THERMAL KERATOPLASTY REVISITED
Marshall reported that his group had hypothesized that the use of microwave energy could be targeted to “shrink” stromal collagen fibrils, both superficially and centrally within the cornea to correct myopia. This use of targeted microwaves could also be used in a peripheral ring to induce steepening of the cornea to correct hyperopia.
As I read the report, I was reminded that I had written about this very same thing nearly 20 years ago, in a “Technology Update” column written for Ophthalmology Management in October 1990. That column was titled, “The Rebirth of Thermal Keratoplasty (TKP)”, and told the story of Dr. Bruce Sands and his company Laser BioTech (which later licensed the technology to Sunrise Technology) trying to use targeted holmium laser energy to shrink collagen fibers, without thermal trauma, to flatten the cornea.
As background to this story, I also wrote about earlier attempts to use microwave energy to do the same thing, by a group that included Ralph Crump of Frigitronics (developer of the Softcon Lens – later licensed to American Optical) and Stuart Trembly of Dartmouth College. They were issued a patent that disclosed the use of microwave energy to shrink collagen tissue.
Nothing came from the microwave effort, and Sunrise Technology’s laser was marketed for a short time but the lack of precision in the shrinkage of collagen and a loss of effect lead to its demise.
The only company to take advantage of precise collagen shrinkage has been Refractec, with its Viewpoint CK conductive keratoplasty technique. This technique uses short pulses of radio-frequency energy introduced into short metal probes inserted into the cornea in a tight pattern for the correction of hyperopia.
Well, apparently there is a new company, founded by David Muller, the former CEO of Summit Technology and the above mentioned Stuart Trembly, called Avedro Inc. that is using microwave technology to successfully change the cornea's shape for correcting vision.
According to a recent filing with the U.S. Securities and Exchange Commission, the firm has raised an additional $10 million of equity venture capital funding to go along with its initial financing of $8 million.
Avedro's technology, called Keraflex, uses focused energy to reshape the front surface of the cornea. Avoiding the creation of a flap in the cornea or the need for the removal of any corneal tissue. Clinical trials will start shortly, followed by product launch in Europe.
As I learn more about this effort, I will report it in this space.
This column was published in the October 1990 issue of Ophthalmology Management.
THE REBIRTH OF THERMAL KERATOPLASTY (TKP)
Irving J. Arons
There is an old adage that says, "What goes around, comes around". And it looks like it will hold true again in the case of trying to change vision by applying heat energy to the cornea.
Over the years, there have been several attempts to change the shape of the cornea without surgery, by acting on the collagen lamellar that makes up the bulk of the stromal layer beneath the epithelium. The earliest attempts that I'm aware of were the application of a radio-frequency heating device to the surface of the cornea -- the Los Alamos Keratoplasty Technique(1) in the late 1970s. There have also been mechanical and chemical/mechanical means tried as well. In the mid 1970s, Charles Neefe of Midland, TX was issued a series of patents that disclosed the use of drugs to soften the collagen, followed by the application of rigid contact lenses to reshape the softened tissue(2). Then of course, there is the application of a series of ever tighter rigid contact lenses to correct high myopia (orthokeratology).
More recently, two newer methods of shrinking collagen have surfaced. The first, discussed at the 1988 AAO meeting in Las Vegas, involves equipment and a technique developed by Dr. Svyatoslov Fyodorov, of the Moscow Research Institute of Eye Microsurgery. A special handpiece is applied to the corneal surface and rapidly heated to 60°C and held at temperature for 0.3 seconds. By applying an RK type pattern to the cornea, Dr. Fydorov claims to obtain changes of 2-4 diopters with his thermocoagulating unit for thermokeratoplasty (TKP). Several US ophthalmologists have been trained in the technique and reportedly, Alcon Labs has obtained a license to develop the instrument(3).
This past July, a Business Week article(4) drew attention to a patent obtained last November by Ralph Crump (formerly President of Frigitronics) and Stuart Trembly)a professor of engineering science at Dartmouth College). The patent discloses the use of microwave energy to shrink collagen tissue in the mid-stroma. This device is reportedly in early stage development, with testing proceeding on removed animal eyes.
The most recent technology disclosure, and perhaps the most interesting, is the use of lasers to selectively shrink targeted collagen sectors in the mid-stroma, by raising the collagen's temperature by about 23°C above ambient with microbursts of energy. According to Dr. Bruce Sand(5), CEO of this yet little known company, Laser BioTech, Beverly Hills, CA, the laser energy is used to cause shrinkage of the collagen fibers to about one third their length, without causing thermal trauma to trigger a wound response and thereby negate the shrinkage. Animal experiments have shown that with a controlled burst of energy, myopia, hyperopia, and astigmatism can be corrected without effecting either the epithelium or endothelium. True intrastromal shrinkage without thermal trauma and subsequent collagen coagulation has been accomplished using bursts of 3-10 millisecond pulses with relaxation intervals of 50-200 milliseconds, from a 2.1 micron holmium-doped pulsed YAG laser. The total energy density is up to 100 joules/sq.cm. According to Dr. Sand, their patent application covering the technique has been allowed and will issue later this summer or by early Fall.
Laser BioTech was incorporated in 1986, and in conjunction with Medical Optics, Inc., a subsidiary of Kaiser Electro-Optics and Kaiser Aerospace and Electronics, has built and tested the prototype design of the solid state laser. The privately held company is currently seeking corporate sponsorship to expand the animal trials and further develop this unique concept into a clinical instrument.
Look out Phoenix Laser, ISL, Summit, Taunton and Visx, there's another company with interesting new technology looking in through the crack in the door!
NOTE: In my July/August column, "Report from ARVO", I also noted that work on laser thermokeratoplasty was being investigated with a Ho:YAG laser by a research group in West Germany, headed by Theo Seiler.
1. Rowsey et al, "Los Alamos Keratoplasty Techniques", Contact Lens Medical Jnl, Jan/Mar 1980.
2. A series of US Patents issued to Charles Neefe from 1973-1976.
3. "Hyperopic Surgery Kindles Heated Debate", Review of Optometry, January 1989.
4. Developments to Watch, "Clearing up Cloudy Vision -- with Microwaves", Business Week, July 2, 1990.
5. Private correspondence with Dr. Sand, August 1990.