pupils Flashcards
how are the pupils innerveated (parasympathetically)
The pupil constricts by contraction of the sphincter pupillae muscle, which is controlled by innervation by the parasympathetic fibres in the 3rd cranial nerve
The neurotransmitter is acetylcholine
Acetylcholine binds to muscarinic cholinergic receptors
Pupil size is predominantly controlled by parasympathetic tone
how are the pupils innervated sympathetically
The pupil dilates by contraction of the dilator pupillae muscle, which is controlled by innervation from sympathetic fibres carried to the eye via blood vessels
The neurotransmitter is noradrenaline
Noradrenailne binds to alpha receptors
describe the pupil reflexes
The pupil has three reflexes
Reaction to light (constriction-miosis)
To direct illumination in one eye
To consensual illumination in the fellow eye
Reaction to dark (dilatation-mydriasis)
Reaction to a near target
Miosis
Accommodation (focussing by ciliary muscle)
Convergence
describe the mechnaissm of the light reflex
Light enters the eye and stimulates the retina
Impulses pass to both optic tracts at the chiasm
Afferent limb ends at the parasympathetic part of the 3rd nerve nucleus (Edinger-Westphal)
Efferent impulses pass along 3rd cranial nerve
Fibres synapse in ciliary ganglion in orbit
Pupil constriction occurs in both eyes by stimulation of sphincter muscle
What are the key components and mechanisms involved in the control of pupil size?
Sphincter muscle (cholinergic, IIIn): Responsible for constriction of the pupil. It is innervated by the parasympathetic nervous system via cranial nerve III (oculomotor nerve).
Dilator muscle (noradrenergic, sympathetic): Responsible for dilation of the pupil. It is innervated by the sympathetic nervous system.
Afferent limb: Involves the pathway of sensory input. It includes the retina, optic nerve, optic chiasm, and optic tract.
Central integration: The integration of sensory input and generation of appropriate motor responses. It occurs in the mesencephalon and involves the Edinger-Westphal nucleus (E-W nucleus).
Efferent limb: Involves the pathway of motor output. It includes cranial nerve III (oculomotor nerve) and the sphincter muscle for pupil constriction.
how to check pupil reactions
Check that pupils react to light:
Shine into left eye and observe left eye
Shine into left eye and observe right eye
Shine into right eye and observe right eye
Shine into right eye and observe left eye
Check pupils react to a near target
if you are asked to examine the patients pupils what should you do
Anisocoria (pupils are different sizes)
Afferent pupillary defect (problem in the retina or optic nerve)
Efferent pupillary defect (problem with the 3rd nerve or sphincter muscle)
Light near dissociation (poor or absent response to light but a normal response to near)
what is the direct and consensual papillary refelx
shine the light from your pen torch into patietns pupil to observe for pupillary reaction
a normal direct pupillary reflesx involves constriction of the pupil that the light is being shone into
consensula shine light into one pupil observe pupil constrictiion in the other eye
what does the swinging light test asess
Direct the light from the flashlight into one eye while observing the response of both pupils. Note the initial size and reaction of the illuminated pupil.
Quickly move the light to the other eye, shining it into that pupil while observing both pupils simultaneously.
Repeat this process, swinging the light back and forth between the two eyes several times.
Observations: During the swinging of the light:
Normal Response: Both pupils should constrict briskly when illuminated and dilate when the light is removed.
Abnormal Response (RAPD): In a patient with RAPD, the affected pupil may paradoxically dilate (or fail to constrict as briskly) when the light is swung to that eye. This is because the affected eye is less responsive to light due to a defect in the afferent visual pathway.
what do the different pupillary tests assess
The direct pupillary reflex assesses the ipsilateral afferent limb and the ipsilateral efferent limb of the pathway.
The consensual pupillary reflex assesses the contralateral efferent limb of the pathway.
The swinging light test is used to detect relative afferent limb defects.
what pathologies may the different pupillary tests pick up
Direct Pupillary Reflex:
Ipsilateral Afferent Limb: This part of the pathway involves the sensory input from the retina to the brainstem. Abnormalities in this limb may indicate dysfunction in the retina, optic nerve, optic chiasm, or optic tract on the same side as the stimulated eye. Conditions affecting these structures include optic neuritis, optic nerve compression (e.g., from a tumor), or ischemic optic neuropathy.
Ipsilateral Efferent Limb: This part involves the motor output from the brainstem to the sphincter muscle of the iris on the same side. Dysfunction in this limb may indicate pathology affecting cranial nerve III (oculomotor nerve) or the Edinger-Westphal nucleus in the midbrain. Causes may include oculomotor nerve palsy, midbrain lesions, or compression of cranial nerve III.
Consensual Pupillary Reflex:
Contralateral Efferent Limb: This limb involves the motor output from the brainstem to the sphincter muscle of the iris on the opposite side. Abnormalities in this limb may indicate dysfunction affecting the contralateral side of cranial nerve III or the Edinger-Westphal nucleus. Causes may include lesions or compression affecting the contralateral oculomotor nerve or midbrain structures.
Swinging Light Test (Relative Afferent Pupillary Defect - RAPD):
Relative Afferent Limb: This test is specifically designed to detect defects in the afferent limb of the pupillary pathway. It assesses the response of both pupils to a swinging light stimulus. A relative afferent pupillary defect (RAPD) indicates decreased or impaired pupillary constriction in response to light in one eye compared to the other. This defect suggests dysfunction in the afferent visual pathway of the affected eye, typically before the optic chiasm. Causes may include optic neuritis, optic nerve ischemia, retinal disorders, or optic nerve compression
afferent puillary defect affecting the right eye would present as
Caused by a problem in the retina or optic nerve of the right eye, for eg.
Pupils equal in size before illumination
Neither pupil responds to stimulation of right eye
Both pupils respond to stimulation of left eye
Both pupils react to near stimulation
what might an efferent pupillary defect affecting the right eye cause
Caused by a problem with the 3rd nerve or sphincter muscle
Right pupil will usually be larger than the left pupil
The right pupil will not respond to either eye being illuminated
The left pupil reacts to illumination from either eye
what are the causes of an anisocoria
Physiological (a difference of 1-2mm, normal reactions)
Horner’s syndrome (smaller pupil, ptosis)
Adie’s pupil (larger pupil, efferent defect)
III n palsy (larger pupil , efferent defect, ptosis, divergent eye)
Drugs
Pilocarpine (makes the pupil smaller)
Atropine (makes the pupil larger)
Iris damage (glaucoma, iritis, surgery, trauma)
what would you see in horners syndrome: oculo- sympathetic paralysis
Physiological (a difference of 1-2mm, normal reactions)
Horner’s syndrome (smaller pupil, ptosis)
Adie’s pupil (larger pupil, efferent defect)
III n palsy (larger pupil , efferent defect, ptosis, divergent eye)
Drugs
Pilocarpine (makes the pupil smaller)
Atropine (makes the pupil larger)
Iris damage (glaucoma, iritis, surgery, trauma)
what is the cocaine test in horners
Cocaine is an indirect sympathomimetic
It prevents the re-uptake of noradrenaline
In a normal eye, cocaine dilates the pupil
In Horners, the pupil fails to dilate as no noradrenaline
what are the courses of horners syndrome
A right sided Horner’s syndrome is caused by a lesion on the right side
Horner’s caused by brainstem and spinal lesions is associated with other neurological problems e.g. brainstem stroke
Apical lung lesions e.g. Pancoast’s tumour, cervical rib
Neck surgery e.g. thyroidectomy
Internal carotid artery dissecting aneurysm
Cavernous sinus and orbital disease
Headache syndromes: cluster headaches, Raeder’s paratrigeminal neuralgia
what are the investigations of a horners syndrome
If a patient develops a recent onset Horner’s syndrome
Examine for other neurological signs
CXR especially if the patient smokes and has arm/hand pain or wasting
Carotid artery dissection must be considered if there is neck pain and a history of neck trauma
what is adies pupil
Adie’s pupil is caused by parasympathetic denervation
The signs are:
Mydriasis (dilated pupil) with poor or absent response to light
Reduced accommodation (blurred vision when reading)
Light near dissociation
After several years the pupil often becomes smaller
There is no serious underlying neurological problem
n
what are the signs of a third nerve palsy
The signs are:
A dilated, un-reactive pupil (not all cases)
Ptosis (not always complete)
Divergent eye (action of the lateral rectus)
Important causes are:
Diabetes/vascular disease
Often the pupil is not involved
Full recovery can occur
Compression
Posterior communicating artery aneurysm
uncal herniation due to intracranial haemorrhage after trauma
Early diagnosis is essential
further investigations for a third nerve palsy
A painful third nerve palsy must have urgent scan to look for posterior communicating artery aneurysm as can be life threatening.
3rd nerve plasy possible signs in a R third
Right sided 3rd n palsy
Pupil fixed and dilated
Ptosis
Divergent eye
Angiography show a PCA aneurysm
Anisocoria other causes
Damage to the iris by acute angle closure glaucoma and therapeutic laser can lead to a fixed, mid-dilated pupil
Iritis can cause the pupil to become stuck to the lens causing an unreactive irregular pupil.
what are the causes of a RAPD
Problems with the afferent limb of the pupil light reflex pathway will lead to a RAPD
Causes are:
Large retinal lesions e.g. Retinal detachment, ischaemic central retinal vein occlusion, central retinal artery occlusion
Optic neuropathies e.g. advanced glaucoma , optic neuritis, anterior ischaemic optic neuropathy
Best detected using swinging torch test
what would you find in a right sided RAPD
This test is performed by swinging a torch from one eye to the other, illuminating each eye for about 2 seconds
Observe the eye that is being illuminated
Stimulation of left eye causes pupil constriction
When the torch is moved to the right eye the pupil paradoxically dilates
This is a very sensitive and specific test for optic neuropathy affecting one eye
The RAPD is lost if optic neuropathy is bilateral
what happens in adies pupil vs horners
in horners pupil wont dilate
adies - pupil wont constrict
what is adies pupil caused by
adies pupil is caused by parasy,mpathetic dysinnervation
no seroious neruoloigcal
after few years pupil becomes smallerf
features of adies
caused by parasympathetic dennervation
mydriassis - poor /absent response to light
reduced asscomdation
light near disscoation
what should you examine in a recent onsent horners
examine for other neuro signs
cxr if pt smokes
carotid artery diesae if neck metnioned
uncal herniation
early diagnosis is essential
causes and presentation of a third nerve palsy
compression of the pca
dlated unreactive pupil
ptosis not always complete
causes - diabetes . vascular disease , full recovery can occur
causes for RAPD
optic neuropathies
advanced glaucoma
optic neuritis
large retinal lesions
e.g. retinal dettachemtn
CRA
iritis
pupil can be stuck to the lense
casuing unreactive irregular pupil
causes for rapd
problems with afferent limb of the pupil
light travelling to the brain (pretectal nucelus of the brain)
optic neuropathies
advanced glaucma
optic neuritis
large retinal lesions e.g. retinal dettachemnt
CRA
best detected using swing test
aag and anisocoria
tells you that their has been damage to the iris by aag therapeutic laser
mid dilated pupil
causes of anioscoria
physicological 1-2mm normal
horners syndrome (smaller pupil, ptosis)
adies pupil ) larger pupil , ptosis
3rd nerve palsy
larger pupil efferent affect ptosis
divergent eye
drugs that affect the pupil
pilocarpine makes the iris smaller
atropine makes the pupil larger
what efferent pupillary defects affecting the RE
caused by problems with the third nerve on the sphinicter muscle
right pupil will be larger than left
right will not respond to etiher from left
left pupil reacts to illumination from either eye
horners syndrome causes
miosis
mild ptosis
normal light and near response
sometimes facial anhydriassi
causes - brainstem + spinal causes
carvernous sinus or orbital disease
symptoms = cluster headahces
cocaine test can be done - pupil wont dilate
fails to dilate as no anhydriasis
causes of horners syndrome
causes : pancoast tumour
neck sx= thyroidectomy
if pupil larger in sunlight
pathological eye is the one that is bigger - pupil should constrict in the sunlight
should constrict in sunlight
if difference in pupil is more accenuated in the dark then pathological one is the smaller pupil
examples of pathology causing an anisoria in sunlight
third nerev plsy
example of pathology casuing more of a pronounced anisocira in the dark
horners syndrome , sympathetic pathway affecting dialtor pupillae
abnormal pupils coould. also be to conditons such as posterior synachie
what happens in a rapd and why
when afferent limb is damaged both pupils will cnstrict less
both pupils constrict less when light is shone into the affceted eye compared to the healthy eye
pupils therefore appear relativley dilate
can be due to retinal damage in affected eye
can be due to CRA, CVO secondary to tumour
