What is the very hard sphere inside the eye of many common fish made of and how is it called?

Question

Inside the eye of many common fish, like tuna, scad, snapper, actually probably all fish I have eaten, is a small sphere made of some very tough substance. This sphere is even hard to crush with teeth, and seems to be made of homogeneous material. That is after the fish is cooked, not sure how it is uncooked. It is immersed inside a quite soft, almost liquid substance inside the eyeball.
Is that the lens, or is the whole soft semi-liquid tissue the lens?
What substance is the small tough sphere made of? I imagine some type of proteins, but what type of proteins exactly?

Adhish · Answer

From what you describe, it seems the hard sphere is the lens and the semi-liquid substance is the vitreous humour. Like the lens of other vertebrates, the fish lens is made of lens fibres—cells rich in proteins called crystallins.
For more on the anatomy of fish eyes, you could read this page and watch this dissection video.

What is the very hard sphere inside the eye of many common fish made of and how is it called?

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