DIGITEYES 2:

Part 2:

HOW?

What has been done so far?

Thank you to everyone who engaged with my last post! It has been fun to begin discussing this with you. Following up on your feedback I think we now have a good starting point to begin looking at some real-world attempts that incorporate digital tools into the existing workflow for making prosthetic eyes. If computer assisted methods are going to actually improve how we do things, they will need to do one or more of the following:

1) Improve the result: computer assisted methods allows us to make eyes that are in some way better than the hand-made ones.

2) Be more efficient: we are able to deliver our services more quickly, and perhaps less invasively

3) Increase access: patients who currently don’t have access to our services or who travel great distances, could get a prosthetic eye made for them more easily

Today I will be looking at some work that has already been done in this area. I will begin by focusing on one paper where a group of Belgian scientists try to innovate the impression method that we currently use to get the fitting shape.

2016 Belgian Paper: the critique of the impression

The first attempt to utilize digital technology to make a custom prosthetic eye that I am aware of is documented in a paper published in 2016.[1] The authors touted their “impression free” method: they replace the silicone impression that we are accustomed to using, with a CT scan of the socket. They suggest that the traditional impression calls for such an upgrade for two reasons: 1) the material introduces “errors” such as “soft tissue distortion,” and 2) it is time consuming. The authors are thus suggesting that replacing the impression with the scan both improves the result (by creating a more accurate model of the socket) and is more efficient (faster).

Having never worked with this method I cannot speak to whether or not it in fact produces better models. Still, I find this characterization of the impression method perplexing. When ocularists take an impression they customize an acrylic tray for the front curvature of the eye, and then add the silicone on the back of it. The silicone has a cream-like texture when it is inserted into the socket, and it flows and moulds into all the little nooks and crannies and textures in the orbit. Over the course of one minute, it solidifies to the consistency of a boiled egg white. It shapes itself to the socket, and not vice versa. A skilled ocularist knows how much impression material to use to optimize the shape that results.

If anything, one might argue that the acrylic impression tray could be said to “distort” the soft tissue, because it is rigid. But by this logic the prosthesis “distorts” the soft tissue too – that’s the point! The shape and resistance of the prosthesis forms the lids in such a way as to create symmetry with the extant eye. Ocularists utilize and build on this “forming” effect to perfect the naturalistic qualities of the prosthesis. So I do not understand why the authors are characterizing this effect on the soft tissues negatively as “distorting” rather than “forming.” Unless they are assuming that all of this is being done by an unskilled practitioner.

I also wonder whether their method is any faster, as I would imagine that to scan, digitally model the scan, and then print it, could only be as fast as the current methods if all of that equipment was located in one place. But private ocularists clinics are not in a position to invest in cone beam ct scanners, nor do most hospitals in Canada have 3d printers. In the traditional method there is usually less than 2 hours turnaround to process the shape that results from the impression.

Despite my scepticism about some of their claims, there are two things about their method that I find compelling. 1) this method is touchless. Some patients find the impression uncomfortable, and may prefer to have a scan taken instead. Maybe the CBCT scanner used in this paper is not the optimal scanning tool to use, but I am excited about the idea of some form of scanning coming into play for us to better serve those patients who find the sensation of the impression method intolerable, especially young children. 2) the authors have developed a method to digitally interpret and model the results of the scan, transforming the data they received from the machine into a fitting shape. In the right hands, this could be a valuable tool where the skills of the ocularist can be put to use in this new digital form.

So this first attempt leaves me optimistic that there is potential here. It’s hard to say yet whether this particular method is any better, but it just might be the start of something that will eventually become better.

[1] Ruiters S, Sun Y, de Jong S et al. Br J Ophthalmol 2016; 100:879-881