limits of multifocal lenses are true whether we're talking about glasses, contact lenses, or intraocular lens implants. Although the Crystalens™. is probably the closest thing so far to bringing back lost presbyopic accomodation, its ability to do this is limited to less than 2.00 Diopters.
It is the job of the optometrist and opthalmologist who prescribe these devices to present the various presbyopic treatment options to each patient. Given this information, it is hoped that together patient and doctor can make the best choices, based on the patient's history and lifestyle.
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