Re: Dark adaptation on exit pupil size

From: eric bazan (boo_at_fractalfreak.com)
Date: 09/07/04 

Date: 7 Sep 2004 15:44:54 -0700

billferris@aol.comic (Bill Ferris) wrote in message news:<20040907104734.07582.00000295@mb-m11.aol.com>...
> canopus wrote:
> >One would expect to find a reduction in the ability to see faint stars
> >with the naked eye with age, since a reduction from 6.9mm (15 year
> >olds) to a 6.2mm (50 year olds) in average dark adapted eye pupil size
> >corresponds to about a 20% reduction in the eye's light grasp.
>
> However, 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. I'm
> not aware of research showing a correlation between pupil size and naked eye
> limiting magnitude among experienced observers. All the research I've seen
> points to the chemical process as the key to dark environment light
> sensitivity. So, while there may be age-related degradations of scotopic
> vision, I wouldn't assume constriction of the eye pupil to have a measurable
> impact.
>
> Regards,
>
> Bill Ferris

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.

Animals that rely on their eyes at night tend to have large pupils -
even if they are very small. Your everage 10 pound houscat probably
can dilate its pupils to over 8mm - more than most people. Some
of the screech owls I've come across while hiking at night have
enormous pupils - larger than a persons, and these are not large
birds. An owl has an impressive retina when it comes to dark adaption -
and a large pupil to match. Birds with smaller pupils tend not
to be noturnal, again leeding some credence to the importance of
pupil size.

-Eric

Relevant Pages

  • Dark adaption and pupil size - an experiment (longish)
    ... when I was about six years old looking though a neighbors reflector ... The 11x80 bincos were very impressive from a dark ... I'd do an interesting experiment to see if increasing my pupil size ... often used in eye drop form by eye doctors to dilate patients ...
    (sci.astro.amateur)
  • Re: Why is the sky red?
    ... Sorry but the red eye effect has nothing to do with the colour of the iris. ... Normally the pupil looks black because almost all of the light that enters ... you see a red colour from the blood in the retina. ... The same principle happens with flash photos. ...
    (sci.astro)
  • Re: Accommodation in Aphakial Eyes -- Bates has not been disproven on this.
    ... noticeable to the naked eye. ... about the normal eye is how much the pupil is constantly adjusting for ... I think it is true that the amount of sun energy entering a healthy ... And importantly the retina has the ability to adjust its light ...
    (sci.med.vision)
  • Re: Battery/lighting philosophy for fully-loaded touring?
    ... Really bright lights result in a lot of light ... It takes about 45 minutes for the retina to become fully dark ... There is a theory that you can shut one eye when that happens to keep ...
    (rec.bicycles.tech)
  • Re: Dark adaptation vs. pupil size
    ... >dark adaptation is primarily a chemical process within the eye. ... >> 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. ...
    (sci.astro.amateur)