Examination of the pupils and optometry Flashcards
(46 cards)
What causes pupil constriction?
There are circular muscles in the iris that cause pupil constriction. They are stimulated by the parasympathetic nervous system using acetylcholine as a neurotransmitter. The fibres of the parasympathetic system innervating the eye travel along the oculomotor (third cranial) nerve.
What muscles cause pupil dilatation?
The dilator muscles of the pupil
They are arranged like spokes on a bicycle wheel travelling straight from the inside to the outside of the iris. They are stimulated by the sympathetic nervous system using adrenalin as a neurotransmitter.
What is the consensual reflex?
What causes it to occur?
Shining of light in one eye causes both eyes to constrict
post-ganglionic parasympathetic neurone passes to sphincter papillae, which is distributed with ophthalmic division of the trigeminal nerve.
The bilateral distribution in the brainstem = constriction of both pupils
What is the Edinger-westphal nucleus?
Parasympathetic nucleus of the oculomotor nerve (CNIII)
Describe the parasympathetic pathway
Originates in Edinger-Westphal sub-nucleus of CNIII
Passes with CNIII to synapse in ciliary ganglion before supplying constrictor papillae of the iris
Why is the sympathetic pathway relevant to the eye?
Causes of HORNER’S SYNDROME
Describe the pathway of the sympathetic pathway
(relevant for the causes of Horner syndrome)
The sympathetic nerves arise from the spinal cord in the chest. These are pre-ganglionic nerves.
They then enter into the sympathetic ganglion at the base of the neck and exit as post-ganglionic nerves. These post-ganglionic nerves then travel to the head, running alongside the internal carotid artery.
How do sympathetic pathway fibres get distributed to the eyeball?
- passing through ciliary ganglion without synapsing; joining the short ciliary nerves, which pass along the long ciliary nerve to reach the eye ball
- passing along the ciliary nerve to reach the eye ball
What is the accommodation response?
Enables us to look at and focus upon objects close to the eye
How can you detect RAPD
swinging light test
patient’s pupil constricts less when the light is moved from unaffected eye to affected eye
What are the causes of RAPD?
Optic nerve ischaemia, optic neuritis, compression, asymmetric glaucoma
Central retinal artery or ischaemic central retinal vein occlusion
Large retinal detachment
What is the presentation of Horner’s syndrome?
Ptosis
Miosis
Anhydrosis
Enophthalmos (sunken eye)
What is the cause of Horner’s syndrome?
Central lesions (4 Ss):
S – Stroke
S – Multiple Sclerosis
S – Swelling (tumours)
S – Syringomyelia (cyst in the spinal cord)
Pre-ganglionic lesions (4 Ts):
T – Tumour (Pancoast’s tumour)
T – Trauma
T – Thyroidectomy
T – Top rib (a cervical rib growing above the first rib above the clavicle)
Post-ganglionic lesion (4 Cs):
C – Carotid aneurysm
C – Carotid artery dissection
C – Cavernous sinus thrombosis
C – Cluster headache
How is Horner’s syndrome tested for?
4% cocaine test - Horner’s pupil will not dilate
Apraclonidine 0.5% - Horner’s pupil will dilate
What is the appearance of a third nerve palsy?
Ptosis (drooping upper eyelid)
Dilated non-reactive pupil
Divergent strabismus (squint) in the affected eye. It causes a “down and out” position of the eye.
What are the causes of third nerve palsy?
A third nerve palsy with sparing of the pupil suggests a microvascular cause as the parasympathetic fibres are spared. This may be due to:
Diabetes
Hypertension
Ischaemia
A full third nerve palsy is caused by compression of the nerve, including the parasympathetic fibres. This is called a “surgical third” due to the physical compression:
Idiopathic Tumour Trauma Cavernous sinus thrombosis Posterior communicating artery aneurysm Raised intracranial pressure
What is an Adie’s pupil?
unilateral dilated pupil that is sluggish to react to light with slow dilation of the pupil following constriction. Over time the pupil will get smaller. This is caused by damage to the post-ganglionic parasympathetic fibres. The exact cause is unknown but may be viral.
Holmes Adie Syndrome is where there is a Holmes Adie pupil with absent ankle and knee reflexes.
What is the cause of Adie’s pupil?
damage to the post-ganglionic parasympathetic fibres - may be associated with reduced tendon reflexes
What can you do to determine diagnosis of Adie’s pupil?
Use pilocarpine to determine diagnosis by constricted affected pupil
What is an Argyll-Robertson pupil?
bilateral small pupils reduce in size on near object, do not constrict when exposed to bright light 'accomodate, but do not react' (prostitute's pupils) Finding of neurosyphilis
What is the cause of Argyll-Robertson pupils?
neurosyphilis
What is the cause of traumatic mydriasis?
Blunt trauma
What Is posterior synechiae?
Adhesion of the iris pigment epithelium to the lens - causes an irregularly shape fixed pupil
What is vision?
The level of detail an eye can see without any aid
