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| INTRAOCULAR REFRACTIVE SURGERY |
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Intraocular Procedures
Most candidates for intraocular refractive surgery have extreme myopia,
hyperopia, and/or significant presbyopia. For such patients, laser
ablation of corneal tissue may not be the best option. The risk of
corneal instability, dry eye, and bothersome visual side effects make
excimer therapy suboptimal for high refractive errors. Although
cornea-based procedures have dominated the refractive surgery market,
newer intraocular techniques are presenting options for select patients
seeking independence from glasses and contact lenses.
All intraocular procedures utilize implantation of an artificial lens
to ideally focus light. The practice of lens implantation was first
developed for cataract surgery. Lens implantation has multiple
potential advantages over corneal refractive procedures, including: 1)
accuracy for extreme refractive errors, 2) fewer visual side effects,
and 3) preservation of normal corneal architecture. Intraocular lenses
are now used in conjunction with the patient’s own natural lens (phakic
intraocular lens) or as a replacement for it.
Phakic Intraocular Lens
Anterior Chamber. The first intraocular lens (Verisyse™) for use
without removal of the crystalline lens gained FDA approval in
September 2004. The implant corrects 5 to 20 diopters of myopia by
affixing the rigid lens to the anterior iris. Results have been
excellent with 85% of participants seeing 20/40 or better (uncorrected)
at 6 months postoperatively. Patients retain the ability to
accommodate naturally, and some have demonstrated better corrected
vision than was possible preoperatively.
Posterior Chamber. Another phakic intraocular lens, the Visian ICL™
(Implantable Collamer Lens), is designed for placement behind the iris.
It is inserted with a folding technique that minimizes incision size
and potential astigmatism. FDA approval data for myopia between 3 and
20 diopters showed that at 3 years postoperatively 59% had 20/20 or
better, and 95% had 20/40 (uncorrected) acuities. Less than 1% lost
greater than or equal to 2 lines of best corrected visual acuity.
While phakic intraocular lens technologies have brought surgical vision
correction to patients with extreme refractive errors, some important
considerations deserve mention. The Verisyse™ requires a peripheral
corneal incision of at least 5 millimeters, which is closed with
sutures. The incision for the Visian ICL™ is approximately 3
millimeters and does not typically require sutures. Both phakic
intraocular lenses necessitate deep anterior chambers and peripheral
iridectomies to equalize pressure on both sides of the iris. The
complications that can occur with phakic intraocular lenses are similar
to those of other intraocular procedures (see below).
Refractive Lens Exchange
With the recent success of smaller incisions, high-frequency
ultrasound, and superior lens implants, cataract surgery itself has
become a refractive procedure. Some surgeons are now using the same
skills to offer refractive correction through lens removal with implant
placement prior to cataract formation. Refractive lens exchange has
been especially useful for higher levels of hyperopia. Multiple
options exist for the intraocular lens implant, which is selected after
careful patient interview, examination, and lens removal.
Monofocal Implant. The vast majority of implants today are monofocal,
which allow a clear image to be formed on the retina from a given
distance. Most patients choose to have an implant that will correct
for distance but will necessitate reading glasses for closer work.
Occasionally, monovision or planned myopia is used so that near and
intermediate distances are clear without glasses. Monovision may be an
option in motivated patients who are likely not to be bothered by a
mild decrease in depth perception.
Multifocal Implant. Certain implants contain concentric rings of
varying powers along the visual axis, thereby providing excellent near
and distance acuities. Newer designs (ReSTOR® and ReZoom™) may create
less halo side effect and contrast sensitivity loss, which have limited
the use of multifocal lenses in the past.
Accommodating Implant. The Crystalens™ is a silicone monofocal implant
with a flexible structure that is believed to allow a forward
accommodative motion. FDA approval data at one year postoperatively
demonstrated 92% of eyes were 20/25 or better for uncorrected distance,
and 89% could read 20/40 at near and intermediate without magnifying
spectacles. The implant has shown superb stability for all ranges of
vision in patients implanted at least 4 years earlier. Studies are
ongoing to verify its intraocular movement with near effort.
Risks of Intraocular Procedures
The complications of intraocular refractive procedures may be uncommon,
but their consequences can be devastating. Hemorrhage, infection,
retinal detachment, and persistent edema of the cornea or retina are
all possible with lens implantation procedures. Phakic intraocular
lens procedures carry the additional risk of cataract formation,
although this occurred in less than 5% of patients in the respective
FDA trials.
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