December 29, 2005

Ways of Seeing

The world looks different when your pupils are dilated.

Whenever we camp at a state park or any place that has big, well-lit public bathrooms, the kids and I do the night vision experiment. The experiment is pretty simple. You let your eyes get adjusted to the dark while sitting near a smoky campfire or talking a walk in the dark. Then when it’s time to go into the brightly lit bathroom before going to sleep at night, you keep your right eye closed and your left eye open.

For little kids, this means stumbling around with one hand over the eye while your parent tries to get you to brush your teeth or wash your face or use the toilet. Many of my friends have cursed me for teaching their kids to do this experiment. I think it's funny to watch all these kids in their pajamas, clutching toothbrushes and teddy bears, determinedly keeping one hand over their right eye. And it's worth the effort. Because then, when you leave the bright lights of the bathroom and walk back into the dark woods, you will have one eye with a fully dilated pupil and one eye with a pupil that is tiny. It's fun to stare into each other's eyes and see how bizarre this looks.

Of course, the real point of the experiment -- and you have to do this fast because your eyes will start adjusting again -- is to look at the dark world with first one eye, and then the other. Look out of your left eye, and the woods will seem dark, scary, impenetrable. Then close the left and look from the right eye, the one with the fully dilated pupil, and suddenly, the world is lighter. The dark masses look like distinct trees. The paths are clear.

Sometimes when I am having a hard time seeing something -- grasping, for instance, another person's perspective when it is completely different from mine – I remind myself about the night vision experiment, and how completely different the world can look when my pupil is dilated. I remind myself to be patient. I know from experience that sometimes I have to sit in the dark for 45 minutes before the full benefit of the night vision kicks in. And sometimes even then, I need to wait for moonlight.

Edited to add: If you are going to try this experiment with your kids, be sure to read the comments below.


Running2Ks said...

You surprise me all of the time, jo(e). I had no idea you were going there with this post. And then you did. You are a poet. I really love this perspective on acceptance.

And, it is a really cool experiment to try too.

Queen of West Procrastination said...

Oh my goodness, is that ever the coolest game ever. I think I can think of ways to do this at home (we live in a basement suite, and thus we live somewhere where it can get really really dark). Awesome. My husband's going to love this.

Ahem. Growing up, a little...

I wish I'd read this post before I'd gone out this evening, because I just had a good talk with some friends about real communication (and conflict resolution) requires gaining an understanding of the other's perspective. That illustration is perfect.

kabbage said...

Good reminder on seeing other people's perspectives.

Have you ever tried switching which eye dilates and which does not? I know my uncorrected vision is different between eyes, so I can get a slightly different perspective just switching eyes in normal light (although my uncorrected perspective is pretty darn blurry with either eye). Switching the hands with which you do everyday chores is a good way to bring mindfulness/awareness to what you do every day.

nancy said...


Lorna said...

wonderful wonderful post

Josephine said...

I learned this lesson today. Thank you for the post. I like the way you write.

Tjilpi said...

Sorry to be a party pooper but shining light into one eye causes the pupil in the other eye to contract making both pupils equal, even if one eye is covered. This is called the consensual response. This response does not occur when there is a relative afferent pupil defect - that is, if one eye has a damaged retina or optic nerve - shining light in it will not make the other pupil contract.

You can read about it here

jo(e) said...

tjilpi: But I've actually done this experiment -- many times -- and with kids who have healthy eyes. The pupils look different if you look into their eyes, and the visual effect I described happens as well. So there is definitely something going on.

In the experiment, we don't actually shine a light directly into the eye ... we are just walking around in a well lit room. So perhaps the intensity of the light makes some difference?

Tjilpi said...

Jo(e), I tried an experiment exposing each eye to a different light intensity.

I walked outside and looked directly at our midday summer sun with my right eye and kept my hand over my left eye. Then I came back inside into my darkened house, where the blinds are drawn to keep the heat out.

My pupils were the same size but there was a retinal after image in the right eye which made things quite blurry until it passed, while with the left eye I was able to see clearly.

I wonder if this is the source of the phenomenon you have observed.

One explanation for a difference in the size of the pupils might be that the kids have been enthusiastically pressing very firmly on their eyeballs. A blow to the eye can cause the pupil to dilate, and firm pressure might do the same thing for a while - I need to check that one out.

However, normally, light shone in one eye will make the opposite pupil constrict to the same degree.

Also, 20% of normal people have a slight difference in the size of their pupils. I wonder if you are seeing this?

jo(e) said...

This is going to lead to all kinds of experiments amongst my teenagers.

I just tried looking in the mirror and covering my left eye. Within seconds, I could see the right eye dilating even though it was uncovered. So that is the consensual response, right?

The fact that I could see it so quickly makes me see one of the flaws in our original experiment. When we are standing in the lit restroom looking at each other's eyes, we keep covering one up fast so that it doesn't get affected .... so we think we are comparing the two eyes and how they both look at the same time, but there is really a time lag between when we are looking at the right eye and when we are looking at the left eye.

Here’s the other part though: if I cover up one eye for a bit, and then look quickly into the mirror with both eyes, one pupil is larger than the other, although the effect does not last very long. BUT (and I just noticed this) it is the uncovered eye that has the big pupil and the covered eye that has the small pupil. (That totally refutes my original hypothesis, doesn’t it?) I think the reason I never noticed this before is that I am always looking into a mirror so it is easy to get right and left mixed up.

So here’s my new theory. When I cover up one eye, both pupils get larger due to the consensual response. But then for some reason, the firm pressure on the covered eye causes that pupil to contract. Firm pressure on an eye causing the pupil to contract would make sense as a protective adaptation, wouldn’t it?

I’m also wondering now if the visual effect – everything looking blurry and indistinct out of the covered eye – is also caused by the firm pressure on the eye. Right now, if I close my eye and put firm pressure on it, and then open it quickly, the vision from that eye is pretty blurry.

So all this time we thought we were measuring the effects of light vs dark, and instead we were seeing the effects of applying firm pressure to a closed eye ….

Of course, I have been trying this today with my own eyes, which are not the best choice for this experiment since I am 44 and I have had head trauma in the past. I will have to try this all again when the kids get home from school and we’ve got some young healthy eyes to experiment with.

Tjilpi said...

Sorry it's take time for me to get back on this.

The consensual response makes the pupil of the closed eye the same size as the open eye. It is the amount of light striking the open eye which causes both pupils to constrict or dilate to the same size. In a darkened room both pupils will dilate to the same size even though one eye is closed. In bright sunlight both will constrict to the same size even though one eye might be closed.

It is only in rare situations that pupil size will be different by more than half a millimetre (which occurs in up to 20% of the population.) For pupil size to be significantly different, and remain that way for more than half a second, there needs to be an underlying neurological defect, or previous trauma to the eye.

Normally, pressure to they eye, such as a squash ball hitting it, will result in dilation of the pupil of that eye, which will not constrict even if light is shone in the other eye. If there is not too much damage things get back to normal in a couple of days.