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Surgery for Presbyopia:

 

Even if you undergo LASIK or PRK as a young person and achieve perfect vision, you still will develop a condition called presbyopia typically beginning between the ages of 40 and 50. Presbyopia is the inability of the eye to focus at all distances, usually noticed when fine print starts to blur.


Some eye doctors disagree about what causes presbyopia. Most believe stiffening of the eye's lens contributes to the condition. Other theories suggest that presbyopia could also be related to continued growth of the lens or atrophy of the muscles controlling the lens.


In the past, the usual remedy was to wear reading glasses or special multifocal lenses (bifocal or progressive) for presbyopia. But in modern times, surgical remedies for presbyopia also are available for qualified candidates.


One of the first effective surgical options for presbyopia correction involved producing what is known as "monovision" during LASIK. But other surgical procedures such as conductive keratoplasty or CK (see below) also have been approved by the FDA, which gives eye surgeons additional options for correcting this common vision problem.


Several other experimental devices and procedures also are under investigation, but not yet FDA-approved. Here is a rundown.


Monovision and LASIK
One way eyecare professionals deal with presbyopia is by producing monovision. Normally, both your eyes work together equally when you look at an object, to produce what's called binocular vision. However, you probably have a dominant eye that your brain tends to favor for "sighting" (most right-handed people are right-eye dominant, for example). Contact lens fitters often take advantage of this "one-eye dominance" to produce monovision (think of it as the opposite of binocular vision) with the contacts: they fit one eye for distance vision (typically the dominant eye) and one for near vision.


Therefore, in monovision, one eye does more work (sighting) than the other. If one of your eyes is set for distance vision and the other is set for near vision, the distance eye will do most of the work when looking at objects in the distance, and the near vision eye will do most of the work when looking at objects close by.


Some LASIK surgeons will produce monovision in their presbyopic patients by purposely leaving the non-dominant eye slightly nearsighted so that these patients can see up close without glasses (out of one eye). Many are wary of the technique because not everyone can become accustomed to the absence of binocular vision. It's better to try monovision with contact lenses or trial lenses in the doctor's office first to be sure you can adapt.
Monovision LASIK initially was used off label, meaning that it had not received official FDA approval as an approach to correcting presbyopia. But in July 2007, the FDA announced approval of the Advanced Medical Optics (AMO) and Visx CustomVue excimer laser for performing the monovision procedure.


Monovision and Conductive Keratoplasty (CK)
Conductive keratoplasty uses low-level, controlled radio-frequency energy to shrink collagen found in the periphery of the cornea. This steepens the central cornea, in effect lengthening a too-short eyeball.


CK was FDA-approved in 2002 for the temporary reduction of farsightedness, then received approval in April 2004 for the temporary improvement of near vision in people with presbyopia.


This is another monovision technique: CK is used to help one eye see better up close, while the other eye is not touched. (If you are already nearsighted, that eye would wear a contact lens to see at distance.)


Again, it's a good idea to try monovision with contact lenses or a trial lens in the doctor's office before going ahead with CK, to make sure you'll adapt to it. After the three-minute procedure you'll likely notice improvement, but it can take a few weeks before you reach the final level of vision correction.


One attractive feature of CK is that it is minimally invasive. Some people experience tearing, foreign-body sensation, and/or vision fluctuation, but this is normally temporary.


Laser Thermal Keratoplasty (LTK)
In laser thermal keratoplasty, mild laser heat is used in a three-second procedure to shrink collagen in the periphery of the cornea to steepen the eye's surface for correction of near vision in farsightedness or presbyopia. Results are similar to those of CK (see above).


Surgical Reversal of Presbyopia (SRP)
with Scleral Expansion Bands (SEBs)

Here, the surgeon inserts four plastic segments made out of polymethyl methacrylate (PMMA) just below the surface of the sclera, which increases the distance between the muscles that focus the lens and the lens itself. Researchers think the extra distance augments the tension of the muscle, thus allowing it to do a better job of focusing the lens.


Results from early phase clinical trials involved five patients, all of whom were able to read newspaper print after scleral expansion bands were inserted. Modifications have been made to the earlier implants, and clinical trials as of 2006 were continuing. Overall, some eyes that have received the implants show improvement, and some do not.


Presbyopia Research: Do Tiny Bubbles Represent a Cure?
No vision correction surgery to-date has completely been able to address these focusing problems caused when the eye's natural lens grows rigid with aging.


But researchers at the University of Michigan in Ann Arbor reported in May 2006 that they have developed a novel new approach to correcting presbyopia, which involves using tiny bubbles to precisely guide laser beams as they restore flexibility and focusing ability to the eye's lens.


These tiny gas bubbles, known as microscale bubbles, first are created in the area of the eye's natural lens with laser pulses. Then high frequency sound waves (ultrasound) are used to push the bubbles against fibers making up the natural lens. Ultrasound helps track the movement and location of these bubbles to guide laser beams for precise placement of energy designed to loosen fibers and restore pliability to the lens. The technique has been perfected in pigs' eyes.
"Part of the sound is reflected, and from the characteristic of the reflection, you know where the bubble is," said Matthew O'Donnell, professor and chair of the University of Michigan Department of Biomedical Research. "It uses exactly the same technology as ultrasound imaging."


The team that created the technology has been in contact with several companies interested in commercial development, O'Donnell said.


Artificial Lenses (Refractive Lens Exchange or RLE)

One currently available option for presbyopia correction involves removing the eye's natural lens and inserting an artificial one in a procedure identical to cataract surgery. While this surgical procedure is not FDA-approved specifically for presbyopia correction, it may be available off label for qualified candidates. The surgical procedure, known as refractive lens exchange (RLE) or clear lens extraction, is becoming more popular because of the recent availability of three FDA-approved multifocal or accommodative artificial lenses capable of correcting presbyopia.


Multifocal LASIK (Presby LASIK)

Different zones in a multifocal artificial lens correct vision at near, intermediate, and far ranges. In an investigational procedure known as multifocal or presby LASIK, zones are established in a similar way on the eye's clear front surface (cornea) to correct presbyopia. Multifocal LASIK, also called presby LASIK, is an investigational procedure, which is not FDA-approved. U.S. clinical trials investigating the effectiveness and safety of the procedure currently are being conducted.


Corneal Inlays
Currently in FDA clinical trials, the ACI 7000 (AcuFocus and Bausch & Lomb) is a corneal inlay inserted just below your eye's surface to provide vision correction. This device corrects presbyopia by using principles similar to the aperture or opening through which light enters a camera - the smaller the aperture, the greater the range of what you see in focus.

 

 

 

 

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