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Precision Vision

New Zealand Computer Scene - June 1989

by Brenda Lobb

Right here in New Zealand we have the most advanced machinery - the Rolls Royce of the industry - for making contact lenses. Computer aided design and manufacture makes possible production of lenses of unprecedented accuracy.

CAD systems enable lenses to be designed in a fraction of the time taken by manual design, says Hirstlens Divisional Manager, Ian Handricks, and custom-built computer-controlled machinery gives accuracy to the micron level in lens production.

Contact lens manufacture has been a cottage industry; lenses were designed and made by hand, by traditional, rather than "Mickey Mouse" methods, says Handricks. "To design a lens, you had to make one, break it in half to get a cross section and then manually measure its thickness at various points across the lens. Then to draw one, you had to get a five or six metre length of string, weight it with a pencil and swing it to get an idea of the changes in arc."

More Accurate Design and Manufacture . . . Using CAD, Handricks has written programs which, when radius and diameter pairs are keyed in, draws a finished lens arc, accurate to many decimal places.

It is no longer necessary to manufacture a lens to do the metrology necessary for production. And together with an international team including other New Zealanders, he has designed and built computer-controlled equipment to make lenses. "We are the only manufacturers in the Southern V Hemisphere who have this fast, accurate technology", claims Handricks. … in Less Time

Contact lenses are made from little plastic buttons which are cut, shaped and then polished to fit the cornea of the eye. The cornea is not a symmetrical spherical shape but is an elliptical shape which can be matched only by a lathe cutting off-centre so that the resulting lens exactly fits the cornea.

This is a complex process, done in several stages. It takes skilled staff four or five years to learn to make a lens by hand, says Handricks and production is necessarily painstaking. But with computerised equipment it takes only six minutes to cut a lens. Old Hardware, the Latest Technology

Most of Hirstlens’ soft lenses are now made on two new computerised systems, called Polytech 2000 - by one skilled operator, where it took ten before. The system uses quite archaic technology: a Z80-based computer running under the CPM operating system and using an 8 " floppy disk drive, the Polytech 2000 has home-made motherboards and some 80,000 lines of Turbo Pascal code to control the lathe. It automatically generates exact and repeatable peripheral curves, sets the positions of the lathe and senses the beginning and the end of the lens; the blocking method has been patented world-wide, says Handricks. The system produces a very polished finish, although Hirstlens hand-polish every lens at the end as well.

Because the method is clean and uses no heat, there is no damage to the surface of the button, and it’s economical: "We get 50,000 passes out of a single cutting tool. We’d be lucky to get 3000 out of a manual cutting tool," says Handricks. The equipment takes up much less space on the factory floor than the many stages and staff of a manual system, too. Prescription details are stored for reproduction, and odd or unusual prescriptions are handled as easily as regular prescriptions. The computer screen shows the machine status at all times. It’s much easier to learn than the old manual methods, says Handricks.

Computer aided design and manufacture has ushered the art of making contact lenses into the 1990s - and perhaps frees vision technologists to pursue further exciting ideas. Watch this space!

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