Abstract
Purpose :
To evaluate the tissue quality of a New Femtosecond (NFS) laser for refractive surgery. This study uses camera system to measure flap and lenticule extraction induced forward light scattering on retina. By comparing tissue quality and their scattering effects, one can optimize the NFS cutting parameters.
Methods :
To simulate forward light scattering effects on retina, various types of samples were used to create flap and lenticule extraction. First the location of the diffraction order from glass sample with flap cuts were measured by projecting its diffraction pattern from a laser diode on the wall with a fixed distance. Then the glass, gel, fresh porcine eye and live rabbit eye samples were measured with specially designed camera text fixture with white light to show the color dispersion rainbow effect from the laser cutting patterns. All the measurements were at fixed light level and optical aperture for comparison. By varying the laser cutting scanline steps from 2x2um, 1.5x1.5um, 1.2x1.2um to 1x1um on the NFS laser, the diffraction pattern on the retina changed and this helped to optimize the cutting algorithm and minimize the light scattering from surgery for NFS laser development.
Results :
Since NFS laser uses smaller laser beam spot size and smaller scanline steps, as compared to the on-market laser, the separation of the diffraction order increased as scanline step decreased. The first order diffraction pattern moved from retina fovea (on-marker FS laser) to the edge of parafovea (on NFS Laser). Therefore, the rainbow effect is further away from the fovea vision compared to the current FS laser system. The white light scattering measurements results on glass and gel samples showed the NFS laser new cutting algorithm with smaller scanline steps (1x1um) and less pulse energy used. This reduced the forward light scattering through glass samples compared to the current FS laser system (7x7um).
Conclusions :
The NFS laser standard flap cut shows significant improvement on flap induced scattering and better tissue quality with smaller spot size and beam separation. The measured diffraction order locations matched the optical ray tracing results on both NFS and current FS laser systems, concluding that the scattering effect will be less from NFS laser surgery vs. current on-market FS laser. The glare and halo effects will be minimized from NFS laser surgery.
This is a 2020 ARVO Annual Meeting abstract.