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Handheld flexible robot with concentric tubes aiming for intraocular procedures 157

6.2.4 Challenges in intraocular concentric tube robot design

6.2.4.1 Dimensions of current concentric tube robots
Due to the different use cases for current CTRs, the overall dimensions of these devices
tend to be quite large. The handheld steerable needle [23] is a close fit for the requirements
of eye surgery. For a CTR to be useful for eye surgery, the robot’s dimensions must be
within the vicinity of current eye surgery tools, to interfere as little as possible with the
workspace visibility of the surgeon.

6.2.4.2 Tube specifications

The tube dimensions should be comparable to that of current surgical instruments used.
Therefore the tubes should be within the 25- to 20-gauge (0.5 1.0 mm) range.

6.2.4.3 Portability
As a device for light pipe steering, the device should ideally be small enough to be
handheld in a similar fashion to current commercially available light pipes (10 20 mm).
However, with the inclusion of actuators, a more realistic diameter that is still viable for the
handheld operation would be in the range of 33 mm [25,26].

In addition, most of the CTRs reviewed had the motors placed at the rear side away from
the end-effectors. Having the weight distributed evenly, or concentrated near the supporting
axis, that is, near where the device is to be held, would aid in its ease of use.

6.3 Intraocular concentric tube robot prototype design

6.3.1 Workspace requirements

For the purposes of defining the workspace, we will assume an inner diameter of 26 mm in
the proof-of-concept design, according to the normal human retina to retina distance. To
meet the challenges mentioned earlier, there are a few parameters that must be defined: the
number of tubes, tube diameter(s), length(s), and curvature(s).

6.3.2 Tubes

Most light pipes are composed of a single tube. This means that the surgeon must rotate the
light pipe about the entry point to adjust the angle of illumination. Directional laser probes,
on the other hand, include two tubes, with the inner tube being precurved. This allows laser
probes to enter straight while supplying a greater range of motion when working on the
periphery of the eye. Like directional laser probes, the CTR will use two tubes, with