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