How to Assess Visual Fields with Confrontation Stimuli
[00:00] I want to demonstrate something to you about your visual field. Our visual field is cone shaped. It's not shaped like a box, so the farther away a stimulus gets from your eye, the wider your visual field is there. So if you can do this with me now, close one of your eyes and take your fingers and put it right at the edge of your visual field, nasally and temporally, but very close to your face, and notice how very narrow your visual field is there. Now move your hands out just about a couple of inches and you'll see your visual fields are a lot wider on that plane out there. Now move your hands all the way out. You'll see your field is very wide out here. The reason why I demonstrate that to you is it's important for you to understand that the farther away the stimulus is from the patient, the wider the visual field is going to be.
[00:52] The other reason it's important for you to understand that is because — if you're comparing your visual field with that of your patients — you have to show your stimulus halfway between you and your patient. Otherwise, you're not comparing the same parts of your visual fields. Let me demonstrate this to you. So I have my patient here, Abby, and I'm going to ask Abby to close... Go ahead and hold your hand up over your left eye and I want you to look right here at the side. Now I have my right eye closed and I'm having her look at my left eye so I'm having her look at the eye that's across from the one I am testing. The reason I'm closing my other eye is so I can compare my field with hers. Now I'm imagining dividing her visual field into quadrants and where she's fixating is right where the horizontal and the vertical quadrants meet. And I'm dividing her field into superonasal, infranasal, superotemporal, and infratemporal quadrants.
[01:56] I want to present my stimulus exactly, or as close as possible, halfway between me and my patient on this halfway plane. If I present the stimulus closer to me and I do it on the edge of my field, I'm going to be way inside her field because her field's a lot wider out here than mine is. Mine is a lot more narrow. Conversely, if I show the stimulus closer to her than to me and I showed on the edge of my field, I'm going to be at the edge of my field. But I'm going to be way outside her field because her field's a lot more narrow on this plane than mine is. So make sure that you're showing the stimulus halfway between you and your patient. So go ahead and look right here at my eye and tell me how many fingers I'm holding up.
[02:57] Very good. You can uncover your eye. I want to just explain a couple of things here. First of all, I made sure I was halfway between myself and my patient when I showed the stimulus. When I went up to show the stimulus, I'm asking myself, am I on the halfway plane? When I'm satisfied with that, then I say, am I on the edge of my visual field? Only then do I show the stimulus. You don't want to have your stimulus showing as you're finding the edge of your field, or the halfway plane, because then the stimulus becomes a kinetic stimulus and kinetic stimuli are easier to see than static stimuli. So your first strategy should be using a static stimulus, not a kinetic or moving stimulus because they're easier to see than aesthetic stimulus. The other thing that I want to point out to you is that when I showed her more than one finger, I aimed my fingers so she could tell it was two fingers because if I'm — go ahead and cover this eye again.
[03:56] If I am showing her two fingers at this angle, she can't tell that's two fingers. It doesn't look like two fingers to her. I need to aim my fingers so that she can tell that there's two there, so now I'm going to check her other eye and watch for those little subtleties that I just pointed out. So go ahead and cover your other eye, Abby, and now I'm going to close this I of mine, so I can compare my field with hers. I'm going to have her fixate on the eye across from the eye I'm testing. So look right here at my eye and tell me how many fingers I'm holding up.