A digital workflow for 3D printed full-colour ocular prosthetics

Abstract

Fabricating custom-made ocular prostheses is currently a highly-skilled, labour-intense and non-reproducible process performed by an ocularist. Custom-fit prostheses are made from acrylic using a plaster mould, the iris is hand-painted, and veins are mimicked by adding red embroidery threads. Digital production techniques provide opportunities to improve and automate this process. Therefore, this graduation project aims to research a possible digital workflow, including data capturing and calibration, modelling and 3D printing, for producing 3D-printed full-colour ocular prosthetics. The workflow should capture and reproduce the eye’s appearance to create a life-like ocular prosthesis that resembles the patient’s facial appearance as closely as possible.

Research into manual and digital production techniques results in a proposed digital workflow showing how a prosthesis can be produced. The workflow consists of five phases: collect, design, produce, post-process and finalise and shows how the patient and the ocularist are involved.

Data capturing and calibration
The patient’s eye colour data needs to be captured and calibrated to ensure accurate colour reproduction of the eye. The images can be calibrated by applying a colour profile made from a colour target to correct the camera error. The capturing research showed that photographing is a suitable technique to collect colour data for accurate colour reproduction if the eye and the colour target are shot under a controlled light condition. Multiple calibrated iris images were printed and compared to the participant’s eye to review the capturing and calibration process.

Modelling
The modelling research showed that a parametric model based on a computational design template is a suitable solution for adjusting the prosthesis model to a personalised shape.
The template should automatically model the inner parts of the prosthesis based on the outer shape and important parameters, such as the iris and pupil diameter. The first steps towards creating this computational design template are shown in this report by modelling a parametric iris disk.

3D Printing
The full-colour 3D printing technology's capabilities were exploited to reproduce best the various features of a human eye, such as the sclera, blood vessels, pupil, cornea and iris. This investigation showed that mapping an eye image to the model does not always give the desired result and that different printing techniques are suitable for different eye parts. Alternative approaches, like contoning, sclera generator and ‘dotting’ and ‘varying line deepness’ techniques, are exploited and show promising results. However, a voxel-based printing technique is needed to combine and control these approaches, and current software lacks these possibilities.

Two experts and five users validated prostheses produced following the proposed digital workflow through an interview and by photographing them next to their eyes. All participants were impressed by the prosthesis and rated the total prosthesis as ‘sufficient’ or ‘good’. Nonetheless, it remains a challenge to reproduce the exact iris colour, structure and veins. A voxel-based printing technique is recommended to have more control over these various aspects. More research is needed to explore the possibilities for controlling colour on a voxel level and to model a complete voxel-based prosthesis. The comparison between the manual and digital workflow showed that 3D printing results in significant time savings since over four hours of manual work could be replaced by 3D printing. 3D printing ocular prostheses make the workflow reproducible and faster, which leads to more accessible and affordable prostheses in the future.