Pig Eyes
While the world of ocular surgery training has changed since I was there, I can definitely remember how we used to practice surgery.
Occasionally, I used large unwieldy cow eyes, but the eyes I used most often, those that felt the most like human eyes, were pig eyes. In fact, there are still papers and studies published using pig eyes as a model for human eye surgery.
Though the moral implications of using animal eyes for surgical training are certainly worth discussing, it is definitely a historical fact that pig eye practice was a very valuable part of my early surgical career.