Active guidance for laser retinal surgery with a handheld instrument

Abstract

Laser photocoagulation is a standard interventional tool in vitreoretinal surgery. Commonly applied treatments such as grid photocoagulation and panretinal photocoagulation involve the application of hundreds of dot-like laser burns to the retina. In order to enhance the accuracy and reduce the tedium of this procedure, we are developing a robot-assisted technique for retinal laser photocoagulation that includes software for planning patterns of laser burns on a retinal image and uses an active handheld micromanipulator known as Micron in order to apply the pattern of burns to the retina. The paper describes the system and presents preliminary results. In a sample 7x7 pattern of lesions applied to an artificial surface, the system demonstrated a mean position error of 43+/-23 microm.

Fig. 1

The laser photocoagulation scanning system setup using Micron, an active handheld micromanipulator. Micron is shown held in the hand of the operator. The operator has the option of viewing the workspace either through the stereo operating microscope (at left) or on a 3D computer display (at right). The laser instrumentation is on the tabletop in the center.

Fig. 2

Close-up view of Micron in the hand of the user. The fiber-optic cable threads through the hollow center of the instrument, running down the actuated metal shaft of the tip. Four white LEDs act as optical trackers to provide micron-accurate positioning of Micron’s tip.

Fig. 3

The graphical user interface of the planning software, showing several of the types of patterns that can be generated. A photograph of the retina (in this case an artificial retina) is used as the background over which a preoperative plan can be made.

Fig. 4

Micron laser setup: Micron handle (a) attached to laser via fiber optic cable (b). Cameras (c) track the finder beam (d) and target (e) at 30Hz. Control velocity (f) is calculated in the image and converted to world coordinates used by the positioning sensor (g). The piezoelectric actuators then deflect the tip from position (h1) to (h2) to burn target (e).

Fig. 5

A sample 7×7 rectangular pattern generated with the system, with 650-µm spacing, on an artificial background (colored to simulate the retina). The automatically detected centroids of the laser burns are marked in red solid circles, and the planned targets are in hollow green circles.

Fig. 6

Histogram of dot placement errors, representing the distribution of distances between desired and actual burn locations.