This accessory for your lens helps your model getting comfortable looking at the lens. It is made for 30mm googly eyes and fits my 77mm B+W UV filter. The inside diameter is 79,30mm to compensate a little for printing tolerances. It fits nice and tight and makes the shoots just a little more fun!

I have printed it in PLA, but I reckon PETG would be even better due to it being a little more flexible. 

If you want to customize it to your lens diameter, there is a Fusion 360 file which has a variable to set the diameter of the inner circle.