To repair holes in the eye’s macula, the area responsible for crisp vision, ophthalmologists must peel back a membrane that is thinner than plastic wrap. Involuntary movements or tremors can traumatize surrounding tissue and cause myriad complications. A significant reduction in tremor would allow surgeons to improve their accuracy as well as the safety of surgical procedures.
While tremors are not visible to the eye, they occur at the end of a microsurgical instrument whose diameter ranges from 0.5 mm to 0.9 mm, less than the width of a human hair. A research group at Carnegie Mellon University led by Associate Research Professor Cameron Riviere has developed a completely handheld device that nearly eliminates these tremors.
The micromanipulator uses an optical tracking and filtering system to adjust for unwanted movement. The optical tracking system captures signals from two small light-emitting diodes (LEDs) on the end of the device and relays them to two position-sensitive detectors that filter and process the signals in two parallel paths. The system senses its own motion, distinguishes between desired and undesired motion using advanced filtering techniques, and deflects its own tip to compensate for the undesired motion.
“In theory this [the micromanipulator] could become the standard instrument for certain high-precision procedures,” says Riviere, who plans to begin in vivo tests on animal models next year and expects the device to be ready for clinical work within 5 years.
Opening Up New Surgical Opportunities
Although a number of microsurgical fields, such as neurosurgery and cardiology, could benefit from adoption of the micromanipulator, eye surgery will likely be the first field to use the device. “We’re focused on the eye because that’s where there is the greatest clinical demand,” says Riviere. The eye’s delicate structures and rich network of blood vessels make it difficult for surgeons to treat some retinal conditions using current technology.
For instance, removal of blood clots that form on the retina is essential to maintain sight. Clinical attempts have been made to break up clots but “it’s generally not feasible today for most surgeons,” says Riviere. The procedure requires an eye surgeon to inject a clot-dissolving drug into the retina’s tiny vessels. “The vessel can tear because of the shakiness of the [surgeon’s] hand,” Riviere explains. The new instrument would allow the surgeon to manipulate the vessels with the accuracy of a robot and the ease of a simple handheld tool.
Another retinal procedure involves removing scar tissue. “Peeling scar tissue off of the retina is like taking scotch tape off of a table top with tweezers the size of a sewing needle,” says James Handa, Associate Chief of the Retina Division, Johns Hopkins University, who has used the device in a laboratory setting. “Oftentimes the scar tissue is nearly invisible so dexterity is extremely important,” he says. The device would allow surgeons to grab hold of the scar tissue securely and remove it. It also has the potential to improve the safety profile of every surgery, says Handa.
Because current technology does not permit ophthalmologists to probe below the retina’s surface, one of the only options to treat melanoma in the eye is global chemotherapy given directly to the eye. The highly toxic drugs can damage sensitive eye structures. However, the micromanipulator would enable surgeons to open blood vessels that feed the tumor and inject high-dose chemotherapy directly into the vessels. This localized method would spare sensitive eye structures.
Yet another avenue where the micromanipulator could make a difference is in repetitive motion procedures such as scanning with a laser, says Louis Lobes, Clinical Associate Professor of Ophthalmology at the University of Pittsburgh Medical School, who has worked with Riviere on the project.
Currently, eye surgeons use patterned laser treatments to seal retinal tears and prevent regrowth of abnormal blood vessels in diabetic retinopathy. In the latter case, a surgeon points a laser and presses a foot pedal to activate a light pulse. A surgeon may need to direct the probe to trigger up to 1,500 individually aimed pulses over the entire retina, but surgeons often feel fatigue after about 600 shots. With the micromanipulator’s software, surgeons could simply aim the laser at the center of a preprogrammed pattern, engage the foot pedal, and the device would automatically scan through the pattern.
Where No Surgeon Has Gone Before
The micromanipulator’s compact design, relatively low cost – about $1,000 – and ease of use could give the device an edge over large robotic-assisted surgery systems. The device runs off of a personal computer and is handheld like today’s passive microsurgical instruments. It also has the ability to be shut off and operated as a passive device if a patient’s condition warrants.
The micromanipulator’s potential is tempered by a few remaining technical challenges that Riviere and his team must overcome. These include reducing the manipulator’s size, improving its range of motion so it can swivel 360°, and convincing surgeons to use the device.
“The biggest impediment is changing the mentality,” says Handa. “Many surgeons will say, ‘Who needs that?’” But Handa and Lobes both agree that the device improves their surgical abilities. “What this does is enhance the ability of the surgeon to do finer and finer procedures,” says Lobes. “Surgery is mostly about action and reaction. Neutralizing a tremor makes a surgeon more confident.” Adds Handa, “This could allow average surgeons to become outstanding and gifted surgeons to go places they’ve never gone before.”
This research is funded in part by the National Institute of Biomedical Imaging and Bioengineering and the National Eye Institute.
MacLachlan RA, Choi DY, Lobes LA, Riviere CN. Compensation of tremor by an active handheld micromanipulator. IEEE Transactions on Robotics. In press.
MacLachlan RA, Riviere CN. Optical tracking for performance testing of microsurgical instruments. Pittsburgh, PA: Robotics Institute, Carnegie Mellon University. Pa. Tech. Rpt. CMU-RI-TR-07-01, 2007 Jan.
Riviere CN, Gangloff J, De Mathelin M. Robotic compensation of biological motion to enhance surgical accuracy. Proc IEEE. 2006;94(9)1705-16.