Well yes, but also no.

The term pupil is used to describe an area that exists inside a three dimensional space, the eye, and while that space may not have anything that reflects light, it_does_contain something. The surface of the eye, known as the lens, and the liquid or 'jelly' that is contained inside the eye. So that area that is light reflective material would include the whites and the iris, but the inside of the eye is not just empty space. If it was, your eye would collapse like an uninflated beach ball, and you wouldn't see very much at all. Arguably the term pupil is used to refer to the non-reflective area of the eye bordered by the iris and containing the lens.

Eye sphincter sounds weird though.

Oh boy. Don’t look too deep into philosophy of language, or you might become convinced that “the iris” is just as nonexistent — or that all nouns are really about a symbolic existence as a relationship, for which measurable physical matter is inconsequential.

I mean we have lots of words for varying degrees and styles of "nothing".

A chasm is the empty space between two chunks of the earths crust.

A void is just an empty space well... Void of all things.

An interval is just the time between two events. Technically it's nothing.

Still a good shower thought. There aren't a ton of words dedicated to the same phenomenon, but we have a handful.

This is a great point! Humans can put names on things that aren't there, such as holes!

This 'naming of hole-like concepts' may sound trivial, but there have been entire cultures that didn't have 'hole-like' concepts and this stunted their ability to make certain discoveries. For example, the ancient Greeks could not have developed calculus; they did not have a concept of zero that they could use for mathematical manipulation. This shows an unfortunate reality: you can't mentally manipulate ideas that you don't have.

However, once you do have those ideas, they may seem obvious. This is a well documented human bias: the curse of knowledge. Once you understand something, it is very difficult to imagine not knowing that. For us, knowers of pupils, holes, zeros, and chasms, it may seem absurd to not have names for pupils, holes, zeros, and chasms. We take them for granted, when in reality it was not an easy road to arrive at them.

Could it not be said that "nothing" is actually a thing? 🤔

A hole is a thing.

Same situation with assholes and anal sphincters.

Never call someone a massive asshole, call them massless.

Wait until I tell you about this weird concept, the zero…

I'd say it's more than just a hole. I had an eye injury when I was a teenager that caused a detached iris. I didn't have a massive pupil, I had 2 small, irregularly shaped pupils. After surgery, I now have a permanently dilated pupil shaped like a teardrop