How Contact Lenses Are Made

How Contact Lenses Are Made

The history of the contact lens reaches back as far as Da Vinci, who sketched samples as early as 1508. The corneal contact lens was suggested later by the famed mathematician and philosopher Rene Descartes, in 1632.

But the modern contact lens really has its beginning around the turn of the 20th century. Adolf Fick gets the credit for inventing the first practical pair in 1887. But, it was Carl Zeiss, the famed lensmaker, who developed a glass contact lens that fit over the cornea that formed the prototype for all later work.

It was still to be several decades before Touhy invented the first plastic corneal lens, using Plexiglas as a material. In 1954 the keratometer was invented, making it possible to take eye measurements without physical contact, eliminating the need for molds from impressions of the eye. While work began in 1952, it wasn't until 1971 that the modern hydrophilic soft contact lenses came on the market.

That word, 'hydrophilic' (which means 'water loving'), is the key to contemporary contact lenses. Today's lenses are made of a plastic polymer (pHEMA) that allows the contact lens to absorb water. That makes it flexible and therefore comfortable.

Some lenses were formed in a molding process called spin-casting, where the plastic is spun into the desired shape. Today, injection molding is more common. Early methods required final shaping with a lathe, but today the process is so accurate the lenses can be made entirely through molding alone.

The lathe process may still be used in some areas of the world, though, especially for hard contact lenses that still make up anywhere up to 25% of those sold. The percentage varies by country. In this method a small circle called a blank is cut from a plastic rod and fastened onto a lathe with wax. It is spun rapidly and cut using a diamond or laser. The lens is then polished with a specially formulated abrasive.

The lens has to be finished to fit the patient's eye exactly. That's carried out by polishing the result into precise curves on both sides of the lens. Today, a computer controls the process, which is kept accurate by being fed information from the individual patient using data gathered during the eye examination.

The lens is then sterilized, often by being boiled in salt water for several hours, which also softens it. They're then packaged in a glass vial containing a sterile saline (salt water) solution. Because the lens material is hydrophilic it absorbs much of the solution, making it up to 75% water in the end. Because the solution is similar to human tears that moisturize the eye, the contact feels good and works well during use.

Research continues into finding materials that are longer lasting, more comfortable and safer to use. Some relatively recent advances, for example, include the Rigid Gas Permeable lens (RGP) invented in 1979, but marketed much later. They allow more oxygen to pass directly to the eye. That makes them more comfortable and safer to use over the long term.

Disposable lenses continue to advance, adding UV absorption to their attributes. Extended wear lenses, too, have improved in the past few years. Many can now be worn continuously for as long as a week to a month. On the leading edge are new implantable contact lenses that are actually placed into the eye and never require changing or cleaning.