Surgical
The Evolution Of Refractive Eye Surgery
About 120 million people in the United States wear glasses or contact lenses to correct myopia, hyperopia, or astigmatism according to the National Eye Institute. In recent years, there has been a growing interest in refractive eye surgeries, mainly LASIK (laser in situ keratomileusis).
RK (Radial Keratotomy)
First performed in the 1940s in Japan, this process was improved upon in the 1960s in the former U.S.S.R, and was introduced in the United States in the late 1970s. By the early 1990s, Chiron Vision, now part of Bausch & Lomb, helped elevate RK from the fringe to the mainstream by standardizing the procedure, actively promoting it, and creating instruments specifically designed for RK. These improvements in RK surgical technology made it an increasingly common procedure. The National Eye Institute reported in 1995 that about 250,000 RK procedures were done each year, up from 30,000 in 1990.
During the RK procedure, the surgeon makes a series of cuts in a spoke-shaped pattern around the pupil, penetrating 85-95 percent of the depth of the cornea. The incisions cause the perimeter of the cornea to bulge out, flattening the center. The degree of bulge, and therefore the amount of vision correction, is determined largely by the number and length of the incisions.
ALK (Automated Lameillar Keratoplasty)
As RK evolved, surgical techniques expanded to include ALK, a process that involves performing the actual correction underneath the surface of the cornea.
Using a microkeratome, the surgeon cuts into the cornea to create a hinged flap that is folded to the side. To correct myopia, the surgeon flattens the cornea by using the microkeratome to remove a thin disc of tissue centrally from the exposed surface of the cornea. The flap is then replaced without the need for sutures.
Procedure Advancements
Lasers were being tested as viable surgical options throughout the 1970s and 1980s, and the use of excimer lasers for PRK (Photorefractive Keratotomy) to correct myopia was approved by the FDA in 1995. Since then, laser technology has continued to evolve and computer-controlled laser procedures have become the preferred choice for vision correction among surgeons and patients.
PRK (Photorefractive Keratotomy)
The laser removes a microscopic amount of tissue from the cornea's surface to reshape the cornea.
LASIK (Laser in-situ Keratomileusis)
This process is similar to ALK, but involves an excimer laser for the actual visual correction. Using a microkeratome, such as the Bausch & Lomb Zyoptix® XP microkeratome, the surgeon cuts into the cornea to create a hinged flap. With the flap folded to the side, the laser is used to remove tissue and reshape the cornea. The flap is replaced at the end of the surgery. With LASIK, the patient has less discomfort and faster healing time than with PRK.
Laser Advancements
Broad Beam
First- and
second-generation excimer lasers use a broad beam (about 6 mm in diameter) with
an aperture that controls the amount of the beam that is exposed to the eye
during any single pulse.
Flying Spot
The newest generation excimer lasers, such as Bausch & Lomb's Technolas® 217A, utilize an
innovative technology called a "flying spot laser" for true scanning. A
narrow beam (about 2 mm wide) contacts the eye at lightning speed in a pattern
that allows the eye to clear in one place before contacting that area again.
The laser beam covers a broad surface area, but does not penetrate as deep as
in RK procedures. The beam is pulsed in tiny, non-overlapping spots all over
the treatment zone, following a pattern controlled by the laser's computer.
Unlike the broad beam, the full width of the flying spot beam is placed on the
cornea during every pulse. The flying spot technology is designed to produce a
smooth corneal shape and increases the accuracy of the surgery.
The newest generation excimer laser, the Technolas® 217z
Zyoptix System for Personalized Laser Vision Correction, combines both a
2mm and a 1mm beam.
