Piezo-Based Precision Positioning for Corneal Refractive Eye Surgery

The first clinical studies investigating surgical methods to "shape" the cornea started in the 1930s – using mechanical micro-ceratoms or incisions with scalpels. Nowadays, ametropia can be corrected in a high diopter range – between +4 and -10 dpt – thanks to laser-pulse-based operation techniques. Several methods have become “gold standard” e.g. LASIK (Laser In Situ Keratomileusis), FLEX (Femtosecond Lenticule Extraction) and SMILE (Small Incision Lenticule Extraction). All of these methods have one basic principle in common: The shaping of the cornea in the optical axis by removing small particles from this highly-specialized type of skin. This treatment’s aim is to adapt the resulting refractive power of the cornea, eye lens and vitreous body to the length of the eyeball. And there is another decisive factor in common: Laser beam control and focusing requiring high-precision positioning systems.

Piezo-based motion and positioning systems are predestined for this application due to their high dynamics, unmatched precision and very compact dimensions.

For laser beam control, piezo-driven tip/tilt mirror systems not only offer the required accuracy but high accelerations and a great dynamic bandwidth of over 100 Hz as well. They are compact and can be integrated in higher-level systems, even in small spaces. They allow an optical deflection angle of up to 6°, extremely fast response behavior (10 ms to 1 ms with mirror) as well as position resolutions into the nanoradian range.

In the case of tip/tilt mirror systems with several motion axes, piezo drives are used in parallel-kinematics positioning systems. Unlike serial systems, there is only one moving platform with a common pivot point. Integrated high-resolution position sensors ensure linearity values of better than 0.25% over the full travel range and a repeatability of typically 5 µrad.

PILine® ultrasonic piezomotors are compact drives, capable of delivering linear and rotary motion which are characterized by high velocities and acceleration.