The metaphysics of dilation

The metaphysics of dilation 0

Because I am an optometrist I dilate. Or is it because I dilate I am therefore an optometrist? In either case I am allowed, by law in Colorado, to use diagnostic pharmaceutical agents in the course of a patient examination in order to enlarge pupils. I’ve recently come to find out that there’s a wide range of the use of these drugs by others in my profession. My debate over the purpose of routine use of these diagnostics was made clear to me after 16 pages of discussion but ended more in how often a patient should be seen for a regular eye exam than how often a patient should be dilated.

First, the drugs. Dilating can be done with different chemicals. There are kinds that vaguely dilate pupils and others that can maximally dilate your pupils for a week or more. Why would one doctor use one drop and another doctor choose the stronger or weaker one? That, my friends, is based on your doctors training and beliefs or needs. You see, doctors are people. There isn’t one way to do things so we pick the way we personally want it done. And that’s ok. Here are a few types of dilating drops if you want to look them up: tropicamide, paremyd, phenylephrine (also found in some OTC redness relievers), homatropine, cyclopentolate and atropine. And most of those drugs can be in different strengths (ex., 0.5%, 1%, 2.5%, 5%, 10%).

In the 16 pages of discussion I finally got to the bottom line of when to dilate a healthy person with very low or no prescription who has no complaints or known medical conditions leading to eye disease. It would be done in their next recommended visit…..in 5-10 years! See the link below if you want to read the guideline. That lengthy period was an eye opener. Honestly, telling a patient to come back in 5 – 10 years basically sounds like we don’t want to see them again. But that’s what the guideline says. My own profession’s main association (American Optometric Association, AOA) says eye exams are recommended every 1-3 years for the same healthy individuals. That’s a conflict right there. There’s something even stranger about this. These vision plans that I accept, many times they allow an eye exam every year. There’s an incentive for everyone involved to possibly over-utilize health care here. And why not? Don’t companies want you to use things more often because they will make more money? That’s the American way.

Why dilate anyway? The main reason is an attempt to see the various “parts” of the back of the eye. We have to look through the pupils to do that, to see the retina, and the bigger the pupil opening the easier it is to see back there. It’s like peering into a mystery world that is unknown until we spelunkers go check.

Before anyone jumps to conclusions about what their eye doctor does or doesn’t do, you should be in good hands. This post isn’t about covering all the reasons for dilating either. Each doctor has their own routine for your routine eye exam. Just remember to tell them of anything you can recall about your eyes and vision. That will make it easier for your doctor to decide whether they may or may not dilate you. And just an interesting note about eye (iris) color….blue eyes generally dilate with less drugs than brown eyes and the length of dilation for blue eyes is also generally shorter but the same drop might work as well on both eye colors.


dilated vs undilated

dilated vs undilated


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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.




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