ANATOMY - Pupil and Pupillary pathways (reflexes)

Question 1

What is simple anisocoria?

Answer 1

<0.4mm difference in pupil size - present in 25% of the population and may change sides.

Question 2

What is physiological tremor in pupil known as?

Answer 2

Hippus (pupillary athetosis)

Question 3

What is physiological anisocoria?

Answer 3

When the difference in size is usually 1mm in diameter or less
1. pupil size disparity is same in the light as in the dark
2. pupils react normally to light.

Question 4

If anisocoria is greater in the light, which pupil is abnormal?

Answer 4

the larger pupil, the pupil which failed to constrict.

Question 5

What are the causes of abnormally dilated pupil (ie greater anisocoria in the light?) (4)

Answer 5

1. Traumatic iris sphincter muscle - torn pupillary margin or iris transillumination defects.
2. Adie Tonic pupil - irregular pupil, reacts minimally to light, and slowly to convergence. Hypersensitivity to pilocarpine 0.125%.
3. Third nerve palsy - always associated ptosis or extraocular muscle palsies
4. Mydriasis drops

Question 6

If anisocoria is greater in the dark, which pupil is abnormal

Answer 6

Smaller pupil (pupil fails to dilate).

Question 7

What are the causes when abnormal pupil is constricted?

Answer 7

1. Uveitis
2. Horner syndrome - mild ptosis on side of small pupil
3. Argyll Robertson pupil - bilateral irregularly round miotic pupils but mild degree of anisocoria
4. Pharmacological miosis

Question 8

What scenarios does mydriasis occur in ?

What scenarios does miosis occur in? (3)

Answer 8

Mydriasis: low light, excitement, fear

Miosis: illumination, convergence, sleep.

Question 9

What are the effects of pupillary dilation? (5)

Answer 9

1. Reduces depth of field
2. Reduces depth of focus
3. Reduced diffraction of light
4. Increased Stiles-Crawford Effect
5. Increased chromatic aberration

Question 10

What is the Stiles-Crawford Effect?

Answer 10

Light entering the edge of the pupil is less effective at stimulating photoreceptors than light entering centrally because it meets the receptors obliquely rather than axially.

Question 11

What is the difference between Stiles-Crawford effect 1 and Stiles-Crawford effect 2?

Answer 11

effect 1 - greater stimulus effectiveness (brightness) of a ray passing paraxially compared to a ray entering eccentrically.

effect 2: change in hue and saturation of monochromatic light depending on angle of incidence

Question 12

What is the latency period of the pupil?

Answer 12

Duration from exposure to response - on average 0.2-0.5 seconds

Question 13

What is the latency period affected by? (2)

Answer 13

1. Light intesity - decreases with increasing light intensity
2. Accomodation (pupil reacts faster to light than to accomodation)

Question 14

What is pupil size affected by? (2)

Answer 14

1. Iris colour (blue larger than brown)
2. Autonomic nervous system (fatigue, exercise, light intensity)

Question 15

What are the two types of light reflex?

Answer 15

1. The direct pupillary reflex
2. Consensual pupillary reflex

Question 16

What is the afferent pathway of the light reflex?

Answer 16

FROM RETINA TO PRETECTAL NUCLEUS

1. Fibres leave tract and synapse in pretectal olivary nucleus near superior colliculus
2. Each pretectal nucleus only receives ipsilateral input.

Question 17

What are the 3 pathways of the light reflex?

Answer 17

1. Afferent (from retina to pretectal nucleus)
2. Internuncial neuron/centre (from pretectal to edinger westphal nucleus)
3. Efferent (from edinger westphal, third nerve, ciliary ganglion and short ciliary nerve to sphincter pupillae)

Question 18

What is the role central pathway of the light reflex? (internuncial neurons)

Answer 18

1. Axons from pretectal nucleus nerve cells will cross/synapse towards the edinger westpal nucleus (parasympathetic) of the oculomotor nerve on BOTH sides of the midbrain
2. Each prectal nucleus will give fibres to both edinger westphal nuclei –> this is responsible for the direct AND consenusal reflex.

Question 19

What is the efferent pathway of the light reflex?

Answer 19

1. Preganglionic fibres travel with oculomotor nerve (through its inferior division to inferior oblique) to ciliary ganglion and synapse
2. Postganglionic fibres travel in short ciliary nerves to sphincter pupillae muscle and both pupils constrict.

Question 20

What are the causes of an efferent pupillary defect (fixed dilated pupil) (6)

Answer 20

1. Brain stem lesions at level of superior colliculus and red nucleus (accompanied by long tract signs
2. Third nerve lesions, usually compressive (20% of microvascular palsies involve the pupil)
3. Ciliary ganglion/short ciliary nerve lesions
4. Iris damage due to surgery
5. Grossly elevated IOP
6. Mydriatic drugs –> pilocarpine will only constrict a pupil affected by a neurological lesion)

Question 21

What conditions can cause RAPD? (3)

Answer 21

LESIONS OF RETINA
1. Large retinal detachments
2. Ischaemia (CRVO/CRAO)
3. Dense Macular Lesion

LESIONS OF ANTERIOR OPTIC PATHWAY (retina to pretectal nucleus)
1. Lesions of optic nerve (optic neuropathy, glaucoma)
2. Lesions of optic chiasm
3. Lesions of optic tract
4. Lesions of pretectum

Question 22

Which areas of visual pathway would not be affected by RAPD?

Answer 22

1. Lateral geniculate body
2. Optic radiations

Question 23

What happens to the affected eye when there is RAPD in light swinging test?

Answer 23

Paradoxical dilatation of affected eye, also of consensual eye.

Question 24

What is Reverse RAPD?

Answer 24

Used to test efferent defects

Paradoxical dilatation ONLY in CONSENSUAL EYE as AFFECTED eye is FIXED DILATED –> means there is RAPD in fixed dilated eye.

Paradoxical dilatation occurs as does not receive light input from AFFECTED eye for consensual light reflex.

Question 25

What is wernicke's hemianopic pupil?

Answer 25

It is an AFFERENT PUPILLARY DEFECT with a lesion in the OPTIC TRACT which presents with contralateral hemianopia

Question 26

What is the pathology of Argyl Robertson Pupil?

Answer 26

Lesion in the internucial neurons of the light pathway (in the midbrain) --> specifically the DORSAL (posterior) aspect of the edinger westphal nucleus

Question 27

What is the argyl robertson pupil?

Answer 27

It is smaller, irregular in shape, Little to no constriction to light (absent light reflex) and BRISK near reflex ARP --> Accomodation reflex present PRA --> pupillary reflex absent

Question 28

Why are the argyl robertson pupils miotic?

Answer 28

There is disruption of the supranuclear/dorsal adrenergic fibres that inhibit the edinger westphal nucleus therefore... uninhibited parasympathetic neurons of edinger westphal nucleus leads to miosis (spinal miosis)

Question 29

What are the causes of argyll robertson pupil?

Answer 29

Diabetes Neurosarcoidosis MS Lyme Disease Encephalitis Chronic alcoholism Tertiary neurosyphilis

Question 30

What is Adie Tonic Pupil (Holmes-Adie Syndrome)

Answer 30

It is parasympathetic denervation of the pupil which causes poor/absent light reflex but with near reflex present (tonic reaction) Adie tonic pupil + decreased deep tendon reflexes

Question 31

What is the cause of adie tonic pupil?

Answer 31

Damage to ciliary ganglion --> upregulation of postsynaptic receptors to allow re-innervation --> abnormal/abberant innvervation/regeneration --> tonic miosis on near reflex along with accomodation.

Question 32

How do you diagnose adie tonic pupil?

Answer 32

Anisocoria, worsening of anisocoria in light. Responds supersensitive to 0.125% diluted pilocarpine --> after 30-60 minutes the dilated pupil will now constrict more than the normal pupil This is because of increased receptors due to denervation hypersensitivity.

Question 33

What is the difference between argyll robertson pupil and adie tonic pupil?

Answer 33

Both have light-near dissociation, but argyll robertson the pupil is smaller, in Holmes/Adie the pupil is larger.

Question 34

What are the three main types of aetiologies of Horner's syndrome?

Answer 34

1. Central brainstem lesions (First Order - neuron from hypothalamus terminating at ciliospinal centre of budge) 2. Preganglionic lesions 3. Post-ganglionic lesions

Question 35

What are the first order causes of Horner's syndrome? (7)

Answer 35

1. CVA 2. Lateral Medullary Syndrome 3. Arnold-Chiari malformation 4. Encephalitis/Meningitis 5. Syringomyelia 6. Intracranial tumors (pituitary or basal skull) 7. Spinal trauma above T2/T3

Question 36

What are the pre-ganglionic (second order) causes of Horner's syndrome (7)

Answer 36

From the ciliospinal centre of budge to the superior cervical ganglion at C3/C4 level. 1. Pancoast tumour (malignancies) 2. Subclavian artery lesions 3. Cervical rib injuries 4. Mediastinal lymphadenopathy 5. Trauma of branchial plexus 6. Dental absess involving mandibular region 7. Iatrogenic - thyroidectomy, CABG

Question 37

What are the post-ganglionic (third order) causes of Horner's syndrome?

Answer 37

From superior cervical ganglion --> V1 of trigeminal nerve --> long ciliary nerve --> sphincter dilator muscle and superior tarsal muscle and sweat glands. 1. Carotid cavernous fistula 2. Internal carotid artery dissection / aneurysm 3. Cluster headache/migraine 4. Herpes zoster infection 5. GCA 6. Raeder paratrigeminal syndrome (unilateral facial pain) 7. Cavernous sinus thromboss

Question 38

What are the signs of Horner's syndrome?

Answer 38

Miosis - reaction of pupils to light and accomodation is normal Ptosis - partial due to muller's muscle involvement and reverse ptosis (lower lid involvement) Anhidrosis- First order neurons (full body), second order (face), third (ipsilateral brow)

Question 39

When is cocaine used for pharmacological test for Horner's syndrome? What is the mechanism?

Answer 39

For all 1st/2nd/3rd order neurone testing to confirm horner's --> there is an EXAGERRATION OF ANISOCORIA. Prevents reuptake of noradrenaline from synapse --> in all 1st/2nd/3rd order cases there is no noradrenaline in the synapse so cannot act therefore Horner pupil does not dilate and normal pupil dilates.

Question 40

When is apraclonidine 0.1% used in testing Horner's syndrome?

Answer 40

causes REVERSAL OF ANISOCORIA --> Horner's pupil dilates and normal pupil does not dilate. A2-agonist and weak A-1 agonist --> due to sympathetic denervation --> there is hypersensitivity of A1-Receptor within pupillary dilator muscle to cause DILATATION. Should not be used in paediatrics due to risk of CNS/respiratory depression.

Question 41

When is Hydroxyamphetamine 1% test used in Horner's syndrome?

Answer 41

THIRD ORDER NEURON - no response 1ST/2ND - the Horner pupil dilates. Hydroxyamphetamine 1% Releases stored noradrenaline from the third-order neuron pre-synaptic terminal within the iris --> increased dilatation (1st/2nd order) In 3rd-order neuron, there is a lesion in this neuron, so there is no stored noradrenaline so there is no pupillary response to hydroxyamphetamine drops.

Question 42

When is phenylephrine used in Horner's syndrome?

Answer 42

to confirm location of Horner's syndrome. adrenergic agonist --> acts on hypersensitive A-1 receptors so will see dilatation of pupil (in THIRD-ORDER neuron) There is no denervation hypersensitivty in 1st/2nd order neuron so no dilatation of pupil with phenylephrine

Question 42

Whats the difference between argyll-robertson pupil and Adie pupil?

Answer 42

Argyll pupil is small, unresponsive to light, Adie pupil is large, slow responsive to light. Both pupils have strong near reponse. Argyll robertson has associated with absent tendon reflexes and iris atrophy.