Re: Nerve cells in blind mice retain their visual function

On 11/29/2024 3:04 AM, Liz Tuddenham wrote:

I recently heard that the presence of a third type of photoreceptor cell
has been detected in the human eye.  As well as rods and cones, there is
a more primitive light-sensitive mechanism for setting the body clock.

I was recently in the room with a relative who was being tested with an unusual method.  They were asked to look at a target, close their eyes, and then touch the target.  They missed by several inches.  Then the Dr. would put a colored filter in front of their eyes *after* the eyes were closed -- and certain colors would improve their ability to find the target.  I would not have believed it if I had not watched it personally.
There's a video of the technique here:
https://www.youtube.com/watch?v=qA_tjGCFzgg
using a ringing bell instead of a visual target.  The video doesn't point out that the test is done with eyes closed, but it is.
It takes several weeks to adjust to wearing the special glasses that are prescribed; at first my relative could only wear them for two or three minutes lying down in a dark room with eyes closed, before feeling dizzy.  After a month or so they had built up to the point of being able to wear them all day.  And the glasses* were a big help in treating their symptoms.
I asked the Dr. how colored lenses could have any effect on closed eyes, and they said that there are pathways from eye to brain that are very sensitive to light but do not connect to the visual cortex.  It's pretty amazing to see it in action.
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*BTW the colored filters are used only for diagnostic purposes.  The glasses themselves are not colored.
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I'm part of the vast libertarian conspiracy to take over the world and leave everyone alone.