3D printing: manufacturing eye prostheses from plastic

Artificial eyes have been around for thousands of years – as indicated by those unearthed during excavations of ancient Egyptian and Roman burial sites. These were often made of gold, silver or clay, and served more decorative, aesthetic purposes.

In the 16th century, the first glass eyes were finally made to give the appearance of a real eye. This was initially only moderately successful, as the eyes could only stare fixedly. However, with the development of cryolite glass in the 19th century and the invention of the hollow glass eye at the beginning of the 20th century, both by the Müller-Uri glassmaking family, development really took off. For the first time, glass eyes looked confusingly like real eyes - and could move. From the Second World War onwards, the first plastic eye prostheses were manufactured in the USA. They also look very similar to their natural counterparts. And both fulfill the function of giving people who have lost an eye more self-confidence again and preserving the shape of the eye socket or face.

Modern plastic ocular prostheses are usually made of polymethyl methacrylate (PMMA). After taking an impression of the eye socket, they are mainly made by hand. The model cast from the impression is fitted with a lens, using the patient's healthy eye as a template. It is then milled and polished until everything shines. The advantage of plastic eyes is that they are virtually unbreakable and - unlike glass prostheses - can be worn by adults for several years if they are well cared for. To do this, they need to be taken to an ocularist once or twice a year and polished again.

Plastic ocular prostheses are particularly suitable for people who are restricted in their movement, for example, and where there is a risk that a glass prosthesis would break quickly. Children also benefit from plastic models for this reason. They are also perceived as more comfortable in cold temperatures.

Until now, eye prostheses made of medical plastic have been covered less often by health insurance companies than glass eyes, although the latter need to be replaced more frequently (annually). The cost of a plastic prosthesis has been significantly higher to date. However, this is now set to change. In the “Click2Print Artificial Eyes” (C2PAE) project, a German-British team wants to find a way to produce plastic eyes using scanners, software and 3D printers in a cost-effective and high-quality additive manufacturing process. The software, called “Cuttlefish:Eye”, enables the prostheses to be produced using 3D printing. Johann Reinhard from the Fraunhofer Institute for Computer Graphics Research IGD, deputy department head of the Competence Center 3D Printing Technology, explains in a press release from the German Federal Ministry of Education and Research (BMBF): “We can now digitally create eye prostheses using optical image data that we take of the patient with an OCT device and then manufacture them with a full-color 3D printer”. However, as OCT devices (optical coherence tomography) do not usually record colors, a camera and special lighting were installed especially for the project. This allows the software to send data to the 3D printer after the scan, which is sufficient to print a plastic eye with full color - i.e. with colored iris, pupil and blood vessels.

In addition to the visual appearance, which is of course an important factor for the wearer, the 3D-printed model offers another important advantage: the prosthesis adheres particularly well. Reinhard: “When a person loses an eye, a plastic or ceramic ball is implanted in the eye socket and the eye muscles are attached to it. The tissue is folded over this and the eye prosthesis is placed on top. There is still a certain amount of mobility between this tissue and the prosthesis, which allows the prosthesis to be moved. And adhesion is an important aspect here.”

So far, the patients fitted with the plastic prostheses have been satisfied. The researchers therefore hope that the software will soon be licensed in Europe, as it is in the UK. In future, the automation of production should mean that more patients can be fitted with a plastic prosthesis quickly and cost-effectively.