Pupils are black holes

I’m not talking about students. I’m talking about that black hole in your eye. And that’s exactly what is it and it has nothing to do with astronomy, darn it. Thinking about that phrase, “looking deep into the eyes,” I actually do it as an optometrist but not in the figurative way. When you look at someone, try to look through their pupil. You can’t. I use a bright light (agreed?) and a pretty powerful lens to see through that pupil because what’s back there is even more interesting, your retina.

But back to the pupil. The human pupil has 2 muscles that make it work. How else could it move? There’s one that is circular around the pupil and then there’s the other muscles that are like spokes on a wheel pulling the pupil larger. And all day long there’s a fight between the two. Pulling (dilating) and constricting. Sympathetic vs parasympathetic for you physiologists. There’s even a name for that battle. It’s called hippus. Now when you’re close to someone, see if you can find that little battle in their pupil. Might be hard to do but it’s there.

I found out something new about Hippus that I didn’t know. This is for you eye doctors. Wikipedia says there is a pathological Hippus that can occur. I never knew that. It’s an increased amount of pupil battles, amplitudes, oscillations and occurs in a couple of different pathologies. And one of them is cirrhosis. But let’s not try to make any heads or tails of whether a person’s Hippus function is normal or not. I’m not even sure how to measure that honestly unless it was just completely obvious from what I normally notice and I rarely look for Hippus response.

Most of you know about squinting. You usually do that to reduce the sensation of bright light or glare but some people do it to see better. A small pupil helps vision. We don’t sell any drugs that you can take for that but there are side-effects of drugs that cause pupil constriction. If you squint to see better, what you’re doing is in some ways (all ways really) like how a pinhole camera works. You are only letting straight rays come in. Those straight rays don’t need glasses to focus them in the back of your eye.

On to a more curious thing about pupils and it has to do with other animals. Take a cat for example. That slit pupil is definitely weird. There are other animals that have the slit going horizontal. And then there are horses pupils. Those are horizontal and a bit rectangular. There are some other strange pupil shapes besides those as well. Wow! Nature is really crazy. Scientists seem to mostly reason that the variations in pupil designs help with the kind of optics these animals need to survive. Sounds reasonable to me. I wonder what it would be like to have cat pupils.




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