I've made many puppets with ping pong ball eyes - painting them myself or asking an artist friend to paint them. That worked fine for static eyes - using them for animatronics was more difficult (I had made some 3d-printed parts that can be glued to the eye to make it movable, but the mechanism and eye are fragile).
Last year I got some puppet eyes made of resin - they were not the right size, but they gave me an idea: 3d-print the white part of the eye, paint it and fill the iris and pupil with transparent resin. That would be more sturdy when a ping pong ball.

I made a new 3d-printable eye model (that is lightweight, has a lever in the back, space for an LED inside and takes up minimum space) and bought an Elegoo Mars UV resin printer (the model was made to fit in my model for 3d-printed movable eyelids). This is my first completed prototype:

I printed the eye with white UV resin and painted the eye with white spray paint (I wanted it more glossy) and acrylic markers. 
Comments
By Shawn on Jan 13, 2020, 3:48 PM
Really nice! So the iris, is also done on a 3d printer of sorts?  Had never heard  of a resin printer. I am off to google to learn more.
By Tioh on Jan 14, 2020, 6:29 AM
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The Elegoo Mars is a DLP 3D printer. It's built around a resin tank with a transparent bottom and a build platform that descends into a resin tank to create parts upside down, layer by layer. The resin is UV active, a UV light sits in the bottom of the machine with a digital display (basically a high-resolution display like it is used in a mobile phone - without the backlight) in between. That display works as a shutter - controlling where the UV light can reach the resin. 

On this digital projector screen, an image is displayed of a layer across the entire platform, curing all points simultaneously. 
There are many types of UV resins available - most are very toxic (and also smell like superglue) until cured. You need a well-ventilated room and have to make sure that children and animals cannot come into contact with the uncured resin.
By Shawn on Jan 14, 2020, 9:07 AM
Gee should have just waited for your explanation.  Better then some I found on-line.

So it is the iris itself that is resin printed, right? Then I assume you hand paint the color on the back. Would a pre-made off the shelf iris work with your eye model for those that don't have a resin printer?
By Tioh on Jan 14, 2020, 1:17 PM
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Pupil and iris are indents in the eye model. I made the shape of the iris by subtracting a ball from the eye - the pupil was made by subtracting a disc. That gives it a slight 3d-effect (looks like the pupil is aimed at the viewer). I use 2 component resin to fill the indent after painting - that part is not 3d-printed. The iris has a 16.5mm diameter - I doubt any premade would fit, but I could make another model for that purpose,

The eye can be printed with a normal filament printer too - it's just more work if you want to hide the layer lines by sanding the object. 
By Shawn on Jan 15, 2020, 12:41 PM
Got It!   After I posted I was looking closer at the images and was wondering if that was the case.  I assume that by printing the eye ball in resin that if you light it from behind that  you get a better result also. 

I myself have not done much with 3d printing but my house mate is a set designer and uses it for making furniture and elements for their 1/4 scale models. The only big challenge is at that scale you can't get much detail.
By Tioh on Apr 13, 2020, 11:23 AM
I released my 3d-models for the movable eyes and eyelids on Thingiverse.
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https://www.thingiverse.com/thing:4282985
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Discussion Started Jan 13, 2020 By
mailhit
Tioh
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