Pupil disorders Flashcards
Define Mydriasis and its physiology.
- Dilated pupil
- Circular muscles in iris – cause pupil constriction. Stimulated by parasymp NS along oculomotor nerve using Ach.
Causes of mydriasis.
- Third nerve palsy
- Holmes-Adie syndrome
- Raised intracranial pressure
- Congenital
- Trauma
- Stimulants such as cocaine
- Anticholinergics
Define miosis and its physiology.
Constricted pupil.
- Dilation muscles extend radially (outwards from center) through iris. Stimulated by symp NS using adrenaline.
Causes of miosis.
- Horners syndrome
- Cluster headaches
- Argyll-Robertson pupil (in neurosyphilis)
- Opiates
- Nicotine
- Pilocarpine
Define 3rd nerve palsy.
- Lack of function (palsy) of CN III = Oculomotor nerve.
Causes of 3rd nerve palsy.
- 3rd N palsy which spares pupil (parasymp fibres are spared) caused:
o Diabetes
o HTN
o Ischemia - Full 3rd nerve palsy = compression of nerve (aka surgical third) causes:
o Tumor
o Trauma
o Raised ICP
o Oculomotor nerve travels through cavernous sinus and close to post comm A – so cavernous sinus thrombosis or PSA aneurysm can compress nerve and cause palsy.
o Idiopathic
How does 3rd nerve palsy present? Explain why these symp occur.
ptosis, dilated non reactive pupil and divergent strabismus (down and out position).
- Oculomotor nerve supplies all extraocular muscles except lateral rectus and sup oblique.
- Therefore when extraocular muscles are not receiving signals from oculomotor N – eyes move outwards and downwards due to effect of lateral rectus and sup oblique working without resistance.
- Oculomotor nerve also supplies levator palpebrae superioris – lifts up upper eyelid – therefore in third nerve palsy – ptosis.
- Oculomotor nerve also has parasymp fibers that innervate sphincter muscles of iris – therefore get dilated fixed pupil.
- Double vision
How is third nerve palsy diagnosed?
- neuro exam.
- CT/ MRI brian to find cause.
How is 3rd nerve palsy Mx?
Mx cause.
Define Horner’ syndrome
- Damage to symp NS supplying face (one side).
Pathophysiology of horner’s syndrome?
damage to oculosympathetic pathway
o Damage to 1st order neuron = lesion above T1 – stroke, tumors, syringomyelia (cyst/ cavity in spinal cord).
o Damage to 2nd order neuron – Pancoast tumor
o 3rd order neuron – dissection of int carotid A
How can we locate where damage in Horner’s is given the symp?
determined by anhydrosis.
- Central lesion = 1st order lesions = cause anhidrosis of arm, trunk and face,
o Pre ganglionic lesions = 2nd order lesions – anhidrosis of face
o Post ganglionic lesions = 3rd order lesions – DON’T cause anhidrosis.
RF for Horner’s syn?
- Birth trauma (neck trauma at birth).
- Congenital Horner syn – associated w. heterochromia
define heterochromia.
diff colour eyes.
How does Horner syn present
ipsilateral side as damage.
SPAM (symp NS, ptosis, anhydrosis and miosis).
enophthalmos
How are light and accommodation reflexes affected in horner’s?
not affected - stay normal.
how is Horner’s syn diagnosed?
- Eye drop test that contains cocaine or apraclonidine.
- CT/ MRI for underlying cause – dissection, malignancies etc.
Why is cocaine and apraclonidine used to diagnose horners?
o Cocaine blocks reuptake of NA (symp neurotransmitter) – therefore NA will build up and cause pupil to dilate.
o If there is a block to symp innervation – there will be no NA – therefore no pupil dilation.
o Apraclonidine is a weak form of NA. normally apraclonidine is too weak to cause dilation, but when there is a block of symp innervation the pupil dilatory muscles becomes so starved of innervation that it causes eye to dilate.
Mx of horners syndrome?
- Mx cause.
- Surgery for syringomyelia, tumors, carotid A dissection.
Define holme Adie.
- Unilateral dilated pupil (benign and dilation starts at early stages – pupil gets smaller over time).
- Pupil reacts slowly to light BUT quickly to accommodation = light-near dissociation.
Pathophysiology of holme Adie.
- Damage to post ganglionic parasymp fibres by viral or bacterial infection, e.g HZV.
RF for holme adie?
- Young women (3-40 yrs)
Presentation of holme adie?
- Small pupil – will get smaller over months to yrs.
- Light-near dissociation.
What is holme adie syn?
- Holmes Adie Syndrome = Holmes Adie pupil w/ absent ankle and knee reflexes.
Mx of holme adie
- Refer children < 1 yrs.
- Corrective glasses.
