Personally, if I have the time I'd probably make a medium sized model made of paper mache and other materials of varying colours to accurate indicate the nature and parts of the eye e.g. The choroid may use a black shoe lace going around the paper mache eye at the back. Alternatively, you could try to develop a 3D model on software but I don't think it's that easy...
get a balloon blow it up to desired size.
then get stripped newspaper and soak it in glue
paper mache' the balloon
let it dry etc...
then paint it
and add details
done.