Re: Dark adaptation vs. pupil size

From: SaberScorpX (saberscorpx_at_aol.com)
Date: 09/08/04 

Date: 08 Sep 2004 16:34:00 GMT

>dark adaptation is primarily a chemical process within the eye. The
>> additional light grasp of the fully dilated eye pupil accounts for just a
>> fraction of the total improved light sensitivity of the dark adapted eye.

>while there may be age-related degradations of scotopic
>> vision, I wouldn't assume constriction of the eye pupil to have a
>measurable
>> impact.

>While it's true that most of the sensivity of the dark adapted
>eye is in the retina, pupil size is important too. Going from a 7mm
>to a 6mm pupil will decrease the amount of light the retina
>receives by over 30%. Assuming that the sensivity of the retina does
>not change (eye already full dark adapted) this could be significant.
>Especially if you are observing 'naked eye' or just going for a walk
>in the dark.

Increased pupil size certainly increases light gathering capability.
The accompanying gain in peripheral/averted vision potential in low-light
conditions by triggering the rods into a greater capacity should be considered
an important part of dark adaptation and observing. (This alone would also help
explain a nocturnal animals' advantage in evolving relatively larger pupils.)
But increased sensitivity to that light-gathering capability is, as stated,
a vital but separate, chemical process. And without the contribution of this
process, the benefits of light-gathering capability would be severely limited.
Additional light grasp and improved light sensitivity are two different issues,
but I believe both processes are important for dark-adaptation and observing.
A couple of good articles:
http://www.asnsw.com/universe/1997/darkadap.htm
http://www.nutraceuticalsworld.com/May022.htm
Also, on the subject of visual purple, it has been found that, along with the
benefits of vitamins A and C, blueberries/bilberries are effective not only for
increasing the speed of rhodopsin generation, but for improving
microcirculation as well as overall eye health and reducing eye strain.

SSX

 
 

 

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