Soft and hard contact lenses, how are they made?

The process of making contact lenses depends on several factors: are they soft or hard contact lenses, rigid gas-permeable contact lenses, or hybrid lenses?

How soft contact lenses are made

Soft contact lenses are made from a hydrophilic (“water-loving”) plastic polymer called hydrogel. These materials have the property of easily absorbing water and becoming soft and pliable without losing their specific optical qualities.

Soft contact lenses, including the new high-oxygen permeable varieties known as silicone hydrogel lenses, can be made in several ways.

One method uses a lathe cutting process, while another shapes the lenses by injecting the material. Both methods use state-of-the-art technology to quickly produce large quantities of lenses.

Lathe cutting process

In this method, non-hydrated discs (or ‘buttons’) of soft contact lens material are individually stacked on rotating shafts and shaped by cutting equipment whose precision is controlled by a computer with the greatest possible accuracy.

After the top and bottom surfaces of the lens have been shaped with the cutting equipment, the lens is removed from the lathe and hydrated to soften it. Once the lenses are fully finished, they undergo the necessary tests to guarantee optimum quality and performance.

This method of making soft lenses involves more steps and takes more time than the second method we will describe in a following paragraph, but over the years the process has become increasingly automated.

By using computers and industrial robotics, it now only takes a few minutes to make soft lenses using this method.

Shaping with an injection

In this process, the soft contact lens material is heated to a molten state and then injected under pressure into a computer-designed mold. The lenses are then rapidly cooled and removed from the mold.

The edges of the lenses are gently smoothed, and then the lenses are draped to soften them before undergoing a thorough quality and performance test.

In the meantime, most disposable contact lenses are made using this method because it is faster and less expensive than the lathe cutting procedure.

How gas permeable contact lenses are made

Most of these types of lenses (also known as RGP or GP lenses, short for Rigid Gas Permeable) are made from oxygen-permeable plastic polymer containing silicone and fluorine, among other things.

GP lenses contain very little water and remain rigid on the eye. This particular type of lens is custom made to optimally meet the specifications of the prescribing doctor.

It is therefore understandable that these types of lenses cost more than mass-produced soft lenses. A greater degree of customization is necessary with these types of lenses because they retain their shape and do not adapt to the eye like soft lenses do.

With this type of lens, even a minimal difference in the design of the lens can mean the difference between being able to wear the lens comfortably and the lens failing to function. It can also be painful and cause eye irritation.

Shipped dry to the prescribing doctor

The production of this type of lens relies on the lathe cutting process, which is, of course, computer-controlled. This method is very similar to the one used in the production of soft lenses manufactured by the lathe cutting process.

Usually, this type of lens is shipped dry to the prescribing doctor. In the doctor's office, these lenses are then soaked in a maintenance product specially developed for these lenses before being given to the patient.

This solution ensures that the surface of the lens provides the wearer with greater comfort when using the lenses.

Hybrid contact lenses have a central optical zone made of rigid & gas permeable plastic, surrounded by a peripheral fitting zone made of soft contact lens material.

Hybrid lenses are made through a process that is very similar to that of soft contact lenses made on the lathe. Yet there is a very striking difference: the plastic discs with which cutting is done on the lathe have a GP center, surrounded by non-hydrating material for soft contact lenses.

These two materials are brought together by means of the necessary bonding technology to prevent the materials from separating again after the lenses have been cut, ground and hydrated.