LASIK options target special cases

The experience gained by their development could benefit every patient.

Special options for laser in situ keratomileusis (LASIK) could eventually result in every patient receiving a custom ablation instead of the “bull’s eye” patterns now available. And the technology used to correct hard-to-treat refractive errors such as irregular astigmatism, keratoconus or decentered surgeries could eventually benefit every patient.

Despite sophisticated lasers and microkeratomes, all that programmers can now do is instruct the laser how to ablate a cornea based on spectacle corrected vision, according to Stephen G. Slade, MD, of Houston, Texas.

“We hold up a lens, see how patients see out of that, and that is what we tell the laser to do,” Dr. Slade said. “It’s a sophisticated device, especially scanning lasers, yet all we are taking is a spectacle trial frame refraction. It’s the weak link. It’s the reason LASIK patients don’t see as well as gas permeable lens wearers, which is the goal — gas permeable vision of 30/15.”

Improving upon that involves finding all the information available to feed into the laser. Whether it involves corneal curvature, thickness, rate of change of curvature, the altitude maps, the prevailing belief is that topography is still in its infancy.

“We have very little information on how to do this,” Dr. Slade said. “There are lots of problems that come up. We know that when we do treatment for the patient’s eye, it affects regularity and refraction. We have to learn how irregularity will affect the patient’s refractive results.”

How each laser maker achieves this goal distinguishes each technology.

Two-step process

Visx (Santa Clara, Calif.) launched Contoured Ablation Pattern (CAP) internationally and started clinical trials domestically through Ralph Chu, MD, in practice in Maplewood, Minn.

CAP involves a software upgrade to the company’s Star S2 Excimer Laser System. It is designed to allow surgeons to treat irregular astigmatism, inferior corneal steepening, decentered ablations and central islands.

CAP allows a surgeon to specify the ablation pattern, depth, diameter and lo cation on the cornea, including off-center areas.

Dr. Chu said the program is a surgeon-controlled, topography-based treatment protocol for irregular corneas. Instead of being a topography-linked system, the package allows a physician to simulate ablation patterns that correlate directly with the laser software that they have. Surgeons can preplan their surgery on their topographer and implement it on the laser after finding the best pattern.

“It’s a two-step process,” Dr. Chu said. “The new software on the topographer is an exact simulation of what the laser software is. You can simulate exactly what you are doing with the topographer and type in that exact protocol into the laser.”

Dr. Chu has not started the clinical trials yet, but expects quick approval because the technology used Food and Drug Administration-approved devices.

Ronald R. Krueger, MD, medical director of refractive surgery at the Cleveland Clinic Foundation in Cleveland, said the resolution of the ablation remains a key issue.

“Visx is breaking up their view of the cornea into certain segments. SmoothScan then adjusts to treat more in one segment than the other. The real accuracy of resolution comes from how small you can make a spot,” he said.

Autonomous (Orlando, Fla.) has a small diameter beam and Summit’s (Waltham, Mass.) disk technology can be adjusted very specifically for its broad beam system, Dr. Krueger said. The SmoothScan has a 2 mm to 3 mm beam, which limits the resolution.

Custom corneas

Summit Technology uses an ablatable disk for its Apex Plus laser, so now the company is working with international physicians to customize disks and treat patients with significant corneal irregularities such as asymmetric astigmatism and decentered ablations.

According to Dr. Krueger, the company’s goal is to use topography data to design an ablatable disk for the eye. The broad beam system would then create a customized ablation pattern when used.

Also, Summit’s acquisition of Autonomous grants them access to that company’s CustomCornea Measurement Device (CCMD). That technology characterizes certain ocular conditions such as myopia, astigmatism or hyperopia by defining its wave front pattern. The wave front pattern is translated into a 3-D format and then coupled to the laser for custom corneal ablation.

“The wave front information is precise and subtle,” Dr. Krueger said. “Little fluctuations in the wave front will make little variations in the firing pattern.”

The company has demonstrated a simulated treatment pattern in patients but has not started clinical trials.

According to Jonathan Frantz, MD, of Ft. Myers, Fla., CustomCornea has potential, because the entire visual system needs consideration before surgeons can push beyond correcting simple refractive problems.

“We want to treat the optical system and not the cornea,” he said. “You can have the most perfect corneal topography in the world but the patient won’t see well. We don’t want a homogenous topography; we want a perfect wave front so that we are able to get people the best possible vision.”

Wave front technology assesses every ray of light that enters the eye and then determines what changes will produce the clearest image, even if it involves a nonspherical ablation pattern.

Autonomous Technologies has worked with the CCMD under an investigational device exemption at Dr. Frantz’s offices. CCMD measures the wave front pattern returning from a laser spot on the retina and creates a 3-D map of aberrations. It then figures out what changes are needed to correct all the aberrations.

In this scenario, every patient is a special case.

“You will generate an algorithm and ablation pattern for every person,” he said. “That will involve more than just spherical correction. It will involve treating aberrations in the patients’ optical system. This technology has the potential to drive results to another level.”

He started the clinical work over the summer and said he intends to present the first results at the International Society of Refractive Surgery’s Summer World Refractive Surgery Symposium this year and a workshop at the Eighth Annual Ocular Surgery News Symposium on Cataract, Glaucoma and Refractive Surgery.

Linking systems

Dr. Slade switched over to Orbscan with Technolas (Bausch & Lomb Surgical, Claremont, Calif.), and has started to do ablations with topography and altitude maps.

He and other researchers have operated on 200 eyes with the Technolas laser. In general, one-third of patients improved significantly, and another one-third had experienced subjective improvement. The remaining one-third of patients had some form of refractive improvement but did not report a subjective improvement in vision.

Researchers are now working on linking the Technolas laser to the Orbscan software system.

“The beauty of topography-linked computer ablations is that the computer can learn from previous operations and adjust future techniques,” Dr. Slade said.

LaserSight (Winter Park, Fla.) also has entered research and development on linking topography to custom ablations, but has only just begun. Michael Dayton, chief technical officer and senior vice president of LaserSight, declined to enter into a detailed interview to discuss the company’s plans.

“We believe that with a small flying random scanning device, we expect that our scanning laser platform will be effective at treating and creating a truly custom ablation for that specific cornea,” he said.

He added that physicians are using its small-diameter beam scanning technology overseas to correct prior corneal surgery or keratoconus, for example. The company expects to soon begin its domestic LASIK trials with its LSX excimer laser. The LSX excimer laser is expected to receive domestic PRK approval in the second half of 1999.

Who benefits most?

Initially, custom LASIK options are targeted to a limited range of patients with special needs. As surgeons learn more about the application, they may be able to apply it to more people.

According to Dr. Frantz, the advances in technology mean that every patient can be treated as a special case. The new technology will generate a new algorithm and ablation pattern for every person, and each pattern will adjust to more than just spherical correction or optical irregularities.

Dr. Krueger said the new technology becomes a tremendous resource to correct prior patients with less than optimal outcomes.

“With most customized treatments, you will want to apply this technology to patients who are hurting in terms of best corrected visual acuity,” he said. “If you deal with a normal eye that doesn’t see that badly but has subtle irregularities, it is probably not a good idea to use a topography-guided ablation, but a wave front-guided ablation.”

Although researchers have designed the advanced technology to help the extreme cases, the greatest benefit of the technology will be for the uncomplicated cases with naturally occuring higher order aberrations.

“No one has a bull’s eye circular topography preoperatively,” Dr. Slade said. “We all have some irregularities. With regular LASIK, we are taking a spectacle refraction and that’s the information we’re giving the laser. It’s very little information.”

For Your Information:

• Stephen G. Slade, MD, practices at 3900 Essex, Ste. 101, Houston, TX 77027; (713) 626-5544; fax: (713) 626-7744. Dr. Slade has no direct finanical interest in any of the products mentioned in this article. He is paid per course by Bausch & Lomb to teach courses.
• Ronald R. Krueger, MD, practices at The Cleveland Clinic Foundation, 9500 Euclid Ave., Ste. A31, Cleveland, OH 44195; (216) 444-8158; fax: (216) 445-8475. Dr, Krueger has a direct financial interest in Summit. He is not a paid consultant for any companies mentioned.
• Jonathan Frantz, MD, practices at Florida Eye Health, 12731 New Brittany Blvd., Fort Myers, FL 33907-3632; (941) 418-0999; fax: (941) 418-0091. Dr. Frantz has no direct financial interest in any of the products mentioned in this article. He is a paid consultant for Autonomous Technology.
• Michael Dayton can be reached at 3300 University Blvd., Ste. 140, Winter Park, FL 32792; (407) 678-9900, ext. 118; fax: (407) 678-9981. Mr. Dayton is chief technical officer and senior vice president of LaserSight Technologies.
• Ralph Chu, MD, practices at 1965-11th Ave. E, Ste. 102, Maplewood, MN 55109; (651) 773-8857; fax: (651) 773-5985. Dr. Chu has no direct financial interest in any of the products mentioned in this article, nor is he a paid consultant for any companies mentioned.