Machine Design

Focusing on precision

A computer-controlled, motor-powered scalpel for laser eye surgery operates with micron precision.

The Carriazo-Pendular mini-scalpel cuts the cornea in one stage of Lasik surgery. The operation reshapes the cornea to correct nearsightedness and farsightedness.

It cuts a circular flap in a cornea with a consistent (10 to 12- m) thickness and smooth edges. To ensure blades in Carriazo-Pendular mini-scalpels are held securely, Schwind eye-tech-solutions GmbH, in Germany, selected a dimensionally stable, medical-grade polybutylene terephthalate polymer called Celanex PBT 2402 MT for the blade holder. The biocompatible PBT from Ticona, Florence, Ky., can be gamma-ray sterilized, resists wear and chemicals, and sports optimum slip-abrasion properties. It can also take the stresses imposed by the blade's pendular movement during cutting. The scalpel's spherical cutting head uses pendular movement to protect the corneal center and permits exact prediction of flap thickness.

"With the Carriazo-Pendular, we can cut flaps with better precision," explains Rolf Schwind, chief executive officer of Schwind eye-tech-solutions. The dimensional stability of Celanex PBT plays a key role, helping limit thickness deviations of the flap, depending on which cutting head is used.

Celanex PBT also has a high elastic modulus, absorbs little moisture, and is tough. Other qualities include good electrical properties, chemical and heat resistance, and little flash formation during processing.

Ticona, the engineering polymers business of Celanese Corp., (800) 833-4882,
Schwind eye-tech-solutions GmbH +49(0)6027-508-0,

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