In the world depicted in comic books, krypton (kryptonite, actually) is a solid green substance from outer space which has paralyzing, even potentially deadly effects, on Superman -- and thus deemed by the law-abiding members of society as bad.
Not so in the real world, particularly in the field of ophthalmology where krypton is red, gaseous and good. Contemporary medical wisdom says the krypton laser is the best available treatment for the number one cause of blindness in North America, age-related macular degeneration (AMD).
But is it? Like a modern day scientific detective, Margaret Ballantyne, coordinator of the Canadian Ophthalmology Study Group in Kingston, Ontario, has been using workstations from Sun Microsystems running a visual data analysis software package, PV-Wave, to help Queens University Ophthalmology Dept. Chairman Dr. Alan F. Cruess answer that very question.
In the early 1980s, laser light was found to be an effective treatment for some retinal diseases, including AMD. Research suggested that the wavelength of green laser light was most appropriate for treating lesions outside the area of central vision. Other research concluded that red laser light was more effective for lesions in the area of central vision, medically termed the foveal avascular zone (FAZ).
Ballantyne's group sought to determine if red laser could also effectively treat lesions outside the FAZ, or if the green laser was still the better choice.
About AMD
AMD is a disease of the retina that causes cells to die. It is apparently caused by natural aging and may be accelerated by such things as prolonged exposure to sunshine or various biological and biochemical processes. Whatever triggers it, ultimately the retina does not get enough oxygen. This results in the formation of new blood vessels that carry more oxygen.
The FAZ is the area where the cones -- the eyes' color receptors -- are situated. This is where the nerve fibers are concentrated, helping the brain decipher what is seen. It's called an "avascular zone" because there should be no vessels present.
When AMD causes blood vessels to grow in this area, vision is impaired. The question of how best to treat this disease would have been a moot point just over a decade ago, but in 1983 researchers at Johns Hopkins University in Baltimore completed a four-year study that for the first time suggested a viable treatment for AMD. The lesions associated with the disease were treated with an argon green laser, causing them to photocoagulate, letting AMD sufferers maintain some of their visual acuity.
"People who were increasingly unable to read a newspaper were still reading five years after being treated with the argon laser," Ballantyne said. "They could read, write letters and watch TV -- things many of us take for granted every day. But to these people, it's a very big deal."
Red vs. Green
Then just a few years ago, Dr. Cruess was at Johns Hopkins when a new development in treating AMD occurred. The krypton red laser arrived and was touted as a potential improvement over the argon green lasers because the red light is better absorbed in the damaged area. If this proved to be true, it would likely lead to the replacement of argon green lasers with the new, more expensive krypton red lasers in hospitals and clinics throughout the world. This changeover would come at enormous expense to health-care providers and, ultimately, the public.
The Johns Hopkins researchers asked Dr. Cruess and his staff to undertake a comparative study to determine if the krypton red treatment was indeed a more effective laser treatment than the conventional argon green approach.
Dr. Cruess treated a random group of patients, some with the new krypton laser and some with the old argon laser. The patients were closely monitored after treatment and voluminous data was gathered concerning the relative progress of the two groups. It was at this point that Margaret Ballantyne and visual data analysis (VDA) entered the project.
The data collected was in the form of thousands of retinal photographs. Using PV-Wave, a VDA software program developed by Boulder, Colo.-based Visual Numerics Inc., on Sun Microsystems computers Ballantyne was able to compare successive photographs of an individual patient to determine the rate of laser scar growth.
The number and placement of these laser burns are the keys to understanding and monitoring the progress of the disease. "In AMD cases, the retina becomes hypoxic, meaning it desires oxygen," Ballantyne said. "It's not getting enough, so it creates its own blood vessels to look for the oxygen. These new vessels can cause hemorrhaging, resulting in lesions that raise the retina slightly, lifting it off its lower layer. This is what causes the vision to become impaired."
Tracking lesions
Tracking the exact placement and growth of these minute lesions through photographs requires absolute precision. For the purposes of the study, only patients with lesions in a tiny band some 2,000 microns wide surrounding the center of the retina were used.
Such determinations were made in the lab by Ballantyne, using a scanner attached to a Sun Microsystems Sparcstation running PV-Wave to analyze the photographic data. Measurements were compared with data generated from an enhanced image on PV-Wave and a cursor was used to draw around the edges of retinal scars.
According to Ballantyne, such detailed analysis would be impossible without this technology.
"It couldn't be done. If I want to look at the progression of scar growth, I can take a couple of patients and scan in all their photographs, bring one up on screen, and look at the percentage area the lesion is covering. Then I can bring up a photo that was taken of the same patient three months later and get the updated percentage.
"In the future, we hope to develop a package where images from the eye are directly enhanced and then analyzed by the same sophisticated software." Dr. Cruess said.
At one point, Ballantyne received an assist from Mike Mayer, a technical support engineer at Visual Numerics' field office in Cleveland.
"Mike helped me design a... program that let us bring up the first photo of the patient, look at the healthy blood vessels flowing through the retina, and match them up with the vessels from the same patient's photo months later. Then I could say ╘the lesion covers a larger area six months later,' and show that, indeed, it was bigger -- that it didn't just appear so because it was from a different camera angle."
Unconventional Wisdom
Preliminary data on a second study will soon be published and early results of the age-related macular degeneration study are already in.
"We found that we cannot agree with a popular position that the new krypton red laser is better," Ballantyne said.
"In fact, our research indicates that the argon green laser is actually more effective than the krypton red laser in preserving visual acuity of AMD patients."
So, what does this mean for doctors treating these patients? "It means that if you have argon green as your mode of laser therapy, keep it. There's no compelling reason to buy a krypton red laser. They're more expensive and harder to get."
While this is good news for both patients and those working in the ophthalmology field, Ballantyne sees it as a particularly welcome result for her homeland of Canada. "In Canada, it's much more difficult to pay for these lasers, because we have socialized medicine and the government has to approve everything. This is good news for the Canadian government, because it doesn't need to run out and supply our health care infrastructure with new lasers. And taxpayers can be happy about the cost savings."
Through the power of visual data analysis software, Ballantyne's group has shown that an existing therapy is not outdated and need not be replaced. Most importantly, this determination comes now before millions of dollars are spent on a needless changeover. It also means, should there ever be a real-life Superman, his X-ray vision would remain intact in his autumn years.
John Metzger is a free-lance writer based in Boulder, Colo. Formerly, he edited Architectural & Engineering Systems Magazine.