Visual field defects. Totally confused. Please help

[sameeralord]

Visual field defects. Totally confused. Please help!

Hello everyone,

[PLAIN]http://img827.imageshack.us/img827/2756/picsds.gif

I'm totally confused with this. If there is a lesion in A, why can't you see the left visual field. According to the arrows, if there is a lesion at A, you would not be able to see white areas in pic C. Are they talking about a particular eye or what you see, please either way I don't understand this. What I'm thinking is if there is a lesion at A, when you look at an object you see an object with some areas missing, I'm assuming this is wrong and you can see a whole image in lesion A, but I don't understand. Your help would greatly appreciated. Thanks

 

[sameeralord]

What I mean is, this is paris seen from normal eyes

I don't understand this pic. Why do we see 2 things, don't we see only one thing with our eyes. For me this is like double vision.

Paris with bitemporal hemianopia

 

[Borek]

It is not double vision. Keep your head immobilized, look directly ahead. Close left eye, check what you see with your right eye peripheral vision (check how far you can see). Now close right eye, open left. Can you see things on your far left? Don't move your eyes, although even if you move them, you will see pictures are different.

 

[sameeralord]

It is not double vision. Keep your head immobilized, look directly ahead. Close left eye, check what you see with your right eye peripheral vision (check how far you can see). Now close right eye, open left. Can you see things on your far left? Don't move your eyes, although even if you move them, you will see pictures are different.

Thanks Borek but I'm still thinking I'm missing a trick here. Ok so does the normal paris picture show what you see in each particular eye, but in reality does the brain merge these 2 images together and give us one image?

 

[Borek]

Brain combines the pictures, even if they are not identical. They are not identical in two ways - first, they are seen from slightly different points, and parallax information is used to estimate the distance. Second, each eye sees parts of the picture that the other eye is simply not able to see - even if they are both facing ahead, their field of vision do not overlap completely. Peripheral vision is not that precise, and the distance information is not needed - however, from what I remember, our peripheral vision is very sensitive to movements. That makes sense - you don't have to see exactly what is happening, but if something moves it better catches your attention.

 

[sameeralord]

Brain combines the pictures, even if they are not identical. They are not identical in two ways - first, they are seen from slightly different points, and parallax information is used to estimate the distance. Second, each eye sees parts of the picture that the other eye is simply not able to see - even if they are both facing ahead, their field of vision do not overlap completely. Peripheral vision is not that precise, and the distance information is not needed - however, from what I remember, our peripheral vision is very sensitive to movements. That makes sense - you don't have to see exactly what is happening, but if something moves it better catches your attention.

Thanks again Borek Now this is the question that has been bothering me. Now I can finally put it into words. So person with bitemporal hemianopia, what does he see. Does he see the 2 images merged. What kind of image that would be? Could the image have a dark band in the middle. Like image-darkband-image?

 

[Borek]

No idea So far it was just basic optics and things you can test by yourself and on yourself, when it comes to strictly biological/medical/neurological aspects I know about as much as about GR.

 

[Lievo]

I'm totally confused with this.

Yep, that's a frequent loophole in this kind of figure: a refers to the eyes while b and c refer to the visual field.

What I'm thinking is if there is a lesion at A, when you look at an object you see an object with some areas missing, I'm assuming this is wrong and you can see a whole image in lesion A

You're correct it's wrong: you'll see most of the visual field (but for a small part at the far temporal side but this figure doesn't go into such distinction).

So person with bitemporal hemianopia, what does he see.

You can use a sheet of paper to prolongate your nose. That will make you have a bitemporal hemianopsia (except for a small spot in the middle of your field of view: the longer the sheet of paper, the smaller it will be).

 

[Lievo]

Paris with bitemporal hemianopia

This figure from wikipedia doesn't work. Each visual scene shoud be inverted to reflect what the each retina sees. So the illustrations of the defects are inverted in the correponding wikipedia pages: nasal hemianopsia is illustrated with the temporal one and the temporal hemianopsia with the nasal one.

Homonymous hemianopsia is well illustrated, although the visual scene of each eye miss. I guess the contributor tried to put it and realized it was not working for a reason s/he didn't understand. If someone can contact the contributor and explain the problem... I'm not used to contribute myself...

 

[mtc1973]

What I can say is that I have been on prescription drugs in the past and was looking at a cashier in the supermarket. I knew something was wrong but couldn't quite figure it out. Then I realized she had no face. The drugs seemed to be giving me blind spots but I really had to concentrate to be aware of them - our brains have a brilliant capacity to literally fill in the blanks! I took me some time to realize there were portions of my field affected.