Eyelid and pupil disorders Flashcards
What causes constriction of the pupil
- Circular muscles in the iris 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 causes dilatation of the pupil
- dilator muscles of the pupil arranged like spokes on a bicycle wheel travelling straight from the inside to the outside of the iris.
- stimulated by the sympathetic nervous system using adrenalin as a neurotransmitter.
What can lead to abnormal pupil shape
- Trauma to the sphincter muscles in the iris (surgery)
- Anterior uveitis can cause adhesions (scar tissue) in the iris that make the pupils misshapen.
- Acute angle closure glaucoma
- Rubeosis iridis (neovascularisation in the iris)
- Coloboma
- Tadpole pupil
What is Rubeosis iridis
(neovascularisation in the iris) can distort the shape of the iris and pupil. This is usually associated with poorly controlled diabetes and diabetic retinopathy.
What is Coloboma
congenital malformation in the eye. This can cause a hole in the iris causing an irregular pupil shape.
How can acute angle closure glaucome cause a mishapen pupil
can cause ischaemic damage to the muscles of the iris causing an abnormal pupil shape, usually a vertical oval.
What is tadpole pupil
there is spasm in a segment of the iris causing a misshapen pupil. This is usually temporary and associated with migraines.
Causes of Mydriasis (Dilated Pupil)
Third nerve palsy Holmes-Adie syndrome Raised intracranial pressure Congenital Trauma Stimulants such as cocaine Anticholinergics
Causes of Miosis (Constricted Pupil)
Horners syndrome Cluster headaches Argyll-Robertson pupil (in neurosyphilis) Opiates Nicotine Pilocarpine
What is the presentation 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.
Which extraoccular muscles are NOT supplied by the occulomotor nerve
lateral rectus and superior oblique
Causes of a full third nerve palsy
Idiopathic Tumour Trauma Cavernous sinus thrombosis Posterior communicating artery aneurysm Raised intracranial pressure
What is the pathophysiology behind a full third nerve palsy
compression of the nerve, including the parasympathetic fibres. This is called a “surgical third” due to the physical compression:
Why may a third nerve palsy spare the pupil
suggests a microvascular cause as the parasympathetic fibres are spared. This may be due to:
- Diabetes
- Hypertension
- Ischaemia
What is the triad of Horner’s syndrome
Ptosis Miosis Anhidrosis (loss of sweating) (enopthalmos) ( Light and accommodation reflex not affected)
What is enopthalmos
sunken eye
What causes horners syndrome
- Damage to the sympathetic nervous supply to the face
- Damage can be in the pregnanglionic nerve, in the central nervous system or in the post ganglionic nerve
How can we tell where the lesion is causing Horner’s syndrome
- Central lesions cause anhidrosis of the arm and trunk as well as the face.
- Pre-ganglionic lesions cause anhidrosis of the face.
- Post-ganglionic lesions do not cause anhidrosis.
What causes the central lesions in Horner’s SYndrome
S – Stroke
S – Multiple Sclerosis
S – Swelling (tumours)
S – Syringomyelia (cyst in the spinal cord)
What causes the Pre-ganglionic lesions in Horner’s Syndrome
T – Tumour (Pancoast’s tumour)
T – Trauma
T – Thyroidectomy
T – Top rib (a cervical rib growing above the first rib above the clavicle)
What causes the Post-ganglionic lesion in Horner’s syndrome
C – Carotid aneurysm
C – Carotid artery dissection
C – Cavernous sinus thrombosis
C – Cluster headache
How can you test for Horner’s Syndrome
- cocaine eye drops: No reaction to pupil in Horner’s syndrome
- low concentration adrenalin eye drop: Won’t dilate a normal eye but will dilate a Horner’s eye
What is Holmes Adie Pupil
- unilateral dilated pupil that is sluggish to react to light with slow dilation of the pupil following constriction due to damage to the post-ganglionic parasympathetic fibres
- exact cause unknown, possibly viral
What is Holmes Adie Syndrome
Holmes Adie pupil with absent ankle and knee reflexes.
