Customized Ablations #3: Getting Closer Yet
Customized Ablations: Getting Closer Yet
Irving J. Arons
Since I first heard about the possibility of enhancing vision via customized ablation from Marguerite Mcdonald's presentation at the 1998 AAO meeting, I have been intrigued with the concept. This interest was reinforced by a presentation given by Tim Turner, director of research at Orbtek, at the Spring 1999 ASLMS meeting, and by a tape of a course given at the 1999 ASCRS by the Autonomous Team, as I wrote in my column in the June 15, 1999 issue of Ocular Surgery News, "I've seen the future...and its CustomCornea".
Then, following last year's AAO meeting, I became convinced that the idea was viable and close at hand as I wrote in my column in the February 15, 2000 issue of OSN, "Customized ablations: the future is close". Now, following this Spring's ASCRS meeting, I have heard first hand of the early results on the initial human clinical trials and am convinced that custom ablation systems from several manufacturers will be coming to the market, perhaps as soon as the end of next year.
In an attempt to put this into perspective, I have interviewed all of the companies involved and have written descriptions of their programs as well as a side-by-side comparison of the specifications of their current laser systems in the accompanying table.
Before beginning, however, I should warn you that there are many problems yet to be resolved before routine customized ablations become the norm. Many questions remain to be answered:
● At what limiting age, considering the potential for cataract formation and the onset of presbyopia, should customized ablations not be considered?
● Should all higher order aberrations be corrected for? Can this be adequately done on the sub-surface of the cornea? What effective correction is achieved when performing customized LASIK on a patient following wavefront analysis, and then placing the flap back on top? Perhaps customized ablations ought to be done in two steps; perform LASIK with today's lasers, allow the cornea to stabilize, and then retreat/enhance to reduce some higher order aberrations for the best results. (What about the effect on correction of the smoothness of the microkeratome?)
● Can laser technology ablation-precision catch up with the precision of the diagnostic techniques? (LASIK done with wide-area ablation lasers increases higher order aberrations from 5-15 times, although the same procedure done using a small spot scanning laser employing an eye tracker can reduce the increase in aberrations to only 2-3 times that of the untreated eye. As one analyst has suggested, is wavefront sensing followed by LASIK an exercise in futility?)
● What about floaters? Will they show up on wavefront analysis, and since they move, how do you correct for them?
● What is the effect of the tear film?
● As Jack Holloday has espoused, what about corneal shape? Can most of the visual acuity be accounted for by just retaining the cornea's prolate shape, rather than making it oblate, as is done by most ablations today? (Should customized ablations be made to retain the corneas' asphericity?)
● And an even bigger question -- do most people really want to see 20/15, 20/10 or 20/8? Isn't 20/20 good enough? After all, this can be achieved routinely today. (Recall the story of the woman treated by Theo Seiler to 20/8 who couldn't watch television clearly, seeing only the raster lines!)
Assuming that all of the above questions -- and others that I haven't thought of -- can be eventually resolved, here is a company by company update of what each is doing to advance the state-of-the-art towards customized ablations.
Asclepion-Meditec, one of the pioneers in refractive laser surgery, who introduced their first excimer laser for medical applications in 1986, offers the new MEL 70 G-Scan, small spot scanning laser, incorporating a contrast-stabilized video active eye tracking system, that is capable of supporting either topographic or wavefront analyzed patients. The topographic supported customized ablation (TOSCA) system, operating for more than two years on more that 50 work stations installed worldwide, has been utilized in treating several hundred eyes with excellent results. Wavefront aberrometer supported corneal ablations (WASCA) is new this year, with a prototype Hartmann-Shack wavefront analyzer under evaluation, and about 30 eyes treated, with 3 months followup to date.
In addition to the above, new innovations from Asclepion this year include a cone for controlled atmosphere (CCA), to remove smoke and debris from the ablation field without causing dehydration of the corneal surface, and its tissue saving algorithm (TSA), used in conjunction with the TOSCA approach to remove up to 70% less corneal tissue.
Bausch & Lomb
B&L has launched Zyoptix, its new system for Personalized Vision Solutions, which incorporates its ZyWave Hartmann-Shack aberrometer coupled with its Orbscan IIZ multidimensional 3D corneal measurement device. This gives an integrated diagnostic for use with its Technolas 217Z Zylink software.
The laser uses a combined 2 diameter flying spot approach. First, a 2 mm spot is used to correct most of the refractive error, then the spot size is reduced to 1 mm to correct the fine structures, such as higher order aberrations. This, combined with a truncated gaussian beam, results in maximum smoothness of the corneal bed, minimal thermal effects, less tissue removal and a wider optical zone in an efficient treatment time. The company's laser also incorporates an active 120 Hz eye tracker.
LaserSight has taken a dual approach to customized ablations, introducing its line of Astra products. The company has developed both a topographical link to its LaserScan LSX laser, ASTRA (Advanced Shape Technology Refractive Algorithms), using corneal interactive programmed topographic ablation (CIPTA), for both irregular and regular corneal surfaces, with several thousand patients treated to date; but also, via the acquisition of diagnostic intellectual property from Premier Laser Systems earlier this year, will shortly have the capability to provide an integrated refractive diagnostic work station that includes front-to-back analysis of aberrations within the total eye. The CustomEyes system includes ASTRATrack, an eye tracking system designed to meet demands for performing the CustomEyes procedure; ASTRAPro, the software for planning the CustomEyes treatments; and ASTRAMax, the integrated ophthalmic diagnostic workstation that provides the data required to plan the CustomEyes treatment. The latter device uses a Hartmann Shack spatially resolved refraction system, that will be combined with 3D pachymetry, scotopic pupillometry and posterior corneal topography, to give an accurate measurement of total eye aberrations along with corneal shape and curvature.
LaserSight expects to complete its international trials and launch the topographic product in the international market during the third quarter of this year. U.S. clinical trials for the ASTRA technique are anticipated to be completed by year end with a U.S. commercial launch expected some time next year. The ASTRAMax refractive wavefront diagnostic should be ready for evaluation later this summer. Upon completion of development, the new work station will integrate wavefront analysis and corneal topography into a single instrument with additional diagnostic capabilities. ASTRA CustomEyes represents a new standard of eyecare that goes beyond conventional laser vision correction by individualizing the laser treatment utilizing a patient-specific set of diagnostic criteria intended to address and control both refractive error and optical aberrations.
The advanced diagnostic workstation will be employed with LaserSight's small spot scanning LaserScan LSX high-speed laser (100 Hz currently in the U.S., but 200 Hz internationally), along with the company's active video tracker (ASTRATrack) for stabilizing the eye.
Nidek has taken a different approach to customized ablation. First, the company has adapted its EC-5000 laser system to produce both a scanning slit for accomplishing most of the ablation, followed by converting the slit aperture to a segmented spot scan, using from one to six spots along the length of the slit, to complete the ablation -- somewhat similar to VISX's variable spot size laser, which uses its wide area aperture for about 80-85% of the ablation, followed by a small spot for "polishing" and customizing the correction. Since the six spot aperture has a spatial filter, the energy output of each spot is quasi-gaussian. The laser also employs an active video tracker with automatic centering, but which can be de-centered by the operator.
For the diagnostic input, Nidek uses a "souped-up" autorefracter, formerly known as the ARK 10,000, but now called the OPD-Scan (optimal path difference). It uses a slit lamp bundle of light that scans the retina (1440 measurements), a form of retinoscopy, with the reflected light signal picked up by photodetectors. In addition, the device employs topography to take accurate surface measurements which are combined with the retinoscopy to give refractive error through the whole pupillary area of the cornea, along with corneal shape. This information is fed into Final Fit software in a PC which calculates the ablation data needed for performing the customized ablation by the laser.
Currently, the ablation diagnostic data input is fed to the laser by means of a floppy disc, but eventually this could be done directly.
Schwind introduced its new sixth generation scanning small spot laser, ESIRIS, at the ASCRS meeting. This 1 mm spot beam, 200 Hz repetition rate laser, has been combined with an ultra-fast 300 Hz acquisition rate eye tracker and ergonomic design for an attractive package for performing LASIK and customized ablations. In addition, the company has developed ORK-link (Optimized Refractive Keratectomy), which connects either to a topographic system (Technomed C-Scan), or to its new Schwind Wavefront Aberrometer device for measuring optical aberrations. The latter is based on the Tscherning wavefront sensor developed by Theo Seiler and his team at Dresden University. To date, more than 120 patients have been treated with the system, and more than 1000 patients are expected to be treated by September of this year.
Based on 3-month followup results obtained on the first 30 eyes treated with the system by Prof. Seiler, 60% obtained 20/16 or better (10% achieving 20/10); and an additional 30% achieved 20/20. Thus, 90% of the eyes treated achieved 20/20 or better, compared to a side-by-side test of LASIK, where 85% were 20/20 or better, but only 35% were 20/16 or better.
Summit, one of the leaders in the wavefront customized ablation race, displayed its new LadarVision 4000 system, employing a 4000 Hz acquisition rate tracking system for stabilizing eye movement during ablation and built-in software for hinge protection during LASIK.
The major differences between the LadarVision system and its competition, is that the laser operates at the lower end of the repetition rate spectrum (60 Hz -- with only Asclepion-Meditec at 35-50 Hz and VISX at 10 Hz slower), while the company's tracker is at the high end (at 4000 Hz). Also, currently, wavefront measurements are taken on a dilated eye so that the company can deal with the type of aberrations that patients have to deal with during night driving. Research is underway to also evaluate undilated eyes, and to deal with both accommodated and unaccommodated states.
The first U.S. customized ablation was performed last October by Dr. Marguerite McDonald, using the Summit Autonomous CustomCornea analyzer and LadarVision system. Since then -- and through the ASCRS meeting -- about 35 patients have been treated (one eye with customized ablation and the other with either PRK or LASIK). Expanded U.S. clinical trials are currently underway. Early results from these trials indicate that some patients can achieve 20/12 vision, while others are getting 20/16. The company expects to complete its clinical trials and gain marketing approval for the system by the end of next year.
The wavefront device, which was demonstrated during ASCRS, takes five scans of the eye in a very short time, and selects the closest matching three scans for data input into the laser. The device, being built by Summit Autonomous' partner, Zeiss Humphrey, has been approved for marketing by the FDA and will be commercialized this fall.
VISX, like Nidek, has taken an interesting approach to customized ablations. The company's new Star S3 laser system employs "variable spot scanning", wherein the bulk of the refractive ablation will be done with its SmoothScan wide area ablation system, and final customized "polishing" will be done by a small spot scanning beam, ranging in size from 0.65 to 0.8 mm. Although the VISX SmoothScan is the slowest of all of the laser systems, operating at only 10 Hz -- with an upgrade to 20 Hz expected shortly, because it uses the full wide area beam for most of the ablation, total ablation time is equivalent to that of other systems (see the accompanying table). This technique also results in less ablation of tissue.
VISX has also added an active 3D infrared video eye tracking system to the Star S3 system, that tracks in the x and y as well as in the z axis, tracking the movement of the natural pupil.
The company's WaveScan Wavefront measuring system, developed by 20/10 Perfect Vision, is the only one with a patient feedback loop that provides the subject with an eyechart showing vision before and what it might be after customized treatment. The device, approved for marketing by the FDA, is expected to sell for about $75,000 and be available by the end of the year. Early results on 10 patients after 1 month, showed that 80% of WaveScan evaluated eyes had uncorrected vision of 20/15, compared to 60% of those treated based on manifest refractions.
The company expects to roll out the Star S3 laser by year's end, selling for $425,000, while current Star S2 users can obtain upgrades/conversions for $100,000. New laser purchasers can order Star S2s, which will include the upgrade and WaveScan (when available) for $425,000.
As previously written, the WaveLight Allegretto laser system is at the forefront of customized ablation, having been the first system used by Prof. Theo Seiler nearly a year ago (July 1999) in testing his Dresden Wavefront Analyzer. The Allegretto is small spot scanning system that operates at 200 Hz and has a 250 Hz active tracking system based on an infrared camera. This pupil-based tracker uses a patented illumination system to guarantee stable tracking throughout surgery, and is auto-centering, or can be decentered by the user.
An FDA clinical trial is currently underway in the United States for correcting myopia with LASIK. This trial will be expanded to include customized ablations, using a wavefront device based on the Dresden Analyzer, sometime in the near future. In European customized ablation trials, more than 60 patients have been treated with excellent results.
In late-breaking news, WaveLight and Coherent Medical have announced that Coherent will be WaveLight's exclusive marketing partner in Europe, Asia, and Latin America. No announcement has yet been made for the United States.