Intraoperative wavefront monitoring during laser thermal keratoplasty

Low energy laser thermal keratoplasty (LTK) is being proposed as an alternative to conventional holmium LTK in an effort to minimize corneal tissue necrosis, regression, and induced astigmatism. Real-time wavefront monitoring during surgery is also being proposed as a method for regulating induced aberrations and the treatment end point. We evaluated the feasibility of intraoperative wavefront monitoring during low energy LTK.

An investigational prototype system combining a Sunrise Hyperion laser with a Shack-Hartmann wavefront sensor (Wavefront Sciences COAS) was used to treat 20 hyperopic eyes with a low energy application of eight spots of 18mJ/shot (144mJ/pulse) at 5 Hz in two rings of 6 mm and 7-mm diameter, while monitoring the treatment with real-time dynamic wavefront sensing up to 10 captures/second of 4th order Zernike data.

The integrated wavefront-monitored LTK unit showed good stability in measuring dynamic intraoperative wavefront refractions before, during, and after the low energy LTK treatment. The readings did not interfere with the application of holmium laser pulses, nor did the LTK treatment distort the captured wavefront readings. A steady improvement of the wavefront-derived spherical equivalent refraction followed the laser treatment pattern, with a mean attempted spherical equivalent refractive change of 1.66 D and mean achieved change of 1.71 D.

Intraoperative wavefront monitoring was feasible during low energy LTK. With future adaptation, it might be possible to dynamically relay the captured wavefront information to the laser during ongoing treatment, to intraoperatively control the surgical endpoint for multiple aberration terms.