Hello there everyone,
On the topic of light sensitivity in chiari pts, I just wanted to say that
ever since I was a child I could not handle light. Bright sun would give
me a headache, even regular room light would do it. I was never without my
sunglasses, winter or summer ( still will not leave the house without
them). As an adult I have manipulated my environment enough to minimise the
light...my blinds are always at least partially drawn, when I worked I
often worked the night shift etc.
To shine a light in my eyes for exams or whatever was torture and would
make tears spill out.
Why would this happen to so many of us?
Well one explanation is that the 3rd cranial nerve (Ocularmotor) innervates
the sphincter of the iris and the ciliary muscles which are invlved with
adaptive pupillary dilation/constriction response. It also innervates the
extrinsic eye muscles.
This nerve exits the brainstem in an area particularly sensitive to
compression from chiari. Thus any compression or damage would affect the
response of pupils to light (delayed or they may not constrict enough to
filter out the proper amount of light) as well as the adaptation of near
vision to far...(like when you are looking at a book and reading then look
up across the room at the TV and have to wait until your eyes focus
properly...this is a delay in accomodation and I have found it is common in
many chiari pts).
This also makes the chiari pt more aware of the flickering of things like a
computer screen, fluorescent lighting and the like. These subtle pulses of
light, unnoticed by others, create an overall stress in our eyes becasue of
the extra muscular strain and delay involved with adapting to the
changes...we notice it more becasue it takes our eyes seconds rather than
milliseconds to adapt to the flicker.
I *discovered* the computer screen thingy on my own when doing my original
research and asking very specific questions of my respondants...everyone
was like...hey you mean somebody else notices this? I have mentioned it to
both Dr. Menezes and Dr. Milhorat and am tracking just how many people have
these weird visual affects.
So many people would tell me my eyes are not working properly but my eye
doctor can't find anything wrong...this delay in accomodation accounts for
a lot of it. One of the tests for it is to put a sign or some poster on
the wall....sit about 10 feet away with the lights on. HAve someone else
with you, with a flash light. HAve them shine the flashlight on the
lettering...then turn the light off...how long before you see the same
stuff you could see with the lights on clearly?
In an average person this adjustment is milliseconds and there is no delay
ina being able to adjust...but in chiari pts you will often find that the
accomodation delay means it takes a few seconds before they can see the
lettering clearly...sometimes longer.
As for opening the eyes really wide this increases intra-optic pressure
which could very well be painful for a chiari pt. I can not open my eyes
really wide and the worse the pressure is in my head the more closed my
eyelids are.
My pupils are usually dilated over 6mm and while they react to light if you
look closely you will see the iris does not stay constricted with light it
keeps trying to open. They also do not constrict to the small size they
should with bright light. Since my last surgery my vision is much better so
I am willing to accept the other weirdness. : )
Hope this helps, I can see all of us at a chiari seminar some day...we'll
be the group all in dark glasses...it will look like some Ray Ban
convention or something! : )
Take care
Darlene
