Unit 2 - Pupil Defects Flashcards
What does the sympathetic pathway control?
Dilator muscle
What muscle does the parasympathetic pathway innervate?
Sphincter muscle
What pathway does the sympathetic pathway take?
First order neuron: hypothalamus to ciliary centre of bulge
Second order neuron: enters sympathetic chain at level of stellate ganglion, synapse at superior cervical ganglion
Third order neuron: Fibres to eye run along the ICA as it enters cavernous sinus, most run along ophthalmic division of trigeminal nerve to innervate dilator pupillae and Muller’s muscle
What pathway does the efferent branch of the parasympathometic nervous system follow?
Starts at Edinger-Westphal nucleus
Follows third nerve, following inferior division at cavernous sinus
Synapses at ciliary ganglion
Goes on to innervate the sphincter and anterior segment
What is the afferent pathway of the parasympathometic system?
Follows optic nerve
Synapses at pretectal synapse in occipital lobe
Goes on to Edinger-Westphal nucleus
What percentage of patients have anisocoria?
20%
How can you differentiate between physiological and pathological anisocoria?
Pathological becomes more pronounced in either dim or bright light whilst physiological stays the same.
How much of a difference in pupils is required for it to be termed anisocoria?
0.4mm
What causes a RAPD/Marcus Gunn pupil?
Severe damage to retina, optics nerve, chiasm, optic tract or mid-brain pre-tectal area.
What are the signs of Horner’s syndrome?
Miosis
Ptosis
Facial anhydrosis (only if lesion is close to superior cervical ganglion)
Dilation lag in the affected pupil
Heterchromia may be present in congenital form.
What tests are used to diagnose a Horner’s syndrome?
Apraclonidine (alpha 2 agonist and weak alpa 1 agonist) will reverse miosis. (Need to wait a full 40 mins and you need a full reversal for the test to be considered positive.
Cocaine: prevent reuptake of noradernaline at pre-synaptic neuron thus exacerbating antisocoria. It would dilate it in a normal pupil
Compression of 3rd cranial nerve will compress with pupillary nerve fibres?
Efferent
What ocular signs would you get with a 3rd nerve palsy?
- Ptosis
- Diplopia due to vertical and exo deviation on affected side
- Mydriasis of affected eye
Will a third nerve anisocoria increase or decrease in bright light?
Increase as normal pupil mioses normally
What is a common cause for a 3rd nerve palsy?
Enlarging aneurysm of the posterior communicating artery.
What path of the pathway is affected in Adie’s tonic pupil?
Parasympathetic denervation at the level of the ciliary ganglion
What are the signs of Adie’s tonic pupil?
- Affected pupil larger with segmental paralysis leading to abnormal shape
- Light reaction is slow
- Near reaction is present but slow
- Loss of sweating, tendon reflexes and accommodation
- Corneal anaesthesia may be present
What does corneal anaesthesia confirm in Adie’s tonic pupil?
that ciliary ganglion is the site of the lesion.
What are the causes of Adie’s tonic pupil?
May be idiopathic or due to an unknown viral cause. E.g. varicella?
What test can be done to confirm Adie’s tonic pupil?
- Pilocarpine 0.125%, a genuine Adie’s is super sensitive and there will be a marked miosis.
- Unaffected eye won’t constrict. BUT an absent super sensitivity does not rule out Adie’s especially if it is acute and regeneration of nerves has not occurred.
What is the prognosis with Adie’s pupil?
Accommodation will often improve with time
What is a cause of unilateral mydriasis often associated with headache
Benign episodic unilateral mydriasis.
What are the symptoms of benign episodic unilateral mydriasis
Isolated unilateral mydriasis. Pupils are not tonic and light responses are normal.
Attack can last 12 hours but can be 10mins to 1 week.
May be associated with headaches, visual blue and orbital discomfort.
When should phenylephrine (alpha -1 agonist) be used with caution?
Alpha 1 receptors are found in blood vessel walls, heart muscle and the neck of the bladder.
- Coronary artery disease - can reduce cardiac output and slow heart rate
- Heart disease
- Artherosclerosis - can cause chest pain
- Overactive thyroid - more likely to get cardiac side-effects
- Diabetes - long standing insulin dependent more likely to get high BP
- High BP
- Enlarged prostate - can cause urine retention
What does tropicamide do?
Restricts action of sphincter causing dilation.
What does 2.5% phenylephrine do?
Stimulates dilator muscle
In a congenital Horner’s syndrome which eye will be lighter and why?
Affected eye is lighter. Melanin production is thought to be under sympathetic control.
Why does apraclonidine test work with Horner’s?
Denervation in Horner syndrome results a-1 receptors in the iris becoming supersensitive. This causes mydriasis but will have with little or no effect on normally innervated eyes.
Why does cocaine test work with Horner’s?
It block re-uptake of noradrenaline. In a normal pupil this will cause dilation but in a Horner’s pupil less noradrenaline is produced so there will be minimal change and anisocoria will be exacerbated.
What do we need to be aware of if a child presents with horner’s?
Neuroblastoma, 2% present with Horner’s
What causes are there of Horner’s in adults?
1st neuron: Stroke, tumour, cervical spondylitis, neck trauma
2nd neuron: apical lung tumour, cardiothoracic surgery
3rd neuron: carotid dissection or aneurysm, cavernous sinus tumour
