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Does Consensual Pupil Response Render An Eyepatch Useless?

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#1 Job99

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Posted 26 May 2023 - 05:13 PM

I was reading about consensual response but I couldn't find anything regarding it's importance or lack thereof pertaining to amateur astronomy. I also could not find any reference for the average strength of said response. I have read many times how people will patch up their observing eye and only take it off once they go to the eyepiece. It seems that many have tried this to keep their eye perfectly dark adapted in order to catch the faintest of targets like IC 434 for example, but now I'm wondering how much help this method actually is if the other eye is being stimulated by light. I've used a patch before, but not to keep my observing eye dark adapted, but rather to keep my non-observing eye relaxed without needing to squint or wink so hard. Interested to hear any of your thoughts! 


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#2 Redbetter

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Posted 26 May 2023 - 05:49 PM

The pupil response will only matter at the eyepiece for large exit pupil.   So if you are doing low power/large exit pupil observing of diffuse nebulae for example, then maximizing your own pupil has value.  For the rest of the observing medium or small exit pupils will be used and one's own pupil should not be an issue.

 

Pupil response to going from bright to dark is pretty rapid from what I recall reading.  I don't know how much wider it might be over several hours.  I remember something about it varying some after the initial widening, over only a few minutes, contracting somewhat, but this was not a large amount.



#3 TOMDEY

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Posted 26 May 2023 - 05:51 PM

No, the patch keeps the protected retina charged up and dark-adapted.    Tom


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#4 PeterAB

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Posted 26 May 2023 - 06:21 PM

Yes, the patch works.  Try an experiment on yourself.   Patch an eye for 15 to 30 minutes.  Expose the other to normal indoor lighting.   Step out into the dark and take the patch off.   Note the difference in naked eye limiting magnitude between eyes.  Note how much brighter the sky appears with the patched eye.

 

As noted above, dark adaptation is per eye at the cellular level.

 

I use a patch when I need light and I want to keep dark adaptation in one eye.

 

peter


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#5 Astrojensen

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Posted 26 May 2023 - 06:21 PM

No, the patch keeps the protected retina charged up and dark-adapted.    Tom

Indeed. And the effect is extremely pronounced and dramatic. I can personally attest to that. 

 

 

Clear skies!

Thomas, Denmark


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#6 Jon Isaacs

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Posted 26 May 2023 - 06:38 PM

I was reading about consensual response but I couldn't find anything regarding it's importance or lack thereof pertaining to amateur astronomy. I also could not find any reference for the average strength of said response. I have read many times how people will patch up their observing eye and only take it off once they go to the eyepiece. It seems that many have tried this to keep their eye perfectly dark adapted in order to catch the faintest of targets like IC 434 for example, but now I'm wondering how much help this method actually is if the other eye is being stimulated by light. I've used a patch before, but not to keep my observing eye dark adapted, but rather to keep my non-observing eye relaxed without needing to squint or wink so hard. Interested to hear any of your thoughts! 

 

The pupil dilates to fullest in a very short time, less that a minute.

 

Dark adaptation is actually a chemical process within the eye involving rhodopsin. It takes at least 30 minutes in the dark for the chemical aspect of night vision to develop. Light quickly bleaches the rhodopin so when you wear the patch, you are allowing you eye to dark adapt chemically.

 

Jon


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#7 Job99

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Posted 26 May 2023 - 07:33 PM

So if someone is observing in badly light polluted skies and the non patched eye is stimulated by all of that light, wouldn't it still limit how much maximum pupil dilation the observing eye can reach due to the consensual response? This would limit the maximum usable exit pupil of an eyepiece one could use correct?

#8 Job99

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Posted 26 May 2023 - 07:56 PM

Thank you for the responses by the way. It is making more sense now.

#9 NinePlanets

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Posted 26 May 2023 - 08:35 PM

From Wikipedia, the free encyclopedia:

A consensual response is any reflex observed on one side of the body when the other side has been stimulated.

For example, if an individual's right eye is shielded and light shines into the left eye, constriction of the right pupil will occur, as well as the left.

This is because the afferent signal sent through one optic nerve connects to the Edinger-Westphal nucleus, whose axons run to both the right and the left oculomotor nerves.

 

I suspect this phenomenon varies a bit from subject to subject. I know that keeping the eyepiece eye covered/closed when playing in the light helps a LOT with keeping my sensitivity to dim things active. But once again, it is the retina NOT the pupil that is corrupted by the light.



#10 dnayakan

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Posted 26 May 2023 - 09:02 PM

The pupil response is fairly quick but the buildup of rhodopsin takes time and is destroyed easily. 
 

The actual issue is the difference between generalized light (pollution) and glare. The consensual response is a problem when there is glare present - passing cars, porch lights etc. However, the pupillary response corrects fairly quickly when the source of glare passes. Wearing an eyepatch over the viewing eye when not at the eyepiece is to prevent rhodopsin bleaching, because that damage takes longer to undo. Light pollution (generalized glow which can be faint but not concentrated in a source) can be enough.

 

Eliminating the sources of glare reduces this problem a lot - selecting viewing sites, wearing deep hoodsed over shirts, bino bandit kinds of solutions help a lot. In the absence of glare, consensual pupil response is not too big of an issue.

 

I know some people who switch the eyepatch from their viewing eye to the other eye when they lower their head to the eyepiece as a way to combat this. They then switch the eyepatch back to the viewing eye when they step away from the eyepiece. This seems to have become an automatic response learnt over years. 

 

Cheers, DJ


Edited by dnayakan, 26 May 2023 - 09:03 PM.


#11 Job99

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Posted 26 May 2023 - 09:05 PM

Thank you for clarifying consensual response since I failed to do that thoroughly! I now understand that preserving the retina is the most critical part to detecting those faint objects and a patch is invaluable to that end. I was way off base on that part!


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