3.1.9: Assess pupil reactions

Question 1

What is afferent and efferent pathways?

Answer 1

• Afferent: Nerve that carries information towards the central nervous system
• Efferent: Nerve that carries information away from the central nervous system

Question 2

What is sympathetic and parasympathetic?

Answer 2

• Sympathetic: Fight or Flight
• Parasympathetic: Rest & Digest

Question 3

What is cholinergic and adrenergic?

Answer 3

• Cholinergic Receptors (muscarinic): Stimulated by acetylcholine
• Adrenergic Receptors (alpha-1): Stimulated by noradrenaline

Question 4

Describe the sphincter muscle?

Answer 4

Pupil size is mainly determined by the contraction & relaxation of the sphincter
muscle.
-> It is a thin circumferential ring of smooth muscle fibres
* The sphincter muscle responds to signals from the short ciliary nerve
Þ This constricts the pupil
* The sphincter muscle is innervated by cholinergic parasympathetic fibres
The Sphincter & Dilator muscles are antagonistic muscles

Question 5

Describe the dilator muscle?

Answer 5

• The dilator muscle has a secondary effect on pupil size
• The dilator muscle responds to signals coming from the long ciliary nerve
  -> This dilates the pupil
• The dilator muscle is innervated by adrenergic sympathetic fibres
  The Sphincter & Dilator muscles are antagonistic muscles

Question 6

What happens in dark lighting? (pupil)

Answer 6

1. The sphincter muscle relaxes
   -> The sphincter muscle has the biggest effect on pupil size
2. The dilator muscle contracts

Question 7

What happens in bright lighting? (pupil)

Answer 7

1. The sphincter muscle contracts
   The sphincter muscle has the biggest effect on pupil size
2. The dilator muscle relaxes

Question 8

Describe parasympathetic innervation of pupil?

Answer 8

consist of four neurones
o Afferent 1) – Connects the retina with the pre-tectal nucleus at the level of the superior colliculus in the midbrain
o Afferent 2) – Connects the pre-tectal nucleus to BOTH EdingerWestphal nuclei
o Efferent 3) – Connects the Edinger-Westphal nuclei to the ciliary ganglion – parasympathetic fibres pass in to the inferior division of the IIIrd nerve
o Efferent 4) – Leaves the ciliary ganglion and passes with the short ciliary nerves to innervate the sphincter pupillae

Question 9

Describe sympathetic innervation of pupil?

Answer 9

consist of three neurons
o1) – Starts in the posterior hypothalamus and descends down the brain stem to terminate in the cilio-spinal centre
o2) – Passes from the cilio-spinal centre to the superior cervical ganglion in the neck
o3) – Ascends along the internal carotid artery and joins the ophthalmic division of the trigeminal nerve. Sympathetic fibres travel via the nasociliary nerve and the long ciliary nerves until they reach the ciliary body and dilator pupillae

Question 10

Describe the efferent pathway (pupil)?

Answer 10

The efferent pathway carries impulses away from the central nervous system towards the muscles controlling the pupil size:
* Sphincter Muscle – Miosis: Parasympathetic
* Dilator Muscle – Mydriasis: Sympathetic
Sympathetic Branch of the Efferent Pathway
1. Postero-lateral hypothalamus (within the spinal cord)
2. Ciliospinal centre of Budge-Waller (Over the apex of the lung)
3. Superior Cervical Ganglion
4. Travels along the Ophthalmic division of the 5th Nerve (Trigeminal) for a while
5. Long Ciliary Nerve
6. Dilator Muscle
Parasympathetic Branch of the Efferent Pathway
1. Edinger-Westphal Nucleus
2. Cranial Nerve III – (Oculomotor Nerve)
3. Ciliary Ganglion
4. Iris Sphincter Muscle
5. Short Ciliary Nerve
6. Iris Sphincter Muscle
7. Pupil Miosis

Question 11

Describe the afferent pathway (pupil)?

Answer 11

1. Retinal Ganglion Cells
2. Optic Nerve
3. Optic Chiasm
4. Optic Tract
5. Pretectal Nucleus
6. Central Processing Occurs at this point
7. Edinger-Westphal Nucleus
   The afferent pathway travels from the retina to the pretectal nuclei (towards the brain) &
   fibres cross over at the chiasm
   -> A lesion of the optic nerve will likely affect pupil reaction and cause RAPD
   * Light Shone into the Affected Eye will Cause:
   o A reduced direct response
   o A reduced consensual response
   * Light Shone into the Non-Affected Eye will Cause:
   o A normal direct response
   o A normal consensual response

Question 12

Describe the swinging flashlight test and RAPD?

Answer 12

• Swinging flash-light test – Detects relative afferent pupillary defect (RAPD)
  o In dim room lighting – shine the pen torch from below for 2-3 seconds and watch the pupil constrict. Move
  the next eye (within 1 sec) and hold light on fellow eye for 2-3 seconds the pupil should remain constricted or
  dilate and quickly constrict again (if RAPD absent)
  o AN EYE WITH AN RAPD WILL DILATE WHEN THE LIGHT IS HELD OVER IT
• Relative Afferent Pupillary Defect (RAPD) – Presence indicates that a significant area of vision is affected
  o Damage – Retinal layers, the optic nerve, the chiasm, the optic tract, or mid-brain pre-tectal area
  o Never - with cataracts, high Rx, Macular problems
  o Post-chiasmic lesions rarely produce a clinically detectable RAPD
  o Anisocoria is never present with RAPD

Question 13

Describe the near pupil response?
Describe near-light dissociation?

Answer 13

• Near Pupil Responses - Px shifts gaze from the distant target (spot or duochrome) towards a near target (pen tip
  or budgie stick) and back to distant again.
• Near-Light Dissociation – constriction of pupil to near fixation but not direct light
  o Causes – Viral infection (Adie’s tonic pupil), Damaged pre-tectal area (Parinaud’s syndrome), Damage in the
  rostral mid brain (Argyll-Robertson pupil)
  o There is no condition in which the near reflex is defective or lost when the light reflex is normal.

Question 14

Describe absolute pupillary defect (APD)?

Answer 14

Bilateral symmetrical damage to the afferent pathway (between retina and Edinger-Westphal Nuclei) does not produce RAPD
o APD occurs when there has been severe damage to the optic nerve such that the eye is completely blind

Question 15

Describe efferent pupil anomalies? What do they cause? How do they arise?

Answer 15

Cause ANISOCORIA – defects interfere with contraction or dilation of the pupil due to damage - arise from parasympathetic or sympathetic pathways associated with:
o Damage to the parasympathetic (sphincter) nerves that supply the iris
o Damage to the sympathetic (dilator) nerves that supply the iris
o Mechanical hyper-excitation of the sympathetic supply
o Direct damage to the iris sphincter or dilator muscles that results in immobility of the pupil
o Extent depends on the condition of lighting or near effort

Question 16

Describe physiological anisocoria?

Answer 16

20% of population
o Difference is the same in dim and bright light and generally small (<1mm)
o Longstanding with normal near and light response
o Can vary in extent and even reverse (swap eyes)
o When there is a large difference (>1mm) but no difference at different life levels/reflexes are normal

Question 17

Describe pathological anisocoria?

Answer 17

o May be more marked in dim or bright room lighting
o If anisocoria increases in bright light –> parasympathetic problem (IIIrd Nerve Palsy) – Larger pupil affected
o If Anisocoria increases in the dark –> sympathetic problem (Horner’s syndrome) – smaller pupil affected

Question 18

What does damage to the parasympathetic branch of the efferent pathway cause? What do you need to distinguish?

Answer 18

Damage to the parasympathetic arm of the efferent pathway will result in a more dilated
pupil
You need to distinguish if the lesion is:
* Prior to the Ciliary Ganglion
Causing:
- Absent accommodation
- Fixed/Dilated pupils
- Paresis of some of the EOMs
* Post the Ciliary Ganglion
- Post Ciliary Ganglion damage is known as Adie’s Tonic Pupil

Question 18

Describe Adie’s Tonic Pupil (parasympathetic problem)?

Answer 18

Caused by damage to the ciliary ganglion or the postganglionic fibres of the short ciliary nerve (It is a parasympathetic pathway problem).
Results from a disruption of the post-ganglionic supply to the sphincter pupillae.
o Cause – Viral Illness
o Symptoms – Problem with near focussing, blurred distance vision, photophobia, eye pain, headache however
some px may be asymptomatic.
o Signs – Problem with dilation and constriction, reaction to light and accommodation is either reduced or absent, re-dilation of the affected pupil is also slow, segmental damage leads to vermiform movement (movement of non-paralysed iris)
o In longstanding cases pupil can become miotic
o Usually unilateral can be bilateral
o Light-near dissociation develops after 2 months’ dues to nerve regrowth
Characteristics
* Affected eye is dilated
* Pupil reacts poorly to light (poor direct & consensual response)
* Near reaction is strong, slow & tonic
* When the patient re-fixates at a distance, the pupil re-dilates very slowly
* Maximum response to Pilocarpine

Question 19

Describe IIIrd CN palsy with pupil involvement (parasympathetic problem)?

Answer 19

– lesion that compresses the third CN supply and also compresses parasympathetic nerve fibres which travel along its surface
o Signs – Complete Ptosis, Diplopia, Hypotropia and Exotropia, restricted parasympathetic supply inhibits
constriction, extent of Anisocoria increases in bright light.
o Affected pupil is dilated and unreactive and near reflex also absent
o Cause – enlarging aneurysm on the posterior communicating artery, can also be trauma, tumour and other space occupying lesion.
If associated pain refer immediately
o Without Pupil Involvement – generally vascular in origin related to diabetes or hypertension
o In cases of recovery – upper lid elevates as px looks down due to aberrant regeneration

Question 20

Describe Argyll-Robertson pupil (parasympathetic problem)?

Answer 20

Damage to the parasympathetic pathway
It arises from an interruption of fibres from the Edinger-Westphal nuclei that connect the pretectal nuclei
Both pupils affected but Anisocoria present due to asymmetrical involvement
Aetiology:
* Neurosyphilis (lesion around the Edinger-Westphal nucleus)
-> Neurosyphilis is presumed until proven otherwise
* Long term diabetes
* Alcoholism
Signs:
* Pupils are both small (v miotic)
* Respond poorly or not at all to light
* Normal response to near (light-near dissociation)
* Pupils irregular in shape

Question 21

What does damage to the sympathetic branch of the efferent pathway cause?

Answer 21

Damage to the sympathetic branch causes a miotic pupil, as it affects the dilator muscle
-> Aka. Horner’s Syndrome
o Can have life-threatening aetiology!!!

Question 22

Describe Horner’s syndrome (sympathetic problem)?

Answer 22

Pupillodilator dysfunction
Caused by damage to the sympathetic pathway
Due to the denervation of the sympathetic supply (disrupted pathway)
Common Aetiology:
* Lung Cancer
* Pancoast Tumour
* Carotid aneurysm
* Lesion in the neck (malignant cervical lymph nodes)
* Idiopathic
Signs:
* Unilateral
* Mild ipsilateral ptosis
* Lower lid elevation
* Miosis (due to unopposed constriction of
sphincter pupillae)
* Dilation lag of affected pupil
* Facial anhidrosis (swear gland denervation)
* Iris heterochromia (in those with congenital Horner’s)
* Pupil reacts NORMALLY to light & near