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Customized ablations: the future is close
Several companies are developing wavefront analysis and ray tracing technologies for designing ablations.
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At the 1998 meeting of the American Academy of Ophthalmology (AAO), some of us learned about customized ablations, as several firms announced plans to tie corneal topography to their lasers and use this diagnostic input to drive the ablation program. In addition, as I reported in the June 15, 1999 issue of Ocular Surgery News (page 53), Autonomous Technologies (Orlando, Fla.) was leading the way in going beyond topography to wavefront analysis.
Well, technology has taken a major leap forward. Forget topography-driven ablation — although it will aid in treating corneal defects such as astigmatism. Wavefront/ray tracing analysis is closer than any of us thought. At the 1999 AAO meeting, I witnessed demonstrations of no less than three new wavefront and one new ray tracing devices.
The Autonomous wavefront device, in conjunction with its LadarVision excimer, now has been used to treat human eyes. Marguerite McDonald, MD, reported very early results of her first 5 patients, treated on Oct. 12, 1999. Theo Seiler, MD, of Dresden, Germany, reported on his first dozen patients, treated in July and August, using his Dresden Wavefront Analyzer and the WaveLight (Erlangen, Germany) Allegretto scanning spot excimer laser. The Dresden Wavefront Analyzer also will be used with a new small spot scanning laser about to be introduced by Schwind eye-tech-solutions of Kleinostheim, Germany.
In addition to the Autonomous CustomCornea Measurement Device and the Dresden Wavefront Analyzer, to be distributed by Technomed GmbH of Baesweiler, Germany, Visx (Santa Clara, Calif.) unveiled Josef Bille’s 20/10 Perfect Vision (Heidelberg, Germany) wavefront device. Bausch & Lomb Surgical (Claremont, Calif.) demonstrated a prototype of its aberrometer/wavefront analyzer (developed by Technolas GmbH of Munich), to be coupled with its Technolas 217C excimer laser, which appears to operate in a similar fashion to other wavefront devices.
It is my understanding that the aberrometer probably will be incorporated into B&L’s Orbscan, to provide maximum information about both the cornea and internal aberrations of the eye system.
I also saw a demonstration of a new ray trace device from Tracey Technologies (Bellaire, Texas), formed by Joe Wakil, to commercialize this new device developed in Russia. The device was discovered by Ioannis Pallikaris, MD, of Greece, who used it to run some of the first experiments on human eyes at the University Hospital of the University of Crete. Dr. Pallikaris is a co-founder of Tracey Technologies. The Tracey device is an electro-optical ray tracing analyzer that measures refraction in real time, to ±0.20 D and, according to its developers, may be more versatile in measuring aberrations of the eye than wavefront devices.
It appears that some of these devices will be available as early as the American Society of Cataract and Refractive Surgery (ASCRS) meeting in Boston. At that point, their use will be mainly as diagnostic tools to gather more complete refraction information, which then can be fed into current excimer laser ablation programs for achieving a higher percentage of 20/20 corrections than can be done today. It will probably be several years before wavefront-linked customized ablations will be generally available.
Meanwhile, topographic links are still moving forward, with several laser companies not yet working with wavefront technologies. These laser companies are striving to establish relationships with topography companies or devices. (See the accompanying table of which analytical/diagnostic devices each of the excimer laser companies is pursuing.)
Summit/Autonomous Technologies
Autonomous has spent more than 3 years working on its CustomCornea wavefront measuring device. These efforts are starting to bear fruit, with the first patients treated using the system. The Food and Drug Administration (FDA) accepted the company’s investigational device exemption for CustomCornea last July. The first of 40 patients have been enrolled in a phase 2-like feasibility study to determine calibration and safety, with doctors treating one eye with “traditional” laser in situ keratomileusis (LASIK) on the Autonomous Technologies laser and the other with CustomCornea-controlled LASIK.
Dr. McDonald was able to objectively measure the unique aberrations of each patient’s eye and treat the CustomCornea eye with an individualized ablation pattern to correct those aberrations. Autonomous expects it will take 1 to 2 years to complete its phase 3 clinical trials and be ready to submit data to the FDA. However, the company expects to be able to market a stand-alone diagnostic device sometime next year, which laser users will be able to use to achieve better refractions to feed into the laser’s ablation program, and has recently announced a joint venture with Zeiss/ Humphrey Systems (Dublin, Calif.) for Zeiss/Humphrey to manufacture and market this diagnostic device.
Autonomous believes it has an advantage over others working with wavefront technologies, because of its LadarVision system and its unique eye tracker. The company believes the combination of a small spot scanning laser and the ability to place the correction precisely where it is needed gives it a step up on its competition.
Visx, 20/10 Perfect Vision
At a presentation sponsored by Visx, Josef Bille, the founder of 20/10 Perfect Vision, explained how he got involved in developing his wavefront analyzer, to be marketed by Visx under an exclusive worldwide agreement. Mr. Bille, the director of the Institute of Applied Physics at the University of Heidelberg and a founder of both Heidelberg Engineering and Intelligent Surgical Laser, originally developed the technology in the 1970s for use in astronomical applications, with the first German patents filed in 1982 and issued in 1986. In 1997 through 1999, he co-founded 20/10 Perfect Vision and filed additional patents covering later developments.
The technology is based on adaptive optics to compensate for aberrations using a deformable mirror, which has been reduced in size to a microchip array today and speeds up the testing time to less than 15 seconds. A laser signal is imposed onto the retina, and the return signal is analyzed to form an acuity map and a differential acuity map, which are used to achieve a simulation of best acuity. This data can be used to make an exact contour ablation of the cornea. Visx intends to incorporate the technology into a diagnostic device, which the company hopes to make commercially available in 2000.
The real question is how Visx intends to couple the diagnostic tool to their laser. According to experts in the field, a rapid firing, small spot scanning laser is needed to place a precise ablation pattern on the cornea, and a tracking de vice is needed for this precise placement. Visx currently can scan a small spot, but at a rather slow scanning rate (50 Hz), and does not, to my knowledge, have a precise tracking device for their laser system. Perhaps they will acquire the technologies needed to commercialize their wavefront technology for customized ablations.
A Visx spokesperson said the company plans to have active eye tracking and rapid small spot scanning capability in fiscal year 2000. The Star S2 has already demonstrated its ability to deliver ablations as small as 1 mm in diameter via its Contoured Ablation Pattern (CAP) Method for treatment of irregular corneas (currently available for international use only). Theoretically, it would not be necessary to do an entire custom ablation with a small spot but rather with a combination of broad area ablation followed by small-spot contouring.
Dresden Wavefront Analyzer/Technomed
Developed by Dr. Seiler and colleagues at the Department of Ophthalmology, University Eye Clinic, Dresden, Germany, the Dresden Wavefront Analyzer is based on the Tschernig aberroscope, first described in 1894. A bundle of equidistant light rays is projected onto the cornea and, due to optical imaging, becomes focused on the retina. In an aberration-free eye, the retinal image pattern consists of equidistant light spots. However, the spot pattern of a normal eye is distorted by ocular aberrations. The deviation of spots from the ideal pattern is measured by an indirect ophthalmoscope and directed to low-light CCD linked to a computer. These patterns are used to compute wavefront aberrations.
When this data is integrated with preop corneal topography, an ablation profile is computed and used to feed the excimer laser to correct all the eye’s aberrations. By reducing ocular aberrations and adjusting for effects of the pupil size, visual acuity can be dramatically improved — approaching 20/15 or better.
The Dresden Wavefront Analyzer uses a frequency-doubled Nd:YAG laser at 532 nm and a mask system to create 168 equidistant and parallel light rays for projection onto the cornea. Exposure time is 40 ms. The precision of the device allows objective measurement of spherical and cylindrical refractive error with an accuracy of better than ±0.25 D.
The device will be marketed by Technomed Technology and will be coupled with excimer laser systems from both WaveLight Laser Technologies AG and Schwind eye-tech-solutions.
WaveLight Laser Technologies AG
The Dresden Wavefront Analyzer was used with WaveLight’s Allegretto excimer laser to treat the first human patients in March 1999. In July, Dr. Seiler used the system to treat the first patients under the WaveLight protocol. The postop vision of the first seven patients was two to three times as sharp as that of someone with 20/20. Of the first 12 patients treated, three have achieved 20/15; two are at 20/10; and one has achieved 20/8.
Dr. Seiler told of one patient treated who reached 20/8. Doctors in attendance were overwhelmed by her visual acuity, but the woman complained that she was unhappy with her new vision, as she could no longer watch TV. It seems instead of seeing clear pictures on the screen, she now sees the raster lines! Additional patients have since achieved 20/8 without that problem.
The WaveLight Allegretto laser is a small spot (1 mm) scanning system. It operates at 200 Hz repetition rate and uses a 250 Hz active tracking system, based on an infrared camera. The pupil-based tracker uses a patented illumination system to guarantee stable tracking throughout surgery, independent of ablation type or quality of the keratome cut. It can be selected for self-centering or decentered as desired.
WaveLight is undertaking a European study of low to moderate myopia with astigmatism that will be done according to FDA protocols for possible use in an FDA submission for U.S. marketing approval. One hundred fifty patients from –1 to –10 D, with 0.25 to 2 D of astigmatism, will be included. The Dresden Wavefront Analyzer will be used on both eyes, and bilateral LASIK will performed using the Bausch & Lomb Hansatome, the Schwind Supratome or the Moria CB keratome.
Schwind eye-tech-solutions
The Dresden Wavefront Analyzer also will be used with a new Schwind sixth generation scanning spot excimer laser with active tracking. The laser will operate at 200 Hz and will have a 250 Hz passive/active eye tracker, which corresponds to a reaction time of 4 ms.
Pulse repetition on a single point will be less than 35 Hz, to avoid local heating of the corneal tissue. It is expected that the ablation area will be smooth, created by a 0.9 mm gaussian laser spot. The system will combine all standard treatments, along with customized ablations, based on either topographic or aberrometric diagnostic in formation. Dr. Seiler said this new laser creates the smoothest ablations he has seen. It is expected to be unveiled at the upcoming ASCRS meeting, at which time more details will be available.
Bausch & Lomb/Orbtek
Not much technical information was provided about the new aberroscope being developed by B&L for use with its Technolas excimer laser. The device demonstrated appeared to be a Hartmann-Shack type system, operating in a similar fashion to those from Autonomous, 20/10 Perfect Vision and Dresden.
Similar ablation maps were created, but currently there are no details of how this device would be linked to the Technolas laser. It is assumed the analyzer will be combined with the Orbscan, to provide total eye system aberration measurements. No information was provided about whether Bausch & Lomb intends to commercialize the aberroscope as a free-standing diagnostic system.
Tracey Technologies
The final device shown at AAO for measuring the abnormalities of the refractive system of the eye was the Tracey Ray-Tracing Refractometer. Unlike Hartmann-Shack-type devices, the Tracey device uses the thin beam principle of optical ray tracing to measure the refractive power of the eye on a point-by-point basis. According to Tracey Technologies, its ray tracing device measures one point in the entrance pupil at a time, rather than the entire entrance pupil at once, like aberroscopes and Hartmann-Shack devices, with the possibility of data points criss-crossing in a highly aberrant eye.
The device is designed to rapidly fire a series of parallel light beams one at a time, within microseconds, into the eye, passing through the entrance pupil in software-selectable patterns. Semiconductor photodetectors detect where each light ray strikes the retina and provide raw data measuring the x-y error distance from the ideal conjugate focus point, giving a direct measurement of refractive error for that point.
Because of the high speed of the system, 64 points within a 6 mm pupil can be measured five times each in just over 10 ms, greatly increasing the accuracy and reproducibility of the system. The Tracey system can measure a large dynamic range of aberrations, which should provide an advantage when measuring the eye, with its range of refractive errors. The Tracey system can provide full calculation of wavefront deformation and modulation transfer function of the eye.
Tracey Technologies expects to have its device ready for commercialization within 3 to 6 months, priced in the range of a premium topographer.
Although all three of the techniques for measuring aberrations of the eye — the aberroscope, Hartmann-Shack analyzer and ray tracing — can provide a map useful for determining ablation patterns, Tracey claims its device has a greater speed of measurement, greater reproducibility and more flexibility. Only time will tell which type of device is preferred by the marketplace.
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