Wednesday, May 17, 2006
When I told you the story about the 3 sun-gazing sisters and solar retinopathy I alluded to the fact that bad chunks of vision don't appear as black spots... your brain tries to fill in the missing picture when you lose sight in one part of your visual field.
Which reminded me of a patient with macular degeneration... several actually, who were worried they were losing their minds because they were having hallucinations. Age-related Macular Degeneration (AMD) is a very common retinal disease which strikes many older people. When severe, it can wipe out the center of their vision. Now, the central vision is the part you really need in order to read or recognize objects. The retina outside that central portion is good for low light and movement detection, but not really reading or such.
There is something called "Charles Bonnet" syndrome in which people who have lost their vision start seeing formed images of things that aren't there. So say you are a patient with really, really severe AMD, so bad you have lost a huge chunk of the center vision in both your eyes. So here you are, with AMD, and you can't see anything in the middle... you can't just look "around" your blind spot because wherever you look, the blind spot goes. So your brain starts desperately trying to fill in that middle spot.
When the brain tries to fill in the side vision (as with the stroke patient I mentioned) it fills it in with smeary blurry stuff and that generally works out okay, because usually all you see off to the side normally is smeary blurry stuff. (Remember your side vision is usually pretty poor). But you’ve had a whole lifetime of seeing nice crisp images in the center. And after a while your brain starts getting really annoyed about the fact that it isn’t seeing some nice crisp images in the middle, and just starts throwing some random ones in there. Usually people see patterns.. like wallpaper, or brickwork, or trees... but sometimes it gets weird. One woman at Hopkins saw her dead husband (and she said she didn't even like him, lol!). A friend of mine had a patient that reported flaming skulls (gah!) and I had a patient in Chicago that was seeing purple gorillas.
So imagine you’re an old lady, and you can’t see too well, and you want to stay in your little apartment with your caretaker, and remain relatively independent...and you see purple gorillas. What do you do? Do you tell your kids about it the next time they visit and try to convince you to go into a nursing home?
Of course, these people think they are losing their minds and are terrified. I used to tell patients that this sometimes happened, and as long as they KNEW there really wasn't really a purple gorilla dancing in the bathroom, they weren't going loopy.
Hopefully I kept a few folks out of the mental rest home. Anyone with vision loss can get Bonnet syndrome, but I noticed it most with my AMD patients. In fact, I always asked my advanced AMD patients if they were seeing things... they often didn't volunteer the information because they didn't want to be hauled off to Arkham... and I was not surprised when many, many of them admitted to seeing things. Usually patterns, but sometimes more.