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OPHTHALMOLOGISTS ENVISION BRIGHT FUTURE FOR AGING EYES

By Sean Henahan, Access Excellence

Presbyopia is the most common refractive error. There are now 590 million presbyopes in the world. By 2020, the figure will be 1 billion. Source: presbyopia.org

San Diego (July 22, 2001)- Ophthalmic surgeons, the ones who brought us intraocular lenses for cataract treatment and LASIK for improvement of visual acuity using a laser, are now setting their sights on presbyopia, the gradual loss of near vision that accompanies aging. Many of the options now being considered were discussed at the annual meeting of the American Society of Cataract and Refractive Surgeons here.

Presbyopia is the fancy medical term for aging eyes. Once a person passed the age of 45 years, the ability to accommodate, that is, see both at near (for reading) and far (for driving and everything else), begins to diminish. People tend to notice this first in the form of suddenly smaller text on the side of prescription bottles or assembly instructions for tools and toys.

In a majority of cases, a simple, inexpensive pair of reading glasses can take care of the problem. But even those who can overcome the 'vanity factor' soon grow tired of keeping track of their glasses and putting them on and removing throughout the day. This is where the ophthalmologists enter the picture.

 A PAGE FROM CATARACT TREATMENT

Another problem associated with again eyes is cataracts, in which the natural lens becomes cloudy, interfering with vision. Cataract patients now typically have their natural lenses removed and replaced with plastic lenses known as intraocular lenses (IOLs). The procedure is performed on an outpatient basis and is considered among the very safest of all surgeries. Patients regain clear vision, although they may need glasses for reading.

So why not use these implantable lenses to improve vision in otherwise healthy patients? Ophthalmologists initially resisted the idea of using these intraocular lenses to improve vision where cataracts were not present, citing the 'first, do no harm' precept of the Hippocratic oath. However, in recent years this resistance has melted away. One reason for this has been the arrival of a new kind of IOL known as the multifocal or accommodative IOL. Unlike older style IOLs, these new lenses offer the promise of restoring both near and far vision simultanesouly, that is, a life free from glasses.

One such lens is called the Array multifocal IOL. It is a plastic lens about the size of a contact lens, with concentric focusing rings included as part of the design. The device takes advantage of the brain's natural ability to adapt to near and far vision, as it uses the different elements of the Array lens depending on what it is looking at.

Howard Fine, MD, conducted a clinical study of the Array IOL in 36 patients with presbyopia. All of the patients ended up with vision of at least 20/40, that is, sufficient to pass the driver's test eye exam. A majority of patients reported improvements in near vision as well.

"These results suggest that, for carefully selected patients, clear lens replacement with the multifocal array lens offers a safe and effective treatment for presbyopia," said Dr. Fine, a clinical associate professor, Casey Eye Institute, Oregon Health Sciences University, and president of the American Society of Cataract and Refractive Surgery.

Dr. Fine emphasized the experimental nature of this work. Patients who receive this IOL for either cataracts or presbyopia may experience 'halos' at night time while driving and may notice an increased sensitivity to glare. Moreover, in many cases, patients may still require glasses for some tasks, he notes.

ACCOMMODATING VISION

The Array lens doesn't offer true accommodative vision, but rather fools the brain into seeing near and far. Another IOL however, called the CrystaLens does appear to offer the promise of true accommodation. That lens has a hinged design that allows the lens to move forward or back in response to the needs of the eye, mimicking the action of the natural lens.

Right: The Array IOL

Dr. Fine also reported the results of clinical study of the CrystaLens in which 30 patients had the IOL implanted. More than 90% of the patients achieved improvements in both enar and far vision with the lens, he reported.

"Our patients achieved excellent visual acuity, with striking improvements in accommodation. All of our patients had improvements in accommodation and function without glasses. The preponderance of patients with results of 20/40 or better tells us where this field is going. We are enormously enthusiastic about this lens. We anticipate that this is going to be a spectacular modality for addressing presbyopia.." he said.

A potential benefit of the CrystaLens compared with other IOLs is that it does not appear to create problems with glare or halos, he added. While the results with the CrystaLens look good in the short term, more follow-up is needed over a period of years to determine how the lens does over time, he noted.

Other implantable lenses are on the drawing boards for treatment of aging eyes. One lens now being studied at Vanderbilt University actually contains six different lenses which respond to action of the muscles of the eye to focus over the full range from near to far.

SURGICAL APPROACHES TO PREBYOPIA

IOLs are by no means the only option being considered for patients with aging eyes. Surgeons are also experimenting with a number of approaches that involve making incisions in the sclera (the white of the eye), often accompanied by the insertion of small pieces of plastic called scleral expansion bands.

Left: Scleral Bands in Place credit-Presbycorp

The idea is that expanding the sclera induces some anatomic changes that correct the process that creates presbyopia in the first place. These techniques are based on a controversial new theory that questions the mechanism by which the eye provides accommodative vision. Proponents believe that expanding the sclera just a small amount  increases the effective working distance of the ciliary muscle in eyes with presbyopia.

A number of researchers presented studies on the use of scleral expansion band surgery. While in many cases patients do appear to have some improvement in accommodative vision in the months following surgery, the effect regresses over time and patients are back where they started by about 12 to 24 months after the surgery, investigators reported.

LASER FOR PRESBYOPIA?

LASIK (LAser in SItu Keratomileusis) has become the most popular surgical method for improving vision. LASIK involves the use of an excimer laser to remove mere microns of tissue and reshape the center of the cornea. However, while the procedure has provided improved vision to celebrities and mere mortals alike, it has not been considered a treatment for presbyopia. This is because LASIK does nothing to alter the loss of accommodative vision that defines presbyopia.

This has not stopped laser surgeons from trying some new ideas. Some are using LASIK to create good near vision in one eye, and good far vision in the other, a result known as monovision. Other researchers are attempting to use the laser to create concentric focusing circles on the cornea, similar to the effect achieved with multifocal IOLs.

All of the approaches discussed in this article are still considered experimental. Most are in the midst of FDA clinical trials. The IOL studies are the most advanced, although other approaches can be expected to catch up soon.


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