OCT Integrated into Robotic Opthalmic Forceps

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Recently, there has been a lot of interest in the application of optical coherence tomography (OCT) to retinal surgery. While OCT is already established as a tool for diagnosis and pre-surgical planning, the idea of imaging during the surgery itself hasn’t found much traction. Initially, this was partly due to the lack of commercial OCT systems that were well-integrated with ophthalmic microscopes. This meant that the surgery had to be halted, the ophthalmic microscope removed, and the OCT slid into place every time an OCT image was wanted. More recently, Carl Zeiss and Haag-Steit have begun marketing devices where the OCT is integrated into the surgical microscope, so that both can be used simultaneously. The OCT images can then be displayed to the surgeon in the microscope view. However, the authors of a recent paper in Biomedical Optics Express claim that these integrated OCT systems are still not ideal. Instead, they propose an OCT scanner which is built into the surgical instrument itself.

In the paper 1, the authors’ main arguments against the current approach to intraoperative OCT are twofold. Firstly, they say that the surgical instruments cast shadows onto the OCT image of the retina. This is certainly true for stainless steel instruments, although there have been some attempts to build semi-transparent instruments for compatibility with OCT. The second argument is that it is difficult to track the position of the instrument in real time using the OCT image. They claim to solve both problems by adding an OCT probe of the instrument. Most of the shaft then lies behind the OCT optics, although there is still some shadowing from the gripper, and if the retina can be identified in the OCT image then the distance from the tool is known immediately.

The idea of adding an OCT channel to a surgical tool is not new; Jin Kang’s group at John Hopkins have done extensive work on integrating a non-scanning OCT probe to surgical tools, but these systems only produced A Scans (1D depth profiles). By comparison, the instrument reported here produces forward-facing B scans (2D cross-sections), despite having an outer diameter of just 0.51 mm. The probe is essentially a single mode fibre and an electromagnetic linkage for scanning at 5 Hz, while a GRIN lens provides focusing. The price to be paid for the small diameter is resolution – the authors achieve 35 microns centrally and as poor as 45 microns at the edge of the field of view.

For this study, the authors were particularly interested in using OCT with robotic ophthalmic surgery, and so they manipulated their custom instrument using a seven degree of freedom robotic arm. They performed several experiments using phantoms and ex vivo animal retinas, and were able to show that the OCT guidance improved performance of membrane peel operations. Interestingly, robotic control over the procedure only appeared to aid performance over manual procedures when the OCT guidance was used.

References

  1. Yu, Haoran, Jin-Hui Shen, Rohan J. Shah, Nabil Simaan, and Karen M. Joos. “Evaluation of microsurgical tasks with OCT-guided and/or robot-assisted ophthalmic forceps.” Biomedical Optics Express 6, no. 2 (2015): 457-472.

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