Safer eye surgery

Citation

(2002), "Safer eye surgery", Sensor Review, Vol. 22 No. 1. https://doi.org/10.1108/sr.2002.08722aab.004

Safer eye surgery

Safer eye surgery

Keywords: Medical, Vision

Precision is crucial during eye surgery, because a slight miscalculation could result in partial blindness or damage to the retina. A new sensor being developed by the Department of Energy's Pacific Northwest National Laboratory in Richland, Washington could reduce risks by alerting surgeons to the location of critical retinal tissues.

PNNL researchers, in co-operation with Johns Hopkins University Microsurgery Advanced Design Laboratory and Insight Instruments of Sanford, Florida have designed and built a proximity sensor that can be attached to the tip of an endoscope, the tool that surgeons use to operate on the back of the eye. The sensor sends out an audible signal when the tool approaches the retina.

The proximity sensor relies on a fibre, smaller than a strand of hair, to transmit and receive light. The system sends electricity into a laser diode that connects to a fibre. Because of the eye's sensitivity, the laser cannot exceed 37 microwatts. The diode converts electricity into light, which then bounces back and forth along the fibre walls until reaching the retina.

The retina absorbs about 80 per cent of the energy and reflects the remaining 20 per cent back to the proximity sensor. The reflected light travels back through the fibre to a photo diode, which converts the light into an electrical signal. An electronic signal converts the voltage signal into distance. If the distance reaches two millimetres or less, the system triggers an audible alarm to alert the surgeon.

One challenge in designing the sensor was sensitivity, according to Peter Eschback, a senior research scientist at PNNL's sensor group. The proximity sensor had to be 100 microns in diameter, small enough to fit through the 19-gauge needle of the endoscope. The small size made it more difficult to collect light, so sensitivity is diminished.

The optic fibre is configured like a "Y" using a 2x1 fibre coupling device. At one branch of the Y is a photo-diode detector. At the end of the other branch is the emitter. The stem of the Y is connected to the endoscope. The emitted light travels to the sense fibre; returning light goes through a 90/10 splitter, sending 90 per cent of the light to the detector. The configuration diverts most of the returning light to the detector and is said to be easier to implement on endoscopes.