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17 Jun 2002
A fibre-optic proximity sensor that could help to protect the retina during eye surgery will be tested on patients next year.
The device, which alerts the surgeon if their tools come too close to the eye, is being developed at the Pacific Northwest National Laboratory (PNNL) in collaboration with Johns Hopkins University's Microsurgery Advanced Design Laboratory and Insight Instruments.
The sensor is based on a 125 micrometre diameter optical fibre connected to a laser diode, which transmits 850 nanometre light to the retina or other sensitive features in the eye. The retina absorbs about 80% of the energy and reflects the remaining 20% back to a photodiode in the sensor. This converts the light into an electrical signal and the voltage corresponds to distance. If the tool is two millimetres or closer to the retina, the system triggers an audible alarm.
Pacific Northwest researchers tested this idea in 1998 and are now building a proximity sensor specifically for eye surgery. In particular, the laser power must be restricted to prevent damage to the eyes. Pete Eschbach, the principal investigator at PNNL, says that the sensor delivers a power of about one microwatt to the back of the retina. "We have done calculations that indicate concern only when the power approaches or exceeds 40 microwatts," he explained.
Clinical trials will be carried out at Johns Hopkins University and, if these are successful, Insight plan to integrate the proximity sensor into the endoscopes they market for eye surgery.
The developers of the sensor anticipate other surgical applications, such as locating nerves during spinal operations.
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