Innovations | Sep 2005
The 193-nm Wavelength and Beyond
Refractive surgeons consider how the refractive industry will progress.
William I. Bond, MD, ACS; Stephen Coleman, MD; Sheraz Daya, MD, FACP, FACS, FRSC(ED); W. Bruce Jackson, MD, FRCSC; George Mintsioulis, MD, FRCSC; Guy M. Kezirian, MD, FACS; Robert K. Maloney, MD; Louis E. Probst, MD; and John A. Vukich, MD
WILLIAM I. BOND, MD, FACS
To see where we will go, we first need to look at where we have been. Unlike most medical specialties, corneal refractive surgery is, or can be, rapid, superficial, largely mechanical, and only lucrative when done efficiently, all of which can make the OR akin to an assembly line. Success tends to be measured solely in terms of volume. Reports of trouble or complications are halfhearted, grudging, slow, and incomplete.
GATHERING INFORMATION
Reliable knowledge, amazingly, is much more likely to come from trusted friends and colleagues than from published medical information. Corneal refractive surgery will continue to be not only a medical specialty, but a retail business as well.
Endless debate about the refinements needed to produce an ideal (although unavoidably subjective and thus perhaps unknowable) endpoint has characterized refractive surgery for the last several years. This debate is rooted in, and confused by, competing commercial interests. The willingness of some refractive surgeons to conspire against other refractive surgeons has been a deplorable side effect. The pervasiveness of commercial interests in our discussions and theorizing make predictions about what will be in the best interest of the patient even more difficult.
FUTURE IMPROVEMENTS
Who knew LASIK would be as good as it is? Our cavils about how to improve it in small ways are insignificant compared with the fact that it works so well.
Surface treatment will fully come into its own only with the adequate control of pain and variable healing responses between patients. Intraocular procedures will not replace corneal procedures for the great majority of straightforward refractive errors. The former are inherently slower and more demanding in time and resources (such as sterile ORs) than the latter. Furthermore, the inevitable complications are far more devastating with intraocular procedures than with corneal procedures.
STEPHEN COLEMAN, MD
The 193-nm wavelength has long been used to etch a variety of surfaces in the industrial setting. It is ideally suited for the cornea, primarily because it causes less collateral thermal damage than its UV counterparts, namely 248-nm (Krypton fluoride), 308-nm (Xenon chloride), and 351-nm (Xenon fluoride).1 Its robustness and dependability, perhaps unknown traits in 1983, when Stephen Trokel, MD, first appreciated the elegant predictability of the excimer's ablation profile, are fundamental reasons why this wavelength is used on such a widespread basis today.
LIMITATION
The wavelength's primary shortcoming is its need for gases that must be purchased and replaced on a routine basis. Efforts to eliminate this requirement, such as with solid-state lasers that modify an infrared wavelength to UV, have largely been unsuccessful.
REGISTRATION
The 193-nm platform is here to stay and will drive LASIK, and thereby the entire refractive surgery market, into the foreseeable future. Modifications will improve, not replace, this technology. For instance, iris registration, recently approved by the FDA for the Visx laser (Visx, Incorporated, Santa Clara, CA), uses landmarks on the iris that are unraveled, identified, compared, and then matched to an image captured at a wavefront sensor.
Because all wavefront-guided corrections are centered on the pupil, iris registration is a significant advance toward the goal of accurately placing the ablation profile on the cornea. The software compensates for centroid shifts as the pupillary size varies during the course of a procedure. As a clinical investigator for Visx, Incorporated, and with my practice being a beta site for this particular technology, my sense is that it will be roundly accepted and swiftly integrated into all LASIK procedures, similar to the way in which tracking systems for the x, y, and z axes were adopted.
ABLATIONS
Truly intriguing is the concept of intrastromal ablations being developed by Intralase Corp. (Irvine, CA). Like a YAG, the 1053-nm Intralase laser works by a process known as laser-induced optical breakdown, whereby hot plasma expands and cools, resulting in cavitations. Having had the pleasure of using this femtosecond laser during the past year, it would not surprise me if this impressive company adds this application, perhaps first aimed at low hyperopes or plano presbyopes similar to conductive keratoplasty (CK; Refractec, Inc., Irvine, CA), sooner than many think. This technology would complement Intralase's already ambitious efforts in the therapeutic arena, specifically with respect to posterior lamellar and partial-thickness keratoplasties.
SHERAZ DAYA, MD, FACP, FACS, FRCS(Ed)
The 193-nm wavelength has been commercially used for more than 1 decade in the US but more than 17 years in Europe and other parts of the world. The technology has progressed dramatically in a relatively short time from using single-zone, to multizone, to flying-spot lasers. Coupled with better measurements of optical systems, customized treatments to varying degrees are a reality. Additionally, we have transitioned from PRK to LASIK, back to some form of surface ablation, and then to LASIK with the introduction of the Intralase only a few years ago.
The main thrust for the next few years will be to improve the efficiency and reliability of diagnostics so that all laser vision correction will be customized. Lasers also will become faster and more accurate as eye trackers also improve and become able to actively track torsion as well as the x, y, and z axes.
Economics
The manufacturers of lasers as a whole are leaning toward a per-procedure fee, and this appears to be the only sensible business model for maintaining a refractive arm in their business. Although the US is accustomed to this issue from the Pillar Point days (when royalties were paid on each procedure and the concept of prepaid cards evolved), the rest of the world is having a difficult time reconciling the need to pay per case. Physicians will have to adjust their business models, ultimately by increasing the procedure's price and maintaining a higher cost to patients. This adjustment is probably well worthwhile to the consumer for a more reliable and effective procedure.
The Future of the 193-NM Wavelength
Will the 193-nm laser survive in the long term? Probably, but there are solid-state lasers that, with further improvements, may provide a competitive edge in the future. Overall, the 193-nm wavelength laser has revolutionized the practice of refractive surgery. I am sure many refractive colleagues join me in celebrating its continued development and success.
W. BRUCE JACKSON, MD, FRCSC, AND
GEORGE MINTSIOULIS, MD, FRCSC
Since we started performing excimer laser surgery at the University of Ottawa Eye Institute 12 years ago, dramatic improvements in lasers' hardware and software have increased our expectations and those of our patients. With the current generation of lasers, we expect 20/20 or better vision with one or more lines of vision gained, compared with spectacles or contact lenses. Yet, we are continually amazed that patients we treated in 1993 still see 20/25 and have nothing but praise for their results and the impact surgery has had on their lives.
MODIFICATIONS
The biggest changes laser vision correction has undergone include the evolution from broad-beam to flying-spot lasers, faster and smoother ablations, and the introduction of pupil and cyclotorsional tracking. Also, enlarged optical zones with transitions out to 8-mm diameters or larger have had the greatest impact by almost eliminating the optical symptoms of glare, ghosting, and halos, especially at night. Wavefront-guided ablations have refined the treatment of lower-order aberrations (sphere and cylinder) and permitted us to address higher-order aberrations. Modifications to the software have allowed for more prolate corneas.
Future programs will take into account corneal-height data to enhance results. Multifocal corneal ablations now provide pseudoaccommodation, which, in many cases, frees presbyopic patients from their spectacles. In the future, adaptive optics will allow patients to preview their postoperative results at the aberrometer and choose the type of correction that is best for them. Some may want to retain some higher-order aberrations for greater depth of field, whereas others may chose the sharpest distance vision with minimal optical aberrations. Finally, an integration of corneal topography and wavefront technology will yield more precise therapeutic and retreatment laser corrections.
We look forward to new lasers' having a smaller footprint and ultimately being solid state. Innovative lasers will have active tracking in all axes and be able to confirm a patient's identity and prescription by iris recognition. The addition of real-time pachymetry and the ability to monitor the amount of tissue removed per pulse will allow more consistent and precise ablations despite environmental variables such as room and tissue hydration. Additionally, surgeons will be able to ablate through scars. Faster ablations will decrease the time a patient lies under the laser, thus minimizing environmental variables. New modalities to control wound healing will increase the popularity of surface ablation by making epithelial healing faster, more predictable, and less uncomfortable.
GUY M. KEZIRIAN, MD, FACS
Corneal resurfacing procedures with excimer lasers use the 193-nm wavelength for several practical reasons. Corneal absorption at this wavelength is optimal because small amounts of energy efficiently remove tissue, the spread of energy to surrounding areas is minimal, and the wavelength appears to be safe and without teratogenic effects. In addition, the ablations can be exquisitely localized to allow for submicron sculpting. This shaping allows us to design very precise ablation profiles to correct most refractive errors. At least for the next few years, the 193-nm wavelength is here to stay.
The forces that will drive future innovation are quality and economics. Several issues come under the heading of quality—better optics, better predictability, and safer treatments. Economics will limit the rate at which changes are adopted and will force new technologies to be efficient.
OPTICS
Corneal-based procedures will be limited to the treatment of low and moderate degrees of refractive error due to the better optics that intraocular procedures can provide. The optical quality of corneal-based refractive surgery is limited by the amount of corneal tissue available. Induced spherical aberration following corneal-based procedures is a well-recognized problem. Newer lasers attempt to minimize spherical aberration by preserving the basic corneal shape, but at the cost of more tissue. Because available corneal tissue is restricted, the limit for spherical aberration-neutral procedures using a 6.5-mm optical zone is approximately 6.00D. This amount is not a function of the lasers but of the cornea.
Surgeons will demand that all excimer laser companies improve their ablation profiles to minimize induced spherical aberrations, and they will look to procedures not based on the cornea such as phakic implants for corrections beyond 6.00 to 8.00D. In addition, surgeons will insist on improved profiles for hyperopia and myopia.
The optics of corneal-based corrections are also limited by the location of the cornea anterior to the nodal point. The best refractive corrections are performed at the nodal point using IOLs. This issue mostly affects higher corrections and is another reason why excimer-based procedures will be reserved for lower corrections.
IMPROVED PREDICTABILITY
Better predictability will come in the form of faster treatments that decrease the tissue's dehydration, better ablation profiles, more sophisticated nomograms, and real-time monitoring of the laser's performance. Faster lasers also mean spot sizes can be decreased without extending the treatment times. Greater speed will improve the precision of the ablation profiles and the smoothness of the ablated surface. It will also allow the surgeon to preset the final asphericity for each quadrant of the cornea to optimize vision. More sophisticated nomograms will permit surgeons to control aberrations as well as the refractive outcome. Real-time monitoring of the laser's performance will enable the remote servicing of lasers and will ensure that a malfunction is detected as soon as a problem develops.
These changes will all have financial implications. Some innovations may not be viable. Others, such as the reduction of spherical aberration in all treatments, will allow surgeons to bypass customized treatments for most eyes and avoid the added time and expense they entail.
ROBERT K. MALONEY, MD
As Yogi Berra said, “It's hard to make predictions, especially about the future.” Corneal refractive surgery has had an extraordinary run of success. How much better can it get? The accuracy of corneal refractive surgery is fundamentally limited by the epithelium, which remodels in response to a wound. Control of epithelial remodeling seems remote at present. As a result, corneal refractive surgery always will have some inherent inaccuracy. The future of this modality will require an implant or other treatment that may be adjusted without additional surgery to refine the refractive effect postoperatively. Early attempts at this type of procedure using a femtosecond laser to cause local stromal collapse have so far been unsuccessful.
LIGHT-ADJUSTABLE ONLAY
Calhoun Vision, Inc. (Pasadena, CA), is developing a light-adjustable corneal onlay. The onlay is made of bioengineered artificial protein consisting of elastin and fibronectin, the latter of which promotes epithelial migration and adhesion. Physicians choose the appropriate power for the implant in the same way they select a contact lens. After removing the epithelium, the surgeon attaches the onlay with a biochemical adhesive. The epithelium then heals over the onlay in a few days, much as it would after a PRK procedure. To adjust the refractive correction postoperatively, the surgeon uses a UV light source to reshape the onlay without disturbing the epithelium. Voilà! Perfect vision. Should there be any problems, the onlay may be removed, restoring the cornea to its preoperative condition. Calhoun has already used light-adjustable technology to adjust the power of an IOL in the eye after cataract surgery. According to a conversation with Daniel Schwartz, MD (August 2005), in research conducted by Arturo Chayet, MD, 16 consecutive light-adjustable IOLs have been fine-tuned to within 0.25D of the intended spherical refraction.
Refractive surgery is approaching a fork in the road. Do we continue to perform corneal refractive surgery, or do we move to phakic IOLs and lenticular refractive surgery? Light-adjustable optical elements are poised to revolutionize both alternatives. Or, as Yogi Berra also said, “When you come to the fork in the road, take it.”
LOUIS E. PROBST, MD
The last decade has brought tremendous advancements in excimer laser technology, including scanning beams, eye tracking, iris registration, and wavefront technology. We have also learned not to use small optical zones and compressed gases on the stromal bed during the ablation. In 1995, the achievement of 20/20 UCVA in 50% of myopic eyes was successful. Now, we can achieve a UCVA of 20/20 in 90% of myopic eyes.
THE FUTURE
The next decade will bring refinements in the current excimer technology. Of course, the lasers will get faster, which will decrease stromal dehydration and improve outcomes. Faster eye trackers combined with iris registration will improve the placement of the laser treatment. Customized wavefront technology has been a welcome advancement, but the resolution of the systems will improve. All the current Hartmann-Shack aberrometers currently utilize 210 or fewer points, although topographers use thousands of data points to analyze the corneal surface. Wavefront analysis needs to be possible through the smallest pupils without being affected by accommodation. Transepithelial ablations of 8 to 9mm will allow an all-laser surface procedure, which will render epi-LASIK and other forms of epithelial removal obsolete.
NEW TECHNIQUES/TECHNOLOGY
The integration of the excimer laser with new techniques and technology will be a huge area of growth. The femtosecond laser will be gradually integrated into the refractive procedures until it is part of one machine rather than two separate units. Solid-state laser technology may compete with the excimer laser in the next 3 to 5 years. The limits and safety of mitomycin C for reducing haze after surface procedures will be defined. Corneal collagen modulators such as riboflavin with UV light may provide methods of improving the strength and stability of all corneas in the future.
IMPROVING RESULTS
Within the next 5 years, we should approach the 95% level for 20/20 UCVA for all forms of refractive error. With this level of success, LASIK's market penetration will eventually achieve the level of contact lenses today. Although some presbyopes will undergo refractive lens exchange, I do not believe this procedure will ever amount to more than 10% of the overall refractive market. The improvements and modifications I have outlined will keep the excimer laser and LASIK dominant for the next decade.
JOHN A. VUKICH, MD
It appears unlikely that the 193-nm excimer laser will be replaced anytime soon as the treatment of choice for most refractive errors. What does seem certain is that we will continue to refine our clinical results with incremental improvements. The acquisition of the wavefront error, translation of the wavefront map into a physical shape, and accurate delivery to the cornea form the essential chain of events in modern laser refractive surgery. A decade of experience with the 193-nm excimer laser has taught us that each step is important, and, in turn, each of the steps has been the focus of continuous development.
The fact that the technology is getting better does not necessarily make our job easier. Consistency and an attention to detail remain as important as ever. The difference now is that there are more steps to pay attention to. It is a paradox that, with each innovation, the role of the surgeon becomes more fundamental and ultimately remains the rate-limiting step. Nomograms are the direct result of the nuances of surgical technique such as treating a wet or dry corneal bed, the efficiency in delivery time, and the control of ambient temperature. Inherent in our ability to realize the full potential of present or future technology is the need to control these variables by precisely reproducing the same steps each and every time.
So, where do we go from here? In many ways, it is the same as it has always been. Our patients will get the best results from the meticulous application of the best available technology by a skilled and thoughtful surgeon.
William I. Bond, MD, FACS, is Director of Bond Eye Associates in Peoria, Illinois. He states that he holds no financial interest in any company or product mentioned herein. Dr. Bond may be reached at (309) 353-6660; bondeye@bondeye.com.
Stephen Coleman, MD, is Director of Coleman Vision in Albuquerque, New Mexico. He is a clinical investigator for Visx, Incorporated, but states that he holds no financial interest in any company or product mentioned herein. Dr. Coleman may be reached at (505) 821-8880; stephen@colemanvision.com.
Sheraz M. Daya, MD, FACP, FACS, FRCS(Ed), is Director and Consultant at the Centre for Sight, Corneoplastic Unit and Eye Bank, the Queen Victoria Hospital in East Grinstead, United Kingdom. He states that he holds no financial interest in any company or product mentioned Dr. Daya may be reached at
+44 1342 321 201; sdaya@centreforsight.com.
W. Bruce Jackson, MD, FRCSC, is Professor and Chairman of the Department of Ophthalmology at the University of Ottawa Eye Institute and Director General of the University of Ottawa Eye Institute at The Ottawa Hospital, General Campus in Canada. He is a consultant to Visx, Incorporated, and the Eye Institute receives research funding from Visx. Dr. Jackson may be reached at (613) 737-8759 or (613) 737-8374; bjackson@ottawahospital.on.ca.
Guy M. Kezirian, MD, FACS, is President of Surgivision Consultants, Inc., in Scottsdale, Arizona. He states that he holds no financial interest in any company or product mentioned herein. Dr. Kezirian may be reached at (480) 664-1800; guy1000@surgivision.net.
George Mintsioulis, MD, FRCSC, is Associate Professor of the Department of Ophthalmology at the University of Ottawa Eye Institute. He states that he holds no financial interest in any company or product mentioned herein He may be reached at gmintsioulis@ottawahospital.on.ca.
Louis E. Probst, MD, serves as Medical Director, TLC The Laser Eye Centers in Chicago, Madison, and Greenville, Illinois. He is a consultant for Advanced Medical Optics, Inc., and TLCVision. Dr. Probst may be reached at (708) 562-2020.
Robert K. Maloney, MD, is Director of the Maloney Vision Institute in Los Angeles. He has a financial interest in Calhoun Vision, Inc. Dr. Maloney may be reached at (310) 206-7692; drmaloney@maloneyvision.com.
John A. Vukich, MD, is Assistant Clinical Professor at the University of Wisconsin in Madison. He is a consultant to Staar Surgical Company but states that he holds no financial interest in any product mentioned herein. Dr. Vukich may be reached at (608) 282-2002; javukich@facstaff.wisc.edu.
1. Talamo JH, Krueger RR. The Excimer Manual: A Clinician's Guide to Excimer Laser Surgery. Little, Brown and Company; Boston, New York, Toronto, London. 1997.
