optic nerve lesion

[trgf]

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I was trying to use the image in Netter (http://www.netterimages.com/image/retinogeniculostriate-visual-pathway.htm) in order to predict what lesion-associated visual field problems one would get, and I got totally confused. For instance, a lesion of the outer optic nerve should correlate with visual defect in the nasal hemifield, but the diagram doesn't show you that if you trace the lines; instead you'll get a defect in the temporal field. Could someone please explain? Thanks!

 

[aliDO]

I would just study the half page in FA and not get too overwhelmed with it. 10 minutes of studying tops and you should be able to get any question correct that you get.

 

[Ty Webb]

I think you're disregarding the fact that the image as received on the retina will be in reversed orientation as that of the actual object. For instance, objects in the center of one's vision will create an image on the lateral ("temporal") retina, whereas objects located more peripherally will create an image on the medial ("nasal") retina. You'll also have an analogous top-bottom reversal that will explain why lesions of Meyer's loop, etc. affect the hemisphere that they do.

For example, in bilateral temporal hemianopsia, you lose ability to see at the periphery of your visual field. This is due to disruption of the crossing fibers of the medial retina.

Hope this helps.