Making contact lens moulds - how do they do it?

Today, there are estimated to be 125 million global wearers of contact lenses in a sector that was reportedly worth $10.7 billion in 2017. The lens manufacturers, many of whom are based in Ireland, expect demand to continue rising, with the sector anticipated to be valued at $17.64 billion by the end of 2024.

Disposable lenses in particular are big business, with the soft lens segment share accounting for more than 80% of the overall market. Sumitomo (SHI) Demag is a major player in supplying the injection moulding machinery that produces the moulds that make these contact lenses. UK managing director of the company Nigel Flowers explains the process and the importance of precision and quality in lens moulding.

When was the first contact lens made?

It can be traced back to 1887 and German physiologist Adolf Flick. That lens was made of glass and was called a ‘scleral’ lens because it covered the scleral – the part of the eye that is white. Some years later, in 1912, optician Carl Zeiss developed another glass lens that fitted over the cornea. The first plastic lens (manufactured from plexiglass) is believed to be the work of two scientists, who created the scleral lens in 1938. The first plastic corneal lens arrived in 1948.

Among the issues, these lenses deprived the eye of oxygen and slipped out of the eye too easily. Over time, however, the diameter of the lenses reduced to improve wearability and, with the arrival of soft contact lenses (using hydrophilic gel), their popularity grew.

What’s involved in lens moulding?

The process starts with the injection moulding of a front and base curve mould. This mould is then filled with a monomer (a molecule that can be bonded to other identical molecules to form a polymer) and is then closed and cured before the lens is then hydrated and packed.

Every single mould used to make a contact lens is produced to a very high level of precision. Because the final lenses are moulded against a surface that has already been injection-moulded, any imperfection within the mould will find its way into the lens. The discarded moulds are recycled – but are not reused for moulding lenses.

Does this mean one mould for every lens?

Yes. Because no two eyes are the same, there are a broad spectrum of styles and parameters to meet when producing lenses. Every contact lens that is produced requires a bespoke mould. Each lens must meet the highest levels of quality and cleanliness. Therefore, it’s essential that the moulds are repeatedly perfect too.

Why so many optometric permutations?

A variety of moulds are used in the production of contact lenses, representing the different magnification levels (graded in quarter diopters) that are prescribed for each lens. The differences are in the variation in the space thickness between the front and rear of the mould, which dictates the thickness of the lens. There are a finite number of combinations and a standard number of magnifications and variations on the curve. Nevertheless, production still has to be carefully planned and controlled, to ensure the machines maintain the highest efficiency levels possible.

What are the latest advances?

In a relatively new development, bifocal lenses are now being manufactured on a larger scale to correct both near and far vision. With these lenses, the centre has a different magnification than the outer ring of the lens. In addition, some companies produce Toric lenses to correct astigmatism. These lenses are thicker or shaped at the bottom and sit on the tears on your eye, rotating into the right position within the eye. All of this places greater challenges of the machines to meet the specific needs of the customer. Breakthroughs are happening all the time. We’ve not quite reached the point where lenses are 3D printed according to someone’s eye, however this might be possible in the future.

Are lens moulds produced in cleanroom conditions?

Typically yes in order to mitigate cross contamination. While contact lens moulds are not technically classed as medical devices, any airborne contaminants, such as dust and particles from the raw materials, as well as human contaminants like bacteria, could affect the lens function.

For the production of lens moulds, both all-electric and hydraulic injection moulding machines are used – with the bias heavily weighted (90% to 10%) towards all-electric. Repeatability is the main rationale, as well as meeting ISO Class 8 clean room standards. Direct drive machines offer major improvements in efficiency, including a reduction of up to 75% in energy usage during operation and improved repeatability and cycle times. However, manufacturers of hydraulic IM machines have recently made big strides to standardise the process in order to accommodate the variations in moulds yet still meet the high quality requirements.

Moulders venturing into this specialist sector may also opt for a self-contained cleanroom moulding and packing system which are fully compliant with any GAMP and FDA requirements and have the required DQ, IQ and OQ documentation.

What other technology is used?

It’s critical that manufacturers specialising in making contact lens moulds can do it repeatedly and with the highest precision in order to mass-produce the moulds cost efficiently. Usually, there are between eight and 16 cavities in each moulding tool. To produce the lens moulds so fast without compromising on quality, Sumitomo (SHI) Demag installs its award-winning activeFlowBalance technology into the all-electric machines. This helps to combat the uneven filling of moulds by stopping the screw in the right place to allow the mould to fill naturally. This intervention reduces the cavity pressure and stress in the material. Once one cavity fills it moves on to another one.

Automation plays an equally big role in maintaining cleanliness and efficiency levels, as each mould is typically produced in less than three seconds. Tasks undertaken by these robots include unloading the mould tool and packing into sterile carriers.

Are the lenses manufactured on the same line?

Currently, only one Sumitomo (SHI) Demag UK customer automates the entire lens production process. Here, the company’s IntElect injection moulding machine forms just one small part of a huge production line whereby raw material is put in and, when it comes out the other end, the final product is packed and ready to ship. Packing and sealing the lens at the point of manufacture reduces the risk of contamination during moving and storage, however the complexity, investment costs and potential downtime issues are the downside to this approach.

Batch making the moulds and then shipping to local markets where the lenses are produced offers greater flexibility and operators have the ability to stop the injection moulding machine and compensate somewhere else in the system.

What does the future hold?

The Asia Pacific region was valued at over $2 billion in 2016, with changing lifestyles, eye health and cosmetic solutions driving demand. This region is expected to experience the fastest growth between now and 2024, with an estimated CAGR of more than 4%. The preference of disposable lenses – and relatively lower cost – makes them a much more appealing solution to resolving short or long sightedness than glasses.

Toric design lenses are also expected to report significant gains due to the increased demand to reduce corneal astigmatism. 

In an industry that is continually evolving, the next milestone could be smart lenses, which have the ability to monitor a user’s health through a series of circuits, sensors and wireless technology. The production of these lenses will be the same as existing products, but the capabilities will be even greater. Already, the military, for example, is looking into telescopic lenses that will allow the human eye to zoom.