Keeping an eye on the quick, precise and unique manufacturing of contact lenses

There are estimated to be 125m wearers of contact lenses worldwide in a sector that was reportedly worth $10.7bn in 2017.

The lens manufacturers expect demand to continue rising, with the sector anticipated to be valued at $17.64bn by the end of 2024. 

Lens makers must create huge numbers of disposable lenses, quickly and accurately. Here’s how it’s done. 

What’s involved in lens moulding?

The process starts with the injection moulding of a front and base curve mould. This mould is filled with a monomer (a molecule that can be bonded to other identical molecules to form a polymer) and is closed and cured before the lens is 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. So it’s essential that the moulds are repeatedly perfect too.

Are lens moulds produced in clean-room conditions?

Typically, yes, to mitigate cross-contamination. Any airborne contaminants, such as dust or 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 towards all-electric (90% to 10%). Repeatability is the main rationale, as well as meeting ISO Class 8 clean-room standards. 

Direct-drive machines offer a reduction of up to 75% in energy usage, and improved repeatability and cycle times. However, manufacturers of hydraulic machines have made big strides to standardise the process to accommodate the variations in moulds yet still meet quality requirements.

What other technology is used?

It’s critical that firms making contact lens moulds can do it repeatedly and with the highest precision in order to mass-produce them 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 a big role in maintaining cleanliness and efficiency, as each mould is typically produced in less than three seconds. Tasks undertaken by robots include unloading the mould tool and packing into sterile carriers. 

Are the lenses made on the same line?

Only one Sumitomo UK customer automates the entire lens production process. Packing and sealing the lens at the point of manufacture reduces the risk of contamination during moving.

But batch-making moulds and shipping to local markets where the lenses are produced offers greater flexibility. 

What does the future hold?

The next milestone could be smart lenses that monitor a user’s health through sensors and wireless technology. And the military is looking into the possibility of telescopic lenses that allow the eye to zoom.