Largo, FL--Each year, U.S. doctors perform some 37,000 corneal transplants. Because sutures used in the conventional surgical technique can induce astigmatism, a sutureless method of implantation has been proposed. This procedure involves hand-cutting donor material to match a pre-cut aperture in the recipient eye. The circular aperture includes a series of thin, symmetrically-spaced pockets. These accept positioning tabs that extend radially from the donor blank's central portion.
"It was extremely difficult for doctors to manually prepare a tabbed corneal implant," says Joseph Collins of Tool Engineering. "The circle-to-circle fit from donor to recipient may leave gaps and/or bulges due to the donor material's elastic nature." Collins adds that because the implanted cornea is used as a transfer template to prepare the recipient eye, the operating room procedure is lengthy. This time spent in surgery increases expense as well as the chance of damaging the donor material.
Responding to a request from doctors at the University of South Florida, Collins invented and built a punch and die tool that precisely prepares a replacement cornea with symmetrical tabs. Punch shape corresponds to the donor blank's top surface. Likewise, the nest that receives the punch exhibits the same concave spherical radius.
To prepare the blank, the doctor aligns nest and punch, and places the donor material on the resulting surface. A vacuum holds the material in place. Lowering the die cuts the donor blank, with tabs, to its proper shape. The die descends until its upper surface is higher than the punch cutting edge by the required 100-micron (0.004-inch) tab thickness.
After producing the tabbed blank, the doctor lowers a guide tube onto the die's top surface. A round trephine within the tube cuts into the donor blank to produce a circular incision between the central portion of the blank and its radial tabs. Incision depth matches the desired tab thickness.
A tab thinning tool then cuts the tabs to size. The doctor simply places the slit donor blank on the tool's castellated nest. A syringe-vacuum holds it in place while the tab bender slides over the nest, forcing the tabs against the nest's outer wall. A second trephine slices off the tab's excess material leaving a properly prepared blank of consistent dimensions.
Additional details... Contact Joseph Collins, Tool Engineering, Box 2908, Largo, FL 34643, (813) 345-7959