Pupils are black holes

Pupils are black holes 0

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.



Enhanced by Zemanta
Blonde fundus

Blonde fundus 0

I can’t figure out why this phrase even occurred….blonde fundus. I was looking up some other eye things this morning and where the words originated, like Greek or Latin derivations, and wanted to write about this one condition called amaurosis fugax but decided it’s just a bad problem that needed too much of my brain power. So I decided to look up some other things and settled on how we doctors might describe how a retina looks. Usually I just tell a patient that the back of their eye (their retina) was normal and healthy. But for some reason I was taught a special way to describe the appearance of a patient’s retina…probably because I should know that the variations in the appearance of a human retina can vary significantly. So to simply explain what a blonde fundus is, check the color of your hair. If it’s naturally blonde, or long ago it was :), then your retina probably is blonde. But the retina is not really blonde. It just has less pigment in it like your hair. I wish I could say for sure if the two were related to specific genes and I’d bet so.

There are some different layer structures in the retina where you find certain types of cells. You know, rods and cones and stuff. Well there’s a couple of other layers back there called the choroid (pronounced core-oid) and retinal pigment epithelium. I don’t know why there’s epithelium deep in the eye. I always thought epithelium was my skin. Maybe schools teach what our outer skin cells are called first and that just made me not understand what epithelium really is. Whatever the reason, these retinal layers in the eye contain melanin. A smaller amount of melanin means the retina looks redder. Look at the pictures I included below. And yep, in case you wondered, those pictures of red eyes from photographs are showing you, generally, who has the blonde fundus (or plural – fundi). The angle of light has to be just right though to get that red eye effect. Since the red eyes in pictures, or more specifically, the red pupils are the result of the redder color in the retina (red comes from blood) we see this effect reflecting from the camera flash back out of the eye.

Anyway, if your doctor says you have a blonde fundus you’re ok. But if the doctor doesn’t say it, you’re still ok. It’s just something we learned in school so we can call your retina names! Here’s one more name, tigroid fundus. You’re ok if you have that too! Oh, the word fundus is used to describe the bottom or end part of an organ so it’s not just an eye word. Maybe instead of saying bottoms up when we finish our bottled beer we could say fundus up?

blonde fundus

blonde fundus

dark fundus
dark fundus

tigroid fundus
tigroid fundus