Question - Optic tract lesion?

[trp2006]

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If you have lesion in the optic tract, does the pupillary light reflex gets affected or remains normal? I'm confused because in two different sources, there were contradicting information. Thanks for the help!

 

[SomeDoc]

If you have lesion in the optic tract, does the pupillary light reflex gets affected or remains normal? I'm confused because in two different sources, there were contradicting information. Thanks for the help!

Lesion in an optic tract will still lead to pupillary light reflexes. This is because the contralateral optic tract still compensates for pupilary light reflexes in both eyes.

 

[vgirl712]

Direct pupillary reflex in the affected eye is gone. Shining light into the affected eye will do nothing.

Consensual pupillary reflex in the affected eye works--as in, shining the light in the other eye will still make the affected eye's pupil constrict.

Edit: ah, misread the original post. Disregard! Sorry about that.

 

[SomeDoc]

Direct pupillary reflex in the affected eye is gone. Shining light into the affected eye will do nothing.

This is an indication of damage to the optic nerve, and not the optic tract.

 

[trp2006]

Thanks guys. If the pupillary light reflexes are intact in the optic tract lesions, then how do you differentiate between lesions of optic tract vs. visual radiation?

 

[UditNarayan]

to differentiate lesions of the optic nerve, optic tract, and radiations, you can focus on the patients visual fields. for optic nerve lesions (if complete), the patient has lost vision of one entire eye. for optic tract lesions, its more like contralateral homonymous hemianopsia. for radiations, it depends on which loop you are talking about, but in general would lead to a contralateral quadrantanopia. step 1 is a bit removed for me, so im not sure if im remembering this stuff accurately. it can get a little more confusing with partial lesions/ablations, where only one portion of the nerve or tract is severed...

 

[trp2006]

to differentiate lesions of the optic nerve, optic tract, and radiations, you can focus on the patients visual fields. for optic nerve lesions (if complete), the patient has lost vision of one entire eye. for optic tract lesions, its more like contralateral homonymous hemianopsia. for radiations, it depends on which loop you are talking about, but in general would lead to a contralateral quadrantanopia. step 1 is a bit removed for me, so im not sure if im remembering this stuff accurately. it can get a little more confusing with partial lesions/ablations, where only one portion of the nerve or tract is severed...

If we assume complete lesion of the optical visual radiations (not individual Meyer's loop etc), then you get contralateral homonymous hemianopsia, which is the same as a lesion with optic tract lesion. Initially, I thought that you could differentiate those two based on pupillary light reflexes (since some of the optic tract fibers also project to the pretectal area, superior colliculus etc), but if the pupillary light reflexes are intact in the optic tract as well, then I don't know how to differentiate between the two lesions?

 

[SomeDoc]

If we assume complete lesion of the optical visual radiations (not individual Meyer's loop etc), then you get contralateral homonymous hemianopsia, which is the same as a lesion with optic tract lesion. Initially, I thought that you could differentiate those two based on pupillary light reflexes (since some of the optic tract fibers also project to the pretectal area, superior colliculus etc), but if the pupillary light reflexes are intact in the optic tract as well, then I don't know how to differentiate between the two lesions?

Clinically, you won't be able to differentiate the difference between a right optic tract lesion and a complete lesion of the right optic radiations, as both contain the same nerve pathways, and will thus produce the same result (contralateral homonymous hemianopsia).

 

[SomeDoc]

Thanks guys. If the pupillary light reflexes are intact in the optic tract lesions, then how do you differentiate between lesions of optic tract vs. visual radiation?

This can be done only if there is a partial lesion to the visual radiation (ex. meyers loop only). The differentiating factor will be left upper quadrantic anopsia in both eyes (right meyers loop lesion), versus left homonymous hemianopsia (right optic tract lesion).