Why photophobia is a problem for us


Posted by Lynn Yarbrough , Dec 08,2001,18:56   Archive
I have been thinking about photophobia and believe I may have an explanation of why BEB'ers have that problem, and why it bothers them so much.

The iris of the eye is a "light valve" that regulates how much ambient light gets to the retina in the back of the eye. It opens and closes -- camera lenses also work this way -- to protect the retina from overexposure. It appears to take about a second to make the transition from open in darkness or shade, to closed in bright sunlight.

Normal blink duration for people is about 1/20 second. During normal blinking, the iris does not have time to adjust to the reduction in light, so it stays somewhat closed during the duration of a blink. After the blink, you don't notice any change in intensity.

Blink duration in a spasm is several seconds, at least 20 times that in a normal blink, so the iris opens during the spasm. Then when the eyelid opens, the iris has to close again against the light. During that short interval the retina gets bathed in bright light, which is bad for you, and your system reacts to it.

Not that this helps your photophobia, but perhaps knowing this can help those of us who are really bothered by it to make some adjustmemts in how we deal with bright light.

--- Lynn




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Re: Why photophobia is a problem for us

Re : Why photophobia is a problem for us --- Lynn Yarbrough
Posted by Sally - in - Idaho , Dec 08,2001,21:42 Top of Thread Archive
That took some deep thinking on your part, Lynn! Sounds like you've come up with the reason for ... now if you could only find a solution to the photosensitivity. Keep thinking!! Thanks for sharing this.

Sally in North Idaho who is extremely photosensitive ... that is worse for me than the spasms.




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Re: Why photophobia is a problem for us

Re : Why photophobia is a problem for us --- Lynn Yarbrough
Posted by Dee in OR , Dec 09,2001,00:48 Top of Thread Archive
Thanks Lynn. Have you submitted this to the BEBRF? You should!

Dee in dreary Oregon




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Re: Why photophobia is a problem for us

Re : Why photophobia is a problem for us --- Lynn Yarbrough
Posted by mary ledbetter (MARY LEDBETTER,mary ledbetter), Dec 09,2001,20:31 Top of Thread Archive
Lynn, I have one eye that has a larger iris according to my Dr.It is the left and has closing than the other. Thank for your information.



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Re: Why photophobia is a problem for us

Re : Why photophobia is a problem for us --- Lynn Yarbrough
Posted by kathy , Dec 10,2001,07:33 Top of Thread Archive
THAT is really interesting , lynn. usually when i have severe spasms i have to put on my dark glasse to help calm my eyes down; these are the spasms triggered by exposure to really bright light. it sometimes takes hours for these to go away. also maybe it explains the ones triggered by websites where you have to change the focus of what you are looking at, like maybe the pupil has to expand and contract too rapidly.

--modified by kathy at Mon, Dec 10, 2001, 07:37:02




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