Examination of pupillary reflexes

Question 1

Which nerve systems cause dilation and constriction of the pupil

Answer 1

Constriction - Parasympathetic CNIII (based on sensory information from CNII detecting light)

Dilation - Sympathetic (based on fight or flight reaction)

Question 2

Name the 3 relfex/pathways of the eye and their purpose

Answer 2

• Light reflex - pupil constriction in reaction to light (autonomic)
• Sympathetic pathway - dilation of pupil in reaction to fight or flight (autonomic)
• Near reflex - focussing on things that are close leads to near triad of pupil constriction, convergence of eyes and accomodation by changing lens shape (autonomic and voluntary)

Question 3

Describe the light reflex and the pathway it takes

Answer 3

Light relfex - autonomic constriction of the pupil in reaction to light

1. Sensory information about an increase in light enters the eye and travels down the optic nn CN II
2. The nasal fibers of the optic nn cross at the optic chiasm
3. The optic nn is known as the optic tract after the optic chiasm
4. The optic tract send the sensory information the pretectal nucleus in the brain
5. Fibres are then sent to the Edinger-Westphal nuclei (EWN). These fibres cross allowing CONSENSUAL PUPILLARY REFLEX.
6. From the EWN CN III oculomotor emerges which goes to the pupil innervating the pupillary spincter mm causing CONTRACTION

UNLIKE THE NEAR REFLEX PATHWAY IT DOES INVOLVE THE PRETECTAL NUCLEAS THEREFORE THIS WILL BE AFFECTED BY PATHOLOGY IN THIS AREA AND THE NEAR RELFEX WILL NOT

Question 4

Describe the sympathetic reflex and the pathway it takes

Answer 4

Sympathetic reflex - autonomic dialtion of pupil in reaction to fight or flight response

1. The brain senses fight or flight
2. Sends information to the hypothalamus
3. Sends sympathetic fibres down the spine out at T1
4. These fibres travel through superior cervical ganglion and int carotid aa
5. They then hitch a ride with the opthalmic banch of the trigeminal CN V
6. Finally reaching the dilator pupilae mm causing dilation

Question 5

Describe the near reflex and the pathway it takes

Answer 5

The near triad is: convergence, pupil constriction and accomodation (rounding) of the lens in order to see things that are close

1. Either a voluntary action or a reflex from sensory information from the optic nn CN II reach the cortex
2. The cortex initiates the near reflex which passes through the EWN
3. CN III occulomottor travels from the EWN to the medial rectus, sphincter pupillae and ciliary body to converge the globe, constrict the pupil and round the lens, respectively

UNLIKE THE LIGHT REFLEX PATHWAY IT DOES NOT INVOLVE THE PRETECTAL NUCLEAS THEREFORE THIS WILL NOT BE AFFECTED BY PATHOLOGY IN THIS AREA

Question 6

What are the most important pathologies that can affect the pupil pathways

Answer 6

• Afferent pupil defect (APD)
• Relative afferent pupil defect (RAPD)
• CN III occulomotor palsy
• Horner’s syndrome
• Aide’s pupil
• Anatomical anisocoria

Question 7

Describe, give the findings and name the causes of an APD

Answer 7

• APD = CNII optic nn is dead
• Findings = The affected eye’s pupil will lack any direct reflex
• Causes = lesion of optic nn: optic neuritis, ischaemic optic nn disease, severe glaucoma, trauma, tumour

Question 8

Describe, give the findings and name the causes of an RAPD

Answer 8

• RAPD = partial destruction of optic nn
• Findings = on swinging light test when light is shone into the affected eye they will both dilate. This is because the brain isn’t percieving as much light through the affected nn so therefore will not dilate as much. Big eye in Bright light is Bad
• Causes = partial lesion of optic nn: optic neuritis, ischaemic optic nn disease, severe glaucoma, trauma, tumour, MS

Question 9

Describe, give the findings and name the causes of a CN III occulomotor palsy

Answer 9

• CN III palsy = descrease in function of nn
• Findings
  
  • Ptosis
  • Palsy of all extra occular mm excluding SO + LR giving an eye that is turned down and out
  • Dilated pupil
  • Unreactive to light direct or consensual
  • Won’t accomodate
  • UNDERLINED MAY NOT HAPPEN, AS PALSY CAN BE PUPIL SPARING IF MORE VASCULAR CAUSE AFFECTING MIDDLE OF NN (MEDICAL). RATHER THAN SURGICAL WHICH WILL COMPRESS OUTSIDE FIRST ERGO PUP INVOLVEMENT
• Causes: ALWAYS THINK POSTERIOR COMMUNICATING AA (circle of willis) ANEURYSM as it sits next to CN III other than that: trauma, tumour, infection

Question 10

Describe, give the findings and name the causes of Horner’s syndrome

Answer 10

• Horner’s syndrome: damage to the sympathetic innervation of the eye
• Findings:
  
  • Affected pupil is constricted
  • Ptosis
  • Loss of sweating on one side of face
  • Test with cocaine 4% affected pupil will not dilate in horners
• Causes: lesion anywhere along the sympathetic trunk (spine, neck, brain) tumour, aneurysm, trauma

Question 11

Describe, give the findings and name the causes of Adie’s pupil

Answer 11

Adie’s pupil:

• Parasymp neurological condition that destroys nn innervating sphincter pupillae

Findings:

• Affected pupil is abnormally dilated
• Delayed direct, consensual and accomodative reflexes
• Young patient
• May also have areflexia of knee and ankle

Causes

• Infection
• Trauma
• Vascular

Question 12

Describe and give the findings of physiological anisocoria

Answer 12

Physiological anisocoria: benign pupil size difference

Findings

• <1mm difference
• Both dilate and constrict the same relative to each other in dark and light