ssrpk
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A 59 year old retired autoworker complains of walking into things on his right. He trips over chair legs with his right foot and has trouble driving because he has difficulty seeing cars entering an intersection from the right. A neurological exams reveals a corrected vision of 20/20, normal ocular mobility, and no sensory or cranial nerve deficits. Both pupil reacts briskly to light, and the near response is normal. Visual feilds testing reveals right homonymous hemianopsia.Where might the site of the lesion be located?
a- Optic tract on the left.
b- Meyer's loop on the left
c- Primary visual cortex on the left occipital lobe
d- Visual radiations on the left.
e- Frontal eye field on the left.
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| kkr
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is it D
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| KEROCHI
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A. left optic tract lesion
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| mesh
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its A....
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| ssrpk
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normal pupillary light refelxes rule out any lesions involiving nerve or tracts!
lesions involving primary visual cotex is ususally a/s with macular sparing!
correct answer is D
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| pgn
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jus for more info
why is macula spared in visual cortex lesions?
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| ssrpk
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duaL blood supply!
branches of PCA a/a MCA
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| hgy
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Seems like lesions to unilateral optic tract will not hurt pupil reflex. Could you explain more in detail?
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| Galaxum
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Hi hgy and all,
Seems like lesions to unilateral optic tract will not hurt pupil reflex. Could you explain more in detail?
_ Loop of neurons is responsible for the pupillary light reflex: Optic tract -----> pretectal area ---> parasypathetic neuron E-W nucleus (Part of oclumotor nucleus)---> send axons within the oculomotor nerve and terminate in the ciliary ganglia ---> projects axon to the sphincter muscles of the iris.
_ But visual axons in each optic tract project to the E-W nucleus bilaterally. So when light is shown in one eye, there is constriction of the pupil not only in the ipsilateral eye (the direct light reflex) but also in the contralateral eye (the consensual light reflex).
Hope you agree with that.
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| Galaxum
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Hi Ssrpk,
if you think the consensual light reflex is right, then" normal pupillary light refelxes rule out any lesions involiving nerve or tracts! " is not sure. Only one place affecting pupillary reflex in optic pathway is chiasm (except primary visual cortex). In this case, clinical presentation will be different.
If the answer D is only one, it needs more explaination.
thanks for your post
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| hgy
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Galaxum, Thanks. I agree with you. I also want to point out that lesions to visual radiation usually cause quadrantanopia not hemianopia.
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| hgy
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Galaxum, Actually I think optic nerve lesion of one eye will lead to loss of the direct pupil reflex of the lesion eye and indirect pupil reflex of the fellow eye. While lesion to optic chiasm should not affect pupil reflex.
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| Galaxum
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Hgy, pupillary reflex dont use the optic nerve, but via the oculomotor. in this ptwy, only one intact optic nerve, tract, radiation... is enough to trigger the light reflex.
_ So, when chiasm is affected, it means that both optic nerve cant conduct the signal, then light reflex will be lost.
_ one of the clinical uses of pupillary reflex is used to evaluation the brain stem lesion in cranial trauma coma. Oculormotor nucleus is compressed there.
I agree with you, if quadrantanopia would be the symptom, the correct answer were D
if not, A or D are the answer.
_ So from this point, we can deduce when the patient losts light reflex in one side.
I hope you all agree with me.
thank
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| hgy
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Galaxum, Optic nerve is the afferent for light.
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| Galaxum
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Yeah, Hgy! afferent for light signal reach cortex
Iris plays a role in adjust pupillary size, via efferent occulormotor, ciliary, parasynpath
If primary visual cortex is intact will control this action, and cortex, occulomotor, iris is efferent ptwy of this reflex,and optic tract sends axon to pretectal area to the other side. is this right.
im unclear with your question, Hgy
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| hgy
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optic nerve lesion of one eye will lead to loss of the direct pupil reflex of the lesion eye and indirect pupil reflex of the fellow eye. e.g., if left optic nerve is injured such as by traucoma or optic nerve neuritis, the ldirect pupil light reflex of left eye is lost and indirect light pupil reflex of the right eye is lost too.
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| ssrpk
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Galaxum wrote:
_ So, when chiasm is affected, it means that both optic nerve cant conduct the signal, then light reflex will be lost.
hi galaxum,
well lesions involving the optic chiasm affects the crossing fibers from the temporal visual fields; pupillary light reflexes depends upon the intensity of the light falling on the retina, which can be transmitted from nasal hemifields as well ; therefore loss of pupillary light reflexes will not be a feature of injury to optic chiasm!
besides, the consensual light reflex is due to fibers from pretetal nucei crossing in the posterior commissure!
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| Galaxum
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You are right ssrpk,
pupillary light reflexes depends upon the intensity of the light falling on the retina, which can be transmitted from nasal hemifields as well ; therefore loss of pupillary light reflexes will not be a feature of injury to optic chiasm!
So you have a special situation of total copression or destruction of chiasm where you will loss the reflex.
Hgy,
I would like to discuss in this special case.
However, you can deduce the other diseases.
optic nerve lesion of one eye will lead to loss of the direct pupil reflex of the lesion eye and indirect pupil reflex of the fellow eye. e.g., if left optic nerve is injured such as by traucoma or optic nerve neuritis, the ldirect pupil light reflex of left eye is lost and indirect light pupil reflex of the right eye is lost too.
You are correct. a little bit more in this case, if right part and left iris are normal, then we can see the right direct reflex and left indirect reflex theorically. Inspite of visual loss in left eye  ....
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| hgheith
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So what is the correct answer? I agree that a lesion of the visual radiations would cause a homonymous Quadrantanopia.
with the pupilary light reflex a good way to remember is " in on II out on III" the afferents being CNII and efferents CNIII. So if there was a lesion to the optic nerve on one side first you would get monocular blindness, and if you shine a light in the bad eye nothing will happen (no affarent fibers) but if you shine the light in the good eye then both eyes constrict, this is called marcus gunn pupil.
As far as an optic tract lesion goes, you would have a contralateral homonomous hemianopia, I think the pupilary reflex would be ok because the efferents are with CN III, which is not affected in the optic tract lesion, it is still intact. Even if you shine a light in the bad eye, pretectum and the edingerwestfall nucleus project bilaterally, to both eyes, so you would still have a direct and consensual reflex. I think that is what galaxium was trying to say.
My question is that with the optic tract lesion, can afferent still project to the pretectum? would it still reach the EW nucleus?
ssrpk, where is this Q from? does it come with an explanation?
thank you
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| ssrpk
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this q is from usmle roadmap neuroscience.
correct answer is D
lesion s proximal to lat. geniculate body will affect light refelxes while lesions distal to thalamus i.e. visual radiations and beyond will not afect light reflexes.
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| hgheith
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Hmm, thanks for the reply, but every book I looked in said a lesion in the visual radiations would lead to a homon. quadrantanopia. 
If anyone knows about how the info projects after it crosses the chiasm, I would really like to know, is it bilateral, contralateral only or ipsilateral only?? If it was bilateral then it would make sense that the pupillary reflex would be intact in an optic tract lesion, if not, then we have a problem!
Thanks for the review though!
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| ssrpk
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well..... some nfo distal to chiasm is from the contralateral retina (temporal half of visual field) and some are ipsilateral (nasal half of visual field)
except for meyer's loop the rest of visual radiuations are supplied by the branches of posterior cerebral artery ; so follwoing strokes involving PCA it may causae contralateral homonymous hemianopsia or even quadrantanopsia, depending upon the extent of involvement!
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