• Freezing Avastin May Reduce Its Efficacy
• Robots No Match for Ophthalmologists Yet
• New Hope for Patients With Tunnel Vision
• Gene Mutation Has Been Identified in Nystagmus
Freezing Avastin May Reduce Its Efficacy
Ophthalmologists might optimize their clinical results with bevacizumab (Avastin), particularly in macular edema, by not freezing the medication, a study by a German research group suggests.
The angiogenesis-blocking monoclonal antibody loses 10 to 20 percent of its effectiveness after being frozen to –20 C for five days and then thawed, said Swaantje Peters, MD, the lead author of the paper published online by the British Journal of Ophthalmology.1
Freezing the drug appeared to reduce its effectiveness in inhibiting cellular permeability, which underlies macular edema, more than it did to reduce the drug’s antiproliferative activity.
The results are very preliminary, and only some were judged statistically significant. However, they represent an important signpost on the road to understanding the ophthalmic effectiveness of a drug that was developed to stop blood vessels from growing in tumors. Bevacizumab’s use against age-related macular degeneration and diabetic macular edema has boomed over the last year.
Because treating cancer is the drug’s only approved use, ophthalmologists who want to use it must acquire a minimum of 100 mg of medication—80 times as much as the dose in one intravitreal injection. The paper by the Tübingen (Germany) Bevacizumab Study Group notes, “As the drug obtained from the pharmacy is not aliquoted for the intravitreal use, . . . it is common use to freeze aliquots for storage before injection.” How this affects the drug’s biological activity, and the accuracy of the presumptions about how bevacizumab works in the retina, have been unknown.
To find out, the researchers at University Eye Hospital Tübingen tested different doses of bevacizumab, both fresh and previously frozen, on cultures of porcine choroidal endothelial cells to which VEGF was added. To evaluate bevacizumab’s effect on cellular proliferation, the scientists added 50 ng/ml of VEGF to culture media that were evenly covered with endothelial cells, then scratched cell-free areas into the monolayers. Without bevacizumab, the endothelial cells multiplied quickly, leaving a cell-free area at the experiment’s end of 0.16 mm2. This compared with a cell-free area almost three times larger—0.46 mm2 (P < 0.005)—with fresh bevacizumab at a concentration of 0.5 mg/ml. But if the bevacizumab had been frozen, there was slightly less suppression of cell proliferation, and the cell-free area measured 0.41 mm2.
When looking at cell permeability, they found that increases in permeability of choroidal endothelial cells correlated inversely with native bevacizumab dosage. A dose of 0.1 mg/ml, well below the concentration in vitreous from a 1.25 mg dose, reduced permeability (P < 0.001). Multiplying the concentration tenfold reduced cellular permeability to levels similar to those seen in control cells.
At the 0.5 mg/ml dose, in cell culture with 50 ng/ml VEGF, the thawed bevacizumab allowed about 20 percent more leakage through cell walls, although the results did not achieve statistical significance.
Dr. Peters estimated that freezing the drug reduced its potency by 10 to 20 percent, and added that this drop-off would not be likely to worsen if the bevacizumab were kept frozen longer than the five-day period used in the study. “Usually the most stressing procedure for an agent is the freezing and thawing act itself, and not so much the continuous freezing time,” Dr. Peters said.
The paper does not address the possibility that a physician could overcome the loss of efficacy from freezing by increasing the dosage—that is, by drawing a 20 percent higher volume of the solution, or the equivalent of 1.37 mg of bevacizumab at the mixture’s original strength.
Currently, the research group is looking at bevacizumab’s ophthalmic cousin, ranibizumab (Lucentis), to determine whether it, too, is weakened by freezing.
1 Br J Ophthalmol. Published online Dec. 19, 2006.
In the OR
Robots No Match for Ophthalmologists Yet
Will tomorrow’s cataract patients look up from the surgery table at a robot instead of a physician?
That intriguing—or perhaps horrifying—prospect arises thanks to the arrival in ophthalmology of robotic ocular surgery. In a January article, one surgeon experienced with operating surgical robots and two ophthalmologists at the University of California, Los Angeles, published the first report of ocular surgery with a robot.1
“This is a good model for teaching surgical techniques and for the field of ophthalmic telemedicine,” said the study’s lead author, Angelo Tsirbas, MD, an assistant professor of oculoplastics at UCLA. “In addition, with some high-volume procedures like cataract surgery, you might be able to totally mechanize the whole thing.”
The robot’s formal name is the da Vinci Surgical System (Intuitive Surgical). Equipped with three arms angled at 45 degrees and a variety of other hardware, it looks like it should be chasing someone in a Terminator movie. But it waits quietly near the operating table for instructions from a surgeon seated at a virtual-reality console that can be situated across the room or thousands of miles away.
For the initial experiment reported by Dr. Tsirbas and two colleagues, Eric Dutson, MD, of the UCLA Center for Advanced Surgical and Interventional Technology, and Charles Mango, MD, now an assistant professor of ophthalmology at Cornell University, the console sat 15 feet away from the site where porcine eyes would receive corneal sutures.
With head and arms tucked partially inside the console, the surgeon viewed a 3-D image of the operating field provided by the robot’s two endoscopic cameras. The surgeon moved his hands as though they were performing the surgery, and the robot mimicked the movements.
So far, there’s no need for ophthalmic surgeons to worry about being replaced by a machine. Placing nine sutures in the three pig eyes took 465, 655 and 750 seconds with the da Vinci robot, compared with 183 and 190 seconds for two pig eyes under an operating microscope and direct human power. And, at more than $1 million each, a surgery robot hardly makes economic sense.
Indeed, surgery robots don’t have the immediately obvious advantages in ophthalmology that they have in other surgical fields, writes Raymond Douglas, MD, PhD, assistant professor of oculoplastics at the UCLA. But surgery by robot eventually “can provide the level of precision necessary to perform ophthalmic surgery with a short learning curve, improved speed and with-out mechanical tremor,” Dr. Douglas writes. “Utilization of robotic surgery and telemedicine may provide access to ophthalmic subspecialty surgery in geographically isolated areas.”
1 Br J Ophthalmol 2007;91:18–21.
New Hope for Patients With Tunnel Vision
Patients with severe visual field loss are taught to scan their heads from side to side to try to see their world, but their bumps and bruises give testimony to this technique’s limited effectiveness. Yet the devices available to cope with tunnel vision are limited, too.
Telescopic lenses can give affected people a better view of individual objects, but only within an even narrower slice of the visual field. When reversed, telescopic lenses minify images and thus widen the visible area—but the wearer no longer can see fine visual details.
Ideally, a more natural type of device for tunnel vision patients would accomplish both of those improvements at the same time, said Eli Peli, MSc, OD, and honorary PhD from Harvard, who is a senior scientist in aging-eye research at the Schepens Eye Research Institute and a professor of ophthalmology at Harvard University. And Dr. Peli may have developed a wearable electro-optical device capable of accomplishing this task.
In laboratory tests on 12 patients with tunnel vision, Dr. Peli and a senior scientific associate in his lab, Gang Luo, PhD, found that the augmented-vision, head-mounted device greatly improved patients’ ability to find targets projected outside their visual fields. They took 22 percent less time to find the targets, but the effect was measurable only if the patient’s natural field was at least 10 degrees.1
The spectacle-mounted system that Dr. Peli developed resembles the kind of see-through video displays that military pilots wear in front of their eyes. Images from a small video camera, attached to one temple piece, are minified four or five times before being displayed, so a view of a 40- to 50-degree area will fit inside a natural visual field of 10 degrees.
The pocket-sized computer makes translucent white outlines around all the objects in the minified video scene, eliminates everything else in it and then projects the ghostly outlines onto one of the spectacles lenses for retinal imaging. Thus, the wearer’s eye sees what it normally would, but superimposed over it is a miniature cartoonlike diagram of the wider field, which the computer updates 30 times a second. The idea is for the system to give the brain information for a mental map of where peripheral objects are located.
Dr. Peli said it might be three to five years before the device is available commercially for an estimated cost of $1,000.
1 Invest Ophthalmol Vis Sci 2006;47(9):4152–4159.
Gene Mutation Has Been Identified in Nystagmus
An X-linked form of idiopathic, congenital nystagmus has been associated with a specific mutated gene for the first time, a discovery that—if scientists are lucky—might eventually lead to clues about how to end this puzzling and debilitating condition.
Identified by a group at the University of Leicester in England, the mutated gene was present in 15 of 16 families in which every male had nystagmus and 50 percent of females did. Later tests found that 57 percent of the patients were from families with two or more affected members but no known family history of mutations in this gene, FRMD7. Among isolated cases in whom careful screening had eliminated all other known causes, 7 percent of those tested had mutations in FRMD7.
“The results suggest that mutation analysis of FRMD7 may be considered of diagnostic value even in isolated cases of either sex,” the authors write.1
How the malformed protein causes disease remains to be determined. However, similarities to another protein, which modulates neurite branching in embryonic rats, led them to a hypothesis: X-linked congenital nystagmus occurs because the aberrant protein alters the neurite length and degree of branching in neurons in the embryonic midbrain, cerebellum and retina.
“This will be the first time the mechanisms of nystagmus have been understood, and we hope it will lead to better drug treatments,” said study leader Irene Gottlob, MD, head of ophthalmology, Leicester School of Medicine. “[It] will also improve our knowledge of the control in eye movements in general.”
1 Tarpey P, et al. Nat Genet 2006;38(11):1242–1244.