BS - Pupil Disorders - Week 4 Flashcards
What is the difference between an afferent and efferent pathway?
Afferent - eye to CNS
Efferent - CNS to eye via ANS
What are the two types of efferent pathways to the eye?
Sympathetic
Parasympathetic
Name 4 innervational problems to the iris.
Anisocoria Abnormal: -Direct -Consensual -Near
Describe the parasympathetic pathway to the iris (4), the effect on the pupil, the neurotransmitter used, and the receptor type (2).
Begins at the Edinger-Westphal nucleus, leaving with CN3
Travels to the ciliary ganglion (CN5)
Travels via the short ciliary nerve to the sphincter pupillae
Causes constriction
Uses Ach neurotransmitter
Nicotinic receptors are used at the ciliary ganglion
Muscarinic receptors are used at the iris
Where is the ciliary ganglion found in relation to the eye?
Just behind the eye temporally
Describe the sympathetic pathway to the iris (8), the effect on the pupil, the neurotransmitter used, and the receptor type (2).
Originates from the thalamus/hypothalamus in the midbrain.
Preganglionic fibres travel to the ciliospinal centre at T1 via the long ciliary nerve.
An interneuron relays to the superior cervical ganglion from T1.
Postganglionic fibres start at the superior cervical ganglion and follow the carotid plexus, through the cavernous sinus, to the dilator pupillae muscle.
It dilates the iris.
Uses Ach neurotransmitter.
Nicotinic receptors are used at the superior cervical ganglion
Adrenergic receptors are used at the iris
Consider an eye with RAPD/Marcus Gunn pupil. List 7 pathologies that would indicate the problem is before the chiasm.
Large retinal detachment Central retinal artery occlusion Central retinal vein occlusion Optic nerve ischaemia Asymmetric glaucoma Optic neuritis Optic nerve compression
Which of the following do not cause RAPD?
Cataracts
Vitreous haemorrhage
Amblyopia
All of them
Note - amblyopia may present a mild RAPD
True or false
Anisocoria is a feature of RAPD
False, it is not a feature
Pupil sizes are equal in light and dark
Describe how both pupils react in a swinging flashlight test in someone with RAPD.
Normal eye - regular small relaxation after initial constriction
Affected eye - both pupils dilate
Describe video pupillometry.
An infrared camera is used to automate pupil size measurement.
How do the following conditions affect constriction and relative escape?
Brighter
Dimmer
Diseased eye
Brighter - more constriction, less relative escape
Dimmer - less constriction, more relative escape
Diseased eye - less light delivered=less constriction, more relative escape
What is meant by relative escape in pupillometry?
Consider a normal pupil response vs a diseased eye pupil response.
The difference between the two recovery phases after constriction is the relative escape.
Differentiate between a mild and severe RAPD pupillometry response.
After shining light into the good eye, it will drive a consensual response in the affected eye.
Mild - affected eye has some constriction will occur, but less than the good eye, and will have an early escape (quicker dilation).
Severe - affected eye has no constriction
What three sites are suspected of injury if there is an RAPD?
Gross retinal pathology
Optic nerve pathology
Pre-brainstem optic tract pathology
Describe the 5 grades of RAPD.
No RAPD (0) - pupils constrict and show equal physiological escape
+1 - affected eye escape after 3 seconds only
+2 - affected eye escape after 2 seconds only
+3 - affected eye escape after 1 seconds only
+4 - immediate affected eye escape
True or false
An efferent pathway dysfunction never causes anisocoria
False, it does
True or false
An afferent defect NEVER causes anisocoria
True
Consider the sympathetic efferent pathway. How many interneurons does it have, where are they located, and what 4 structures do they supply?
3 interneurons, 2 CNS, 1 periphery Supplies: -Pupil dilator (dark) -Muller muscle (lids) Facial sweat glands Ocular blood vessels
Which dermatome is the Edinger-Westphal nucleus found? What about the ciliary ganglion?
EWN - C
What 2 things does the parasympathetic efferent pathway supply, and what three reflexes does it produce?
Sphincter pupillae
Vergence/accommodative input
Produces the D, C, N reflexes
True or false
Innervation problems ALWAYS give abnormal pupil reflexes
True
The following indicate a problem with which pathway?
Greater anisocoria in the dark
Greater anisocoria in the light
Name which pupil and muscle would be the defective one.
Light - parasympathetic problem, sphincter pupillae doesnt constrict, defective pupil is the larger one
Dark - sympathetic problem, dilator action is weak, defective pupil is the smaller one
Describe what is meant by dilation lag, and what it is a characteristic sign of?
The anisocoria is most evident during the first 4-5 seconds of being in dim conditions. The affected eye (smaller one) will slowly dilate or ‘lag’ over 10-15 seconds, making the anisocoria less evident.
It is characteristic of Horner’s syndrome
If dilation lag is observed, what 6 other pathologies should be looked for, and what condition do they indicate?
Ptosis Facial anhydrosis IOP reduced on the affected side Conjunctival flush Increased accommodation (1.00D) Iris heterochromia (congenital/very long standing) They are indicative of Horner's syndrome
Suppose dilation lag and iris heterochromia is seen, what condition does this indicate, and why does it present with iris heterochromia?
What two additional pathologies are seen with this condition?
Congenital Horner's syndrome This is due to sympathetic innervation being needed to develop iris pigmentation Additionally causes: Brachial plexus trauma Forceps delivery at birth
Consider a parasympathetic dysfunction. How can a mid-brain lesion be differentiated from a peripheral lesion (4)?
Mid-brain lesion will result in the following:
No light reflex to light
Near reflex observed
Peripheral lesion will result in the following:
No light or near reflex
Name 2 conditions that can cause a mid-brain lesion.
Syphilis
Parinauds (aqueductal stenosis)
Name 4 conditions that can cause a peripheral lesion.
Iris trauma (increased IOP)
CN3
Drug usage
Viral (Adies: HZV)
Consider an individual with Parinaud’s syndrome. What pathway defect do they have, where is the lesion, and describe what it can be caused by, and any eye conditions they might have aside from a defective pupil.
Parasympathetic pathway defect
Mid-brain lesion (posterior)
Can be due to pineal tumour
Have nystagmus on attempted gaze
Consider an individual with an Argyll Robertson pupil. What pathway defect do they have, where is the lesion, and describe what it can be caused by, and any eye conditions they might have, including their reaction to light.
Parasympathetic pathway defect
Mid-brain lesion, supra-nuclear Edinger-Westphal lesion in the descending pathways
Pupils are irregular and miotic
Total absence of light response
Brisk near response
Affects both sides of the EW to give a smaller pupil
Can be caused by syphilis
Describe a light and near dysfunction, what conditions it is most apparent in, and its most common cause. Describe why a lack of near response is a good thing (2), and what response is often seen.
Poorly responsive, large pupil to light and near. Most apparent in bright light. Adies is the most common cause. Lack of near is good because it means: -peripheral cause -no light near dissociation Often a tonic response.
Consider a peripheral ANS lesion. What effect does this have?
Muscle on the involved side becomes suprasensitive to agonists (Adrenaline/Ach)
Consider a sympathetic ANS lesion. What two drugs would be used to determine this?
Phenylephrine 2.5%
Aprachlonidine 0.5%
Consider a parasympathetic ANS lesion. What drug would be used to determine this?
Pilocarpine 1%
What effect does low dose pilocarpine have on a normal pupil vs an Adies pupil, and what does this suggest?
Little effect in normal eyes, but a marked effect in Adies pupils, suggesting parasympathetic dysfunction.
