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News in Review
A Look at Today's Ideas and Trends
Virtual Phaco Used as an Aid in Training
When New York surgical resident Elad Feldman, MD, performed his first capsulorhexis, he could thank about 100 virtual patients for showing him how.
“It’s a really daunting thing for any new surgeon to be in a human eye for the first time,” Dr. Feldman recalled this spring, shortly before completing a residency at New York Eye and Ear Infirmary. “I probably did 100 virtual capsulorhexes before I did that first rhexis in a living human eye.”
Dr. Feldman’s virtual cataract surgeries took place on the EyeSi, a sophisticated simulator for teaching ophthalmic surgery techniques. EyeSi has been available for teaching vitreoretinal procedures for several years; however, the device’s German manufacturer, VRmagic of Mannheim, developed software to teach anterior segment surgery, which the company began selling this year.
From two oculars through which the user views the virtual surgery on an artificial head, to foot pedals for controlling phacoemulsification power, aspiration and flow, EyeSi gives the user a surprisingly realistic experience, better than can be achieved with pig eyes in the lab, said Richard B. Rosen, MD, vice chairman of ophthalmology at NYEE.
“They’ve done a tremendous job in terms of engineering this. You have a sensation that is pretty close to what you would be having if you were in the operating room,” said Dr. Rosen, who spearheaded NYEE’s acquisition of the EyeSi while he was serving as director of residency training. “This adds a tremendous level of safety to learning cataract surgery.”
No two simulations on the device are the same because the user’s surgical choices govern how the “case” goes, said VRmagic’s president, Markus Schill, PhD, a physicist who began working on the simulator while at the University of Mannheim. “We developed mathematical models that describe the physical properties of every structure in the eye, then solve the mathematical equations over time, very rapidly, to calculate the reaction of tissue to surgical manipulation,” Dr. Schill said.
Experience on the simulator helps the user gain body memory of the special coordination of hands and feet required during phaco, Dr. Feldman said. “You have to use both hands and both feet, and that’s not something that you normally would do every day. To get the coordination to have them all working together simultaneously takes practice. And most surgeons would rather practice on a computer than on a patient.”
At a cost of more than $100,000, EyeSi likely will be within the financial reach of only academic centers or the largest group practices. However, ophthalmologists who do have access to EyeSi could use it to monitor or sharpen their own performance.
“The interesting thing is the simulations don’t really get boring because the experience is novel every time you do it,” Dr. Rosen said. “You may have done it 50 times, but if you’re tired and you do a procedure in the machine you’re going to mess it up.”
For more information, visit www.VRmagic.com.
Functional Keratocytes Made From Bone Marrow
Injected into the cornea, mesenchymal stem cells taken from bone marrow apparently contain the correct molecular signaling apparatus to differentiate into keratocytes and secrete a molecule critical to building the extracellular matrix, says a study by scientists at the University of Cincinnati.
“We found that bone marrow stem cells can contribute to the formation of connective tissues,” said Winston Whei-Yang Kao, PhD, professor of ophthalmology and senior author of a paper presented in May at the annual meeting of the Association for Research in Vision and Ophthalmology.1
The genetic defects in more than 20 corneal dystrophies cloud the cornea by preventing keratocytes from producing various proteoglycan molecules that, over the last decade, have been shown to be necessary for the correct arrangements of the layers of collagen fibrils in stroma.
In their study, Dr. Kao and colleagues injected stem cells from normal mouse bone marrow into the corneas of a strain of knockout mice whose keratocytes cannot express keratocan, a matrix proteoglycan. Seven days after injection, the stem cells began looking like keratocytes and produced keratocan.
Would stem cells from human bone marrow also normalize extracellular matrix components such as keratocan in dystrophic human corneas, repair their matrix and restore vision? The group plans to seek answers to these questions with a clinical study in Taiwan, in collaboration with an ophthalmologist who trained in Cincinnati.
1 Liu, H. N. et al. Bone marrow cells can differentiate and assume keratocyte characteristics of keratocan expression in mouse corneas. Presented at ARVO, May 9, 2007, Ft. Lauderdale, Fla.
Cataract Surgery–IOP Link Further Explored
The idea that intraocular pressure falls after cataract surgery isn’t new, but a retrospective review of more than 600 cases suggests a greater effect than previously thought—perhaps large enough in some patients to prevent ocular hypertension from progressing to glaucoma.
The study showed the IOP decrease in eyes without glaucoma lasted up to nine years and was directly proportional to the preoperative pressure. For the 88 eyes with IOP of 20 to 27 mmHg before the surgery, the decrease averaged 5.5 mmHg one year after surgery with a postop pressure rise of 0.4 mmHg on average during follow-up of one to nine years. The average one-year decrease was even larger—6.8 mmHg—for eyes with preop pressures of 23 to 27 mmHg.
“Never in my wildest dreams did I think that some of the pressures would go down by nearly 7 mmHg,” said study leader Brooks J. Poley, MD, of the research he presented at the spring meeting of the American Society for Cataract and Refractive Surgery (ASCRS) in San Diego. Dr. Poley is a Minneapolis ophthalmologist now retired in Bluffton, S.C.
The overall drop in IOP revealed in the patients’ charts was a modest 1.7 mmHg, similar to the 1.4 to 1.7 mmHg average pressure decreases reported in 2006 for a series of glaucoma and nonglaucoma eyes, after five years of follow-up.1 These similarities suggest a need for new analysis of data in earlier studies of IOP after lens exchange, to look for stratification of effects, Dr. Poley said.
Though he was still analyzing the results for statistical significance in late spring, Dr. Poley was enthusiastic about the possibility that the study’s results might point to a new direction in glaucoma prevention. His working hypothesis is that aging increases the lens’ volume after the rest of the eye stops growing, and that pseudophakia opens up the crowded trabecular meshwork to lower IOP persistently.
Multifocals May Hamper Later Retinal Surgery
Though increasingly popular to treat presbyopia, multifocal intraocular lenses might make subsequent vitreoretinal surgery trickier to accomplish, a few voices in the ophthalmic community have begun pointing out.
David R. Hardten, MD, said at an ASCRS symposium last spring that the alternating zones of distance, intermediate and near correction in multifocal IOLs interfere with normal views of the retina. Dr. Hardten practices at Minnesota Eye Consultants, Minneapolis, as well as doing research, teaching residents and fellows and serving as an adjunct associate professor at the University of Minnesota.
He advises surgeons to consider sending patients who have epiretinal membranes to a retina specialist for vitrectomy and membrane peeling prior to phacoemulsification and implantation of the multifocal IOL.
“Most retina specialists I’ve talked to have said they could do the procedure, but that it was a much more difficult dissection because of the multifocal optics,” said Dr. Hardten. “You’ve got one image on the retina that’s 3 D out of focus and one that’s in focus at any given point. There’s also a loss of depth perception.”
Richard B. Rosen, MD, a retina specialist and vice chairman of ophthalmology at New York Eye and Ear Infirmary, agreed about the extra difficulty. “I have had to repair a few retinas with those lenses in place, and it is much more difficult to see what you’re doing. You rely on light from the fiber optic bouncing back through the IOL, but the diffractive zones break it up. You’re trying to look at the entire retina, yet you have a very small area that you actually can see well,” Dr. Rosen said.
A dense cataract might prevent pre-IOL membrane removal, though. “If a patient with an epiretinal membrane really needs cataract surgery, you may not be able to do a good job peeling the membrane before the cataract surgery,” Dr. Rosen said. “That may be a really good reason not to put that kind of lens into that patient.”