Sunday, October 02, 2005

The Purkinje Tree



This drawing was scanned from Histology by Arthur Worth Ham, J. B. Lippicott Co. 1957, page 854. It shows the "fundus" of the right eye as seen through the ophthalmoscope. Those branching lines are the blood vessels of the retina.

When the ophthalmologist examines your eyes, as that exceedingly bright light shines in, sometimes you will glimpse for a moment a complex branching network which looks very much like the inside of a tree (without leaves). One of the names for this image is the "Purkinje tree" named for the Bohemian physiologist Jan Evangelista PurkynÄ› (or Purkinje) (1787-1869).

I asked about this once, and the ophthalmologist told me we always see that tree, but our brain automatially filters out the image, so we are normally never conscious of it. Only when the lighting within the eye is "different" will it become visible (as during certain eye examinations).

As a Chestertonian, I found this very unsettling, thinking of Eden's Forbidden Tree of the Knowledge of Good and Evil... somehow the image is still with us, but our brains - or perhaps our eyes - have changed...


Most probably we are in Eden still. It is only our eyes that have changed.
-- G. K. Chesterton The Defendant, page 3


Alas.... only once in a great while, then, when we have a light of exceeding brightness, can we see things are they really are...

7 Comments:

At 02 October, 2005 18:17, Blogger rhapsody said...

"The eyes of both of them were opened."

SOMETHING changed...

 
At 07 October, 2005 20:44, Anonymous Anonymous said...

Hi Dr. T,
Off topic- was banned early today from your blog- as I'm on now I'm assuming it was a system glitch, but wanted to let you know.
Would have emailed instead, but am not sure that you have the same email address-
And I hope you would email me if there was an actual problem...


Faith

 
At 09 October, 2005 18:55, Blogger Dr. Thursday said...

I don't understand. I have neither banned nor un-banned you, nor anyone else!

Indeed, I have have not touched this mechanism for some time (being rather busy at present, yes, even on the weekend!)

I must conclude this is a "blogger" problem.

 
At 09 October, 2005 22:08, Blogger rhapsody said...

Was banned & unbanned at another blog, also.
It must have been a temporary problem.

's ok, Dr. T...
:)

 
At 11 October, 2005 08:59, Blogger Nancy C. Brown said...

Fascinating, the info on the "tree" in our eye. Makes me think of removing the plank in my eye before trying to get the speck out of another's...
And now that you mention it, I do remember learning this in nursing school...just haven't used the info in a long time.
You make some fasinating connections, Dr. T with biology and life and Chestertonianisms and God. Good stuff.

 
At 10 September, 2008 00:31, Anonymous Emma said...

So fascinating, in fact, that I'm studying these Purkinje Trees in my Psychology Report at Sydney University and the relationship between how quickly these trees disappear (because it takes varying times in different people we discovered!) and whether people have a good ability to 'fill-in' their blind spot - will let you know the results!

 
At 13 April, 2009 15:17, Blogger TraceyS said...

I seem to see this when I press my eyelids down wiht the palm of my hand (gently). It seems to stimulate the tree to appear so when i open my eyes and look at something white and then blink like a few times, I see the tree, although it only stays visible for a millisecond and only reappears with each blink. After a few blinks, the image fades away.

I also just noticed that when I give my eyes a rest such as closing them for a couple of minutes, and then suddenly jerking them open, I notice that I see the tree again. I dont think this was due to pressure being put on my eye such as the palm of my hand or squinting the eye.

Im not sure but has anyone experienced something like this where they get the tree after putting pressing on their eye?? cos im thinking that it might be to do with the internal eye pressure...


Also it happens in my right eye only.

 

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