3D Printing of Prosthetic Eye

[mikemyers]

I am new to this forum, and also new to 3D printing. I am working with a group of people who want to be able to use a 3D printer to create a prosthetic (artificial) eye.

Is anyone else here involved in anything like this, or can someone suggest the best place to start a discussion? I've already got far more questions than answers, including:

• What are some good 3D printers for this application (small parts, but need to be very finely finished.
• What materials are best to print with - requirement that they are biocompatible
• Can the 3D printer also "paint" the eye as it is being constructed, so when the eye is finished, it will "look" like a real eye?
• If it can be "painted" (printed with color), will the resolution be similar to a 300 dpi ink jet printer, or much cruder?

In addition, I'm wondering how people "scan" the surface that a part, such as this prosthetic eye, will attach to. The eye will be mounted on "something" in the eye socket that moves up, down, right, left, etc., just as it used to move the real eye. This will be a mounting surface that the eye will attach to. Somehow that surface needs to be scanned, and the locating surface coded, such that the back end of the prosthetic eye will match up with that surface, including any mounting pins that may be there.


I am now in India, and the eye hospital I am working with wants to be able to provide inexpensive prosthetic eyes to people who could never afford a prosthetic eye made the old way. I found Altem, in India, who represent Stratasys. http://altem.com/3d-printing/ I'm hoping they may be able to provide what I need.

Any advice from you guys would be very much appreciated! Even if it only answers one part of all these questions, it will be very helpful.

[Feign]

Consider that a conventional prosthetic eye is simply a solid glass sphere, I don't think you have to worry too much about scanning or attachment points. Unless you want the eye to actually contain something (like a small camera, for instance) or have some unusual kind of form, you're better off just supplying traditional spherical glass eyes, but I'll go on to explain why.

To answer your questions in order though:
SLA and PolyJet printers make finely finished objects, other print types require post processing to make anything resembling a smooth surface.
Materials that are safe for internal use are a cornered market and sellers know it... In any kind of 3D printing medium. This is the biggest problem you'll run into for this kind of application.
SLA can only print one color at a time. Polyjet can print in multiple colors, but cost goes up sharply the more colors you can use.
It's possible to get around 600DPI, but again, PolyJet printers start out very expensive and as the resolution goes up, so too does the price.

Here is where it gets bad, Print material for Polyjet printers (Stratasys has a monopoly on the market) costs around $400 per cartridge, with the only biocompatible material (only available in one color being around $1000 per cartridge. Assuming an eye weighs 10 grams, that's $100USD to print one eye, and you can only do it in flat white. SLA can print for a bit cheaper, though I haven't found any reseller of biocompatible resin and even if I could, again it would be in only one color.

EDIT: Also, medical-quality SLA printers start at around $15,000 and go up. PolyJet printers start at around $18,000 new and multi-material polyjet printers are in the $40,000 to $90,000 range depending on quality. As the grade of PolyJet printer goes up, so does the price of material cartridges, with the biocompatible resin for the highest-quality Stratasys printers running $5000 for a 2kg cartridge... So that's $250 per eye, again flat white.

[mikemyers]

Consider that a conventional prosthetic eye is simply a solid glass sphere, I don't think you have to worry too much about scanning or attachment points. Unless you want the eye to actually contain something (like a small camera, for instance) or have some unusual kind of form.......

I'm still learning about these things, but apparently the reason the eye needs "attachment points" is because we want the artificial eye to move around just as the patient's other (real) eye moves. This part of it is fundamental. I think that the first things I need to look into is the mechanics of the eye, making an eye such that it mounts properly, and moves realistically. That means the "back" of the eye needs to match up with whatever we're using as an attachment point. ....which brings up the problem, how do we scan the eye socket, and use that data to program the 3D printer so that the eye will be made to fit that eye socket.

Let's leave the coloring of the eye until later. For now, let's assume that the eye will be hand painted.

You mentioned about $100 cost per eye. From what I've found so far, artificial eyes typically sell for $2000 to $8000 (http://health.costhelper.com/glass-eye.html). If we were using acrylic instead of glass, I suspect that should bring the $100 cost down considerably. The prosthetic eyes I was learning about today are made from "High Quality PMMA White Acrylic". Is this material is available for 3D printers? I did find what might be the right material to use, from a distributor of Stratasys in India, Altem. On their material listing page, http://altem.com/3d-printing/material-overview/ there are three types of material listed as biocompatible:
ABS-M30i “engineering plastic”
PC-ISO “stronger”
PPSF-PPSU “strong high performance plastic”

For example, detailed information on ABS-M30i:
http://altem.com/wp-content/themes/a...hures/M30i.pdf

I've got a lot of thinking to do. If we could find the right material, and print out a rough product, which just needed the final finishing, I think that would be a step in the right direction. It could be hand painted, and covered with a clear coating to protect it. What you've posted up above is likely to be a big help when we want to do this better, and print out a final product, but maybe we should start slowly.

If you could recommend a place where I can learn how to start with a physical surface we want to mate to, and convert that into data that the 3D printer can use, that might answer a lot of the things I'm puzzling over right now.

.....and the best thought I've come up with is to make a cast of the surface inside of the patient's eye, and from that cast somehow make the measurements that define the surface, in a format that the 3D printer understands.....

Thank you once again!!!!

[Feign]

Well, there's just the one "medical grade" material for the Stratasys printers, but I guess Non-toxic and Medical Grade are similar enough to be interchangable by India's medical standards (Sometimes the US regulations are a tad too much). It looks like it's possible to print PLLA Acrylic, though there isn't any data I could find quickly about the photoinitiator that it uses (this is often the most toxic part of a photoresin).

Oh, I looked again, all three of those materials are thermoplastics for the Stratasys Fortus machine. While the Fortus line is very good for FDM, it still has a rough finish and needs post-processing to get it smooth enough to simulate an eyeball.

Theoretically, it's possible to scan the back of an eye socket and extrapolate the rest of the measurements from there, but you don't want the prosthetic to be contoured to the back of the eye socket and I can tell you why. (Prepare for gory details, it's Halloween after all.) The Ocular Oblique and Ocular Rectus muscles connect at the front half of the eye. The back half, which "fits into" the socket itself is largely fluid and soft tissue that cushions and supports the loose ocular nerve. Spherical glass eyes do move slightly along with the existing eye due to friction with these partially attached muscles. If the back half of the eye were contoured to the back of the socket, the eye would be anchored in a forward position, with pulling from the ocular muscles pressing and digging at the socket constantly. If you can mate the eye to the front of the socket better, then that would allow it to move more realistically, though the user would likely need some kind of lubricant to keep it from irritating the rest of the socket.

[mikemyers]

I should be meeting with the doctors today or Monday who create this kind of prosthetic eye. I think I understand almost everything you wrote, but I'll know much more once I've actually seen the eye, and possibly watch the entire procedure of how they do this now.

My immediate project, is to take the prosthetic eye we are now creating manually, and create the same thing on a 3D printer. I'll have to ask one of the doctors here about how we avoid the potential problems you noted (I am in no way a doctor!!) :-)

As to the material, thanks for your feedback. I suggested we get one of the free samples, and see if we can use it in the 3D printer we already have.

Don't worry about "gory", as I've gotten very used to seeing things like this. I was thinking about posting images here of what we do, as it's happening, but I don't know the policy on this forum for images.

Earlier this morning, I entered a new thread here about measuring the surface. I thought I would keep the discussions separate. It was entered as a general question, not eye specific. Since you're referring to the eye, let me ask one question here:

......

Theoretically, it's possible to scan the back of an eye socket and extrapolate the rest of the measurements from there, but you don't want the prosthetic to be contoured to the back of the eye socket and I can tell you why. (Prepare for gory details, it's Halloween after all.) The Ocular Oblique and Ocular Rectus muscles connect at the front half of the eye. The back half, which "fits into" the socket itself is largely fluid and soft tissue that cushions and supports the loose ocular nerve. Spherical glass eyes do move slightly along with the existing eye due to friction with these partially attached muscles. If the back half of the eye were contoured to the back of the socket, the eye would be anchored in a forward position, with pulling from the ocular muscles pressing and digging at the socket constantly. If you can mate the eye to the front of the socket better, then that would allow it to move more realistically, though the user would likely need some kind of lubricant to keep it from irritating the rest of the socket.

Can you recommend a good source for me to learn about the "scanning". That's the data we need to get from the existing eye socket, and transfer to our 3D printer, but this is all new to me. I've been searching for appropriate links to that information, but haven't found a page that clearly explains how it is done.

Regarding your concern, I will print this out and ask the doctors here at the hospital about it. I'm sure they'll immediately understand, and tell me how they avoid those problems in the prosthetic eyes the already create.

P.S. - Again - is it appropriate to post photographs I've taken in this discussion?

[Feign]

Well, for what you want, the scanning option of choice would probably be some kind of very close-focussed photogrammetry, since you're dealing with a live subject. You'll need lots of small digital cameras, and a way to make them all take a picture at the same time, as well as a flash that preferably can have a colored grid or dot projection plate in front of it. Also you'll need software... And I'm not a software guy at all, but perhaps others will be able to help with that?

Current prosthesis gets around the rubbing issues by being a completely spherical smooth glass ball, the eye socket still provides fluid to lubricate it somewhat and avoid irritation, but then again currently, glass eyes don't move much.

I'm probably not the best judge of weather or not you can do that. I have a pretty strong stomach for medical photos (my parents really wanted me to be a doctor when I was young) but I'm pretty sure others here don't have quite so high a tolerance for it.

[mikemyers]

I can avoid working with, and inconveniencing, a "live subject" by making a cast of their existing eye, which is what we do now. That would give me a negative impression of the eye, which would be measurable. That's where I'm stuck - I would have the "part", which I know fits, but how to get that data into the 3D drawings, so it can be made.

prosthetic-eye-small.jpg

This shows what I am trying to make. I took the photo two days ago. The patient has what's called a "shrunken eye", and the prosthetic eye mounts over the existing eye. As the patient looks around, the prosthetic eye's movement matches the movement of the patient's real eye.

So where I'm at, is I need to get the 3D printer to create this part (can be made from high quality white acrylic), with the back surface fitting nicely over the patient's existing eye, and the front surface just the right amount outwards, so it matches the other eye. Polishing, painting, and so on can all be done later, and the entire part can be coated with clear acrylic, which then gets buffed and polished to a smooth, hard surface.


This shows what we do in making a mold, the mold that is created, and also a "positive" replica of the eye, made from the mold:

for-forum.jpg

I need a way to transfer the information from the back of the mold, into something the 3D software will understand.

[Feign]

Oh, okay, that's different than what I was thinking (and that's not a very common prosthesis at all in the US.) You definitely want to go with an SLA machine to print the blank and then paint it and polish it. If you're just scanning the cast of the eye, then you'll want a laser tomography style scanner. (turntable and laser 3D scanner, as it's sometimes called.) I think you'll find that most of the cost of these prostheses is in paying a professional artist to paint the iris exactly to match the person's other eye.

It may be possible to find a supplier of printable water transfer (AKA Hydro Dipping) film, the only one I've found is Pro Street Graphics, but as far as I can tell, they're America only. Water transfer is a good reliable method for putting a printed image on a physical object (mostly in America it's used to put camouflage or fake carbon fiber on everything for some strange reason) It's a very... temperamental process to print on this film (I've never gotten it to work personally) but if you can get it to work, you might be able to use it to put printed color-matched images of the iris on your print before coating with acrylic.

[mikemyers]

After a lot of reading, I am now thinking that the Stratasys Mojo Desktop 3D Printer would be a good starting point, both from having a very good reputation, and a nearby distributor for support, but also for making what seems like an ideal 3D printer:

https://www.youtube.com/watch?v=cibbsqME1Pw

Instead of having to learn all about setting up and working with a 3D printer, we would instead just be learning how to print the parts. To me, this video looks as if one is purchasing a regular 2D printer - you just put in the paper, and print - and expect that all the prints will come out perfect. The more I watched the above video, the more impressed I was. It is a fully developed system, that just works.


Regarding making the prosthetic eyes, we do all the work you refer to right now (casting, painting, sealing). We make several casts, and eventually end up with the white acrylic part, which is painted and then covered with the clear acrylic. It takes a lot of time, but the end result is very good. We have some kind of 3D printer that was used for other purposes, but the parts it made seemed very crude. The Stratasys by comparison seems to be able to print perfect parts, that require very little extra finishing.

We also want to be able to create the prosthetic eyes you are familiar with, that are used when a patient has an empty eye socket. I have a meeting in a few days with a doctor who specializes in this, so I can learn more about what's involved.

...... If you're just scanning the cast of the eye, then you'll want a laser tomography style scanner. (turntable and laser 3D scanner, as it's sometimes called.) ......

THAT is exactly what I need to learn about. What you just wrote is the first time I've ever seen that. I know we need a way of getting the data from the mating surface into our computer, so we can define the printed surface, but until now, I haven't found anything to put me on the right track in searching for the information on HOW to do this. I'll start by searching for the words you used - if you can suggest a good website that explains this, that would be a huge help. In the meantime, at least I have something to work from.

[JamesFromBywong]

When the eye is removed (enucleation), it is replaced by a coral ball about 25mm in diameter to which the muscles that move the eye are attached. The skin (I think from the back of the eye) is pulled to the front and sewn over the coral ball.

The prosthesis fits over the skin covering the coral ball and moves with it.

The prosthesis is made by taking a mould of the socket using a paste in the same way that moulds were made for false teeth. A wax model is then made and fitted so that the eyelid closes and the eye bulges in the normal way. The coloured part is painted by hand on a small round piece of (I think) acrylic.

The final prosthesis is made from acrylic by (I think) moulding.

Considering the above, I am not sure that 3d printing would provide a simpler or cheaper solution to the problem. The art is in painting the eye and in the fitting.

Just my $0.2