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Independent pupil size. (1 Viewer)

B

Binastro

Well-known member
Just watching 'The Shrink is in' 2001.

The lead actress, 13 minutes into the movie displays one pupil of 3mm and the other 4.5mm.

Do the pupils of our eyes normally operate independently, depending on light levels entering each eye, or are they synchronised to operate together?
 
Binastro said:
Just watching 'The Shrink is in' 2001.

The lead actress, 13 minutes into the movie displays one pupil of 3mm and the other 4.5mm.

Do the pupils of our eyes normally operate independently, depending on light levels entering each eye, or are they synchronised to operate together?
Click to expand...

I believe they normally operate in synchrony, but a fair percentage of the population has [Anisocoria] as described in the wiki article.

I'm not sure what happens if each eye is deliberately presented with different amounts of light, but that could easily be determined experimentally. An interesting question would be whether the two retinas adapt separately to different light levels.

Ed
 
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Thanks Ed.

As usual, things are more complicated than one would first think.

She looks fine, recently sitting on the beach, so nothing serious I suppose.
 
elkcub said:
An interesting question would be whether the two retinas adapt separately to different light levels.
Click to expand...

Hi,

since dark adaption of the eye is biochemistry (Rhodopsin being bleached by light and then dissociating - it needs time to reform Rhodopsin), I would guess that it's independent.

At least it looks like that to me from astronomy where observing a bright object like luna or bright planets will leave you with one dark adapted eye seeing well in the darkness and one not so much...

Joachim
 
Example of pupils that appear to operate independently
 

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There is an easy test for relative pupil sizes. In daylight focus a binocular at infinity and observe an artificial star (glitter point of the sun in a small shiny object, etc.) from about 3-4m away. The diffraction patterns formed by the highly defocused star are projections of the pupils of the eye. You can easily compare the sizes, but beware that both magnification and diopter setting affect the size of the diffraction discs. Repeat with the binoculars inverted to be sure the any observed difference is the eye pupils. The same test can be done with real stars at night by setting the binoculars at close focus instead of infinity, but be sure (night or day) that the exit pupil of the binocular is larger than the entrance pupil of the eye.

I always see a small difference in my eyes in this test. The left dominant eye pupil is always a fraction of a millimeter larger than the right pupil.
 
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jring said:
Hi,

since dark adaption of the eye is biochemistry (Rhodopsin being bleached by light and then dissociating - it needs time to reform Rhodopsin), I would guess that it's independent.

At least it looks like that to me from astronomy where observing a bright object like luna or bright planets will leave you with one dark adapted eye seeing well in the darkness and one not so much...

Joachim
Click to expand...

Oh yes. Looking at the moon, or Jupiter through a scope definitely creates a huge difference between the eyes. I used to save those views for either the end, or the beginning of an observing session (at dusk) so as to preserve adaptation for the rest of the time.
Also, if one has to get up from bed in the night, and a light is needed to navigate, try keeping one eye shut, until all the lights are out again. Then compare the vision between them. Whether it is chemically triggered, pupil size, or both, the noise level in the recently illuminated eye, faced with a dark fov is quite interesting.

Bill
 
jring said:
Hi,

since dark adaption of the eye is biochemistry (Rhodopsin being bleached by light and then dissociating - it needs time to reform Rhodopsin), I would guess that it's independent.

At least it looks like that to me from astronomy where observing a bright object like luna or bright planets will leave you with one dark adapted eye seeing well in the darkness and one not so much...

Joachim
Click to expand...

Yes, I agree with you and wdc. :t:

Ed
 
I just tried something new with the glitter point set-up I described above. I shielded my right eye completely from any side light leaking in around the eyecup and placed an LED flashlight bulb close to the side of my left eye with that eyecup collapsed to expose my left peripheral vision to the LED. Both pupils shrank, even though only the left eye was exposed to the extra light, but the left pupil shrank more than the right one.
 
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