the pupil - medicinebau.com · because of its extended course , the sympathetic pathway may be...
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The pupil Done by Nebras abu abed
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Pupillary responses
Responeses :
1) response to light
2)accommodation for near vision (near response )
These reactions are performed by reflex arcs with afferent and efferent
limbs :
1)Afferent : simply by the optic nerve
2)Efferent : by sympathetic and parasympathetic
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More light through optic nervepretectal nucleusedinger-westphal
nucleus preganglionic parasympathetic fibres carried by oculomotor
nerve ciliary ganglion postganglionic parasympathetic fibres (short
ciliary nerves ) to pupilloconstrictor smooth muscle fibres miosis .
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Less light through optic nerveoptic tract pretectal nucleusedinger-
westphal nucleus to hypothalamus to ciliospinal centre in C8, T1 & T2
Preganglionic sympathetic fibres to superior cervical ganglionpost
ganglionic fibres around ICA trigeminal nerve ophthalmic
nervenasociliary nerve long ciliary pupillodilator muscle mydriasis .
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Disorders of pupillary function
May result from :
1)Ocular disease
2)Disorders of afferent and efferent controlling pathways
3)Drugs !!!
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1)Ocular diseases
Anterior uveitis if it caused post synechiae…it will give the pupil an irregular
appearance .
Can result from intraocular surgery
Blunt trauma to eye
In acute close angle glaucoma
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2)Controlling pathways
Lesions of pupillary pathways can be broadly classified into afferent and
efferent defects .
Affernet defects can be either complete or incomplete(hence the name
relative afferent pupillary defect )
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Efferent(c,d) and complete afferent(a,b)
defects
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Relative afferent pupillary defect
Best detected by swinging light torch : light is repeatedly shone into the
affected eye alternating with the good side . When the light is shining on
the unaffected eye , both pupils constrict . When it’s transferred to the
diseased side , there is bilateral pupillary dilation .
Seen in optic nerve lesions such as optic neuritis and may be seen in very
severe disease of retina but not with opacities of the cornea or lens .
https://www.youtube.com/watch?v=HSYo7LhfV3A
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Horner syndrome
It arises from lesions affecting the sympathetic efferent pathway which will
cause :
1)Miosis : results form loss of dilator function
2)Ptosis : muller muscle is affected
3)Enophthalmus : the reduced palpebral aperture size gives an impression of
recession .
4)Anhydrosis , if the sympathetic pathway is affected proximal to the base of
skull .
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Because of its extended course , the sympathetic pathway may be
affected by multiple pathologies , examples :
1) Syringomyelia , an expanding cavity within the spinal cord, sometimes
extending into the medulla (syringobulbia), which compresses the
pathway. Typically, it also causes wasting of the hand muscles and loss of
sensation.
2) Small-cell carcinoma at the lung apex which catches the cervical
sympathetic chain. Involvement of the brachial plexus gives rise to pain
and to T1 wasting of the small muscles of the hand in Pancoast’s syndrome.
3) Neck injury , disease or surgery .
4) Cavernous sinus disease , it affects the sympathetic plexus around ICA
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Light-near dissociation
Impaired reaction of pupils to light , while the near response to
accommodation is retained . Seen in :
1)Argyll roberston pupil .
2)Midbrain pupil .
3)DM & multiple sclerosis .
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1)Argyll Roberston pupil
The pupils are bilaterally small and irregular .
Accommodate but don’t react to light at all .
Classically seen in neurosyphilis , it’s suggested that a periaqueductal lesion
on dorsal aspect of edinger-westphal nucleus involves fibres associated
with response to light but spares those associated with near response .
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Adie’s tonic pupil
It’s due to ciliary gangilionitis which results in partial parasympathetic denervation of iris with resultant upregulation of its muscarinic receptors…
The consequences are
1)Unilateral enlarged pupil that can become bilateral overtime .
2)Poor reaction to light with characteristic slow , worm-like(vermiform) contraction of iris .(sectoral paresis)
3) Slow sustained miosis on accommodation(hence the name tonic) , results from muscarinic supersenitivity .
4)Constricts to dilute pilocarpine (0.1%),unlike the normal pupil .
5) Can be part of bigger syndromeadie-holmes syndromeAreflexia .
The ciliary body is nine times more innervated than iris so it isn’t affected as the iris .
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Adie’s Argyll
unilateral bilateral
ciliary ganglionitis periaquidectal lesion
mydriasis & regular miosis & irregular
slow & sluggish light reflex absent light reflex
Tonic miosis on accommodation normal accomodation
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2)Midbrain pupil
Arises from lesions affecting the pretectal nuclear complex in dorsal region of midbrain produces mydriasis and light near dissociation .
Causes include demyelination , infarction , enlargement of 3rd ventricle and
space occupying tumors such as pineloma .
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3)Drugs
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Other causes of pupillary abnormalities
In coma, both pupils may become miosed with preservation of the light
reflex if a pontine lesion is present, but remember that patients taking
pilocarpine for glaucoma or receiving morphine also show bilateral miosis.
Midbrain lesions cause loss of the light reflex with mid-point pupils. Coma
associated with a unilateral expanding supratentorial mass, e.g. a
haematoma, results in pressure on the third nerve and dilation of the pupil.
Intrinsic third nerve (Parasympathatic) lesions also cause a dilated pupil.
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Let’s do some questions
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