birth defect

Andrew Ray aray at
Mon Aug 14 19:24:13 EST 1995

In article <1995Aug14.161228.37319 at>, spkaslm at (Stephen 
Maidment) writes:

>In article <40g1af$mb7 at>, shiela at (Anderson 
) says:
>>I hope someone out there can help me out, or at least point me in the
>>right direction.  
>>A friend of mine has a daughter, 8 years old now that was born without
>>an eye.  I heard somewhere that there is a surgical procedure that will
>>allow sight (as long as there is an in-tact optic nerve).  Does anyone
>>know of this procedure? 
>>shiela at
>Forgive me if you have already received my reply but according to this 
wretched machine the
>message did not transmit properly. 
>What I said in my reply was that it is unlikely that any such procedure 
exists. The problem 
>is that the visual pathways have to have been active from birth in order to 
establish the 
>correct connections and disconnect unwanted ones. This process is usually 
complete by around 
>the age of 5 years, after which no further development can take place. Any 
such procedure, to 
>be successful would have to be performed on an infant and would be unlikely to 
succeed in an 
>eight year old.
>Even if she can see with her existing eye, this will transmit visual 
information predominantly
>to one side of the brain only. The other side of the brain, even if served by 
an intact optic 
>nerve will have never received any input from this nerve and will therefore 
have been unable to
>develop into functional visual cortex.
>The short answer is that it is unlikely that any amount of surgical 
intervention will enable her
>to see at this late stage in her development. I would stress that this reply 
is purely conjecture,
>I am not a neurosurgeon so I would be interested to hear from anyone who has a 
different opinion.
>Steve maidment. 

While I agree with most everything you said, there is good evidence to suggest
that during visual development, the input from the functioning eye will spread
throughout the visual cortex - some input goes to the same side, some to the
other side.  The input would normally be confined to columns and groups of 
columns of cells.  However, if I remember correctly, the columns getting input
from the dysfunctional eye will develop to have input from the one good eye.
Unfortunately, I think you're probably right about the surgery not being able
to fix things.

Andrew Ray
Dept of Neuroscience
Emory Universit

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