When you want to know how contact lenses are made this article is for you. In this article, you will in-depth information on the manufacturing processes as well as the steps that it takes to make contact lenses from the measurements up to the point where the contact lens sits on the eyes of the customer.
There are four common ways how contact lenses are made. Those processes are:
- Spin casting
- Lathe cutting
- Cast molding
- Reverse Process III (RP III)
- 3D Printing
When contact lenses need to be made the optician performs the measurements and sends those to the lap to produce the lens. Those measurements deliver the information to the manufacturer of the lenses on how the eyes are shaped. In most cases today a topographer will be used for those purposes. However, in very complicated cases, a testing lens needs to be applied first to see what lens geometry will fit the eyes best.
Those processes have been around for decades to make contact lenses. New in these fields is custom molds you can see at the end of the article which will be then scanned to produce 3D printed lenses. But those lenses are only used in very rare cases.
Contact lenses made with spin-casting start as a liquid polymer. This liquid polymer is injected into a spinning mold. When the mold spins centripetal force forms the curvature of the contact lens. The anterior part of the contact lens is directly made by the curvature of the mold. After the monomer reached the desired shape ultraviolet light is applied to harden the material in the mold.
Afterward in the finishing the back surface is polished to produce smooth edges for comfortable wearing.
Advantages of spin casting
- Very good reproducibility
Disadvantages of spin casting
- Depending on the contact lens design increased spherical aberration is possible
With lathe cutting a rigid base material called button with a thickness of 4.5mm and a diameter of 12-15mm. Out of this buttons a spinning machine grounds the button to the desired diameter of the lenses the optician ordered. In the following manufacturing processes, the base curve gets cut as well as the peripheral curves.
During this cutting process, the button gets thinner up to a point of approximately 2.5mm in the center of the button. After the cutting process, the semi-finished buttons will be polished for less than 50 seconds with an abrasive paste. Afterward, the button will be cleaned in an ultrasonic bath before the anterior surface can be cut.
Therefore the button gets blocked with wax to a curvature tool which matches the surface made before. This process can seen on the thumbnail of the video below. When the back surface was cut the bearing surface of the lens was cut. Depending on the needed prescription the front surface will be flatter or steeper.
For high prescriptions, the front surface can have multiple anterior curves. This way the lenses will be manipulated less by the lids of the eye. After cutting the anterior surface the contact lens will be finished after the surface gets polished. Then saline is applied to the lens and it gets stored in a blister and packaged for the end consumer.
Advantages of lathe cutting:
- Established technology
- Wide range of parameters available
- Compatible with most materials
Disadvantages of lathe cutting
- Labor intensive
- High cost per lens due to longer production times
When contact lenses are made with cast molding a liquid monomer is injected into the anterior mold. The anterior mold is also the anterior surface of the contact lens. The liquid monomer then gets distributed in the mold with a little pressure from the posterior mold.
With the back and front surface, the whole shape of the contact lens is already made. But the liquid monomer needs to be hardened. This is why UV light shines on the monomer to produce a material that can be then put on your eye.
Advantages of cast molding:
- Low cost per lens
- Low production time
- Great surface quality
Disadvantages of cast molding:
- Not all materials are compatible with cast molding
- Ideal for stock lenses only
Reverse Process III (RPIII)
The reverse process III combines the best of spin casting and lathe cutting to produce contacts. With this combination of methods, the anterior surface of the lens is made with spun cast and the posterior surface is made with the lathe cut method.
Here in the video above you can see some insides from the manufacturer of soft contact lenses Johnson&Johnson. As you can see when It comes to producing conventional contacts the processes are extremely automated.
In very complicated cases contact lenses can be made with a highly specialized 3D printer. The company Eyeprintpro is able to manufacture contacts for people that can not be successfully fitted with traditionally manufactured contacts.
In the paragraphs above I mentioned the optician starts with topography to gather the data for the contact lens. But this approach (depending on the topographer) measures only a part of the surface of the cornea. In complicated cases where abnormalities hinder a normal contact lens from the optimal fitting the measured surface area needs to be increased.
They are able to measure a bigger surface with a custom mold from the eye. When this mold is hardened after a couple of minutes the optometrist or optician then sends it to EyePrintPRO where a 3D scanner scans the mold. Then the lab has the exact data of how the eye is shaped. This way the custom lens can be made that sits on the white part of the eye does not touch the cornea and has a liquid reservoir between the lens and the back surface of the contact lens.
Here in the video below you can see how the process looks like until this highly custom contact lens is made.
Now you know how contact lenses are made and what various methods can be used to produce them. When it comes to the production methods they all have their special use cases. With some of them, the manufacturer is able to make a highly custom design while with other manufacturing methods really low production times and therefore lower prices can be achieved.
I hope you found the information about how contact lenses are made.
I wish you a great day.