These tiny pieces of soft plastic are made with such a high degree of precision to fit your eye to provide the correction it needs, that one might wonder, “How are we able to create a perfect little lens that sits on your eye and helps you see as though you had 20/20 vision?”
While the answer is not as sought after as the Caramilk secret, the “but how is it made?” question rarely comes up with our patients, so we thought: let’s tell them anyway. It’s interesting, plus, it’s a fun topic of conversation around the dinner table. So here we go, these are the two main processes used to make contact lenses:
Lathe Cutting
Once your Optometrist has determined your prescription, as well as the diameter and the curvature of your cornea, the data is sent to the contact lens manufacturer that will be making your lenses. That data is entered into a computer that will control all of the machines used during the process.
With lathe cutting, a cylinder of contact lens material (typically hydrogel, with or without silicone) is inserted in a machine that will rotate incredibly fast. At this stage, the material is still dry and hard. A diamond grinder will cut the proper diameter for your lenses and will carve the inside of the lens to fit your cornea. This piece of material will then be glued to a piece a metal so it can be mounted on a second grinding machine, which will precisely cut the outside curvature of the lens. The glue is removed, the quality of the lenses is then tested, and the dry pieces are hydrated, expanding them to their full size, and finally, they are packaged.
This really interesting episode from the show “How it’s Made” will show you the detailed process better than we could ever describe it in words!
Video to embed:
https://www.youtube.com/watch?v=oJeKr6wJXiQ&ab_channel=HowIt%27sMadeShow
Injection Moulding
This technique, which is mostly used for disposable contact lenses, consists of heating the contact lens material until it is melted and injecting it in a cavity fitting the exact measurements sent by your Optometrist. Some manufacturers use a material that is already liquid and then use UV light to set the hydrogel. The mold is then disassembled and the lens is washed and tested to ensure its quality. It is then packaged and sent to you! This method is usually faster and more cost-effective than the lathe cutting method. But it’s not ideal for Rigid Gas Permeable lenses, which is why these are made using the first method.
And there you go, perfect contact lenses made specifically for your eyes! Depending on the manufacturer, different technologies are integrated into the lens material. For example, Acuvue makes photochromic contact lenses that become darker when exposed to UV rays. How cool is that! Companies can also make coloured contact lenses and contact lenses for every type of refractive error that you may have, even astigmatism!
