Week 1.06 Pupils Flashcards
What muscles do you have in the pupil and what do they do
Concentric muscles (sphincter) cause pupil CONSTRICTION
Radial muscles (dilator) cause pupil DILATION
What is the iris sphincter muscle innervated by
Parasympathetic division
What is the radial muscles innervated by
Sympathetic division
What is the neurotransmitter, receptor, location and effect of stimulation of the parasympathetic branch
Acetylcholine
Muscarinic
Sphincter muscle
Miosis
What is the neurotransmitter, receptor, location and effect of stimulation of the sympathetic branch
Noradrenaline
Alpha 1 & 2 adrenal receptors
Dilator muscle
Mydriasis
What are the two main neural pathways
Afferent neural pathway = from eye to brain
Efferent neural pathway = from brain to eye
What to look out for when doing pupil assessment
- non round pupils
- Differential pupil sizes (anisocoria)
- differential responses to light
- differential coloured irides (heterochromia)
What are the causes of non -round pupils
- trauma - blunt or penetrating
- post operative cataract
- iris clip or anterior chamber intra -ocular lens implants
- sectorial dilation - some types of drops applied to certain region
Polycoria
- presence of multiple pupils in the same eye
- may be congenital, genetic disease or trauma
- peripheral iridectomy - done to allow aqueous humour
Anisocoria: physiological or pathological?
Need to determine if present in both bright and in dim illuminations.
Physiological – difference in size between right and left (in both dim and bright) remains constant
Pathological – difference is more pronounced in with bright or dim light then could mean there is problem with neurological pathway supplying to iris.
Before dynamic tests (direct and consul) what should you check
Pupil size
Position
Iris colour
Swinging flashlight tests test which pathway
Afferent pathway - eye to brain
Swinging flashlight test
room lights half
- position light 10cm from eyes below lone of sight roughly on the midline
- illuminate re 2 seconds
- quickly swing pen torch to illuminate LE 2 seconds
- swing back to RE and repeat
- look for change in pupil size as light is moved between eyes
In a patient with RAPD (relative afferent pupillary defect) there eye will dilate when the pen torch lands on that eye. This is because signals leaving that eye aren’t getting through. Only the opposite eyes signals get through telling the eye to dilate.
What does it mean by RAPD and how to quantify
Means there’s is a lesion in the Afferent pathway of illuminated eye causing dilation
Quantifying the RAPD
- ND filter in front of good eye
- increase till normal swinging flashlight response achieved
Record at +ve RAPD, 0.2log
What does PERRLA stand for
Pupils equal, round, respond to light and accomodation
What conditions can lead to RAPD
- Optic neuritis – demyelinating inflammation of optic nerve
- Retro-bulbar neuritis
- Multiple sclerosis
- Optic atrophy – e.g. due to long standing untreated glaucoma that’s asymmetric (one eye more severe than the other)
- Retinal vascular disorder
What are 4 defects of the efferent pathway
- third nerve palsy
- Horner’s syndrome
- Argyll-Robertson pupil
- Adie’s tonic pupil
Third nerve palsy
Oculomotor nerve affected
Eyes appear down and out
Ptosis of upper lid - reduced input to leavator muscle
Sluggish or absent response to light
Dilated pupils
What are causes of third nerve palsy
- Aneurysm: junction of posterior communicating artery and internal carotid artery
- Head trauma
- Intracranial tumour
- Vascular disease - diabetes/hypertension
What is horners syndrome
- interruption of sympathetic pathways
- pathway responsible for dilating pupils so if disruption pupil will be miotic
- anisocoria greater in dim conditions
- ptosis
- facial anhydrosis (sweating) on affected side
- heterochromia
What are the causes of Horner’s syndrome
- stroke
- multiple sclerosis
- thyroid enlargement
- head or neck trauma
- aneurysm of carotid artery
- congenital (present at birth) - hypo-pigmentation of affected eye, paler iris
What’s the purpose of using apraclonidine
The confirm diagnosis of horners syndrome
- causes miosis in NORMAL eyes
- causes pupil DILATION in affected eye in Horners due to hypersensitivity that develops ‘enhancing’ effect on a-1 receptors
What is the sympathetic pathway
Sympathetic pathway – hypothalamus — spinal cord — superior cervical ganglion — dilator muscle
What is hydroxyamphetamine used for
Drug helpful for locating the lesion causing Horners syndrome
Useful for determining if lesion is post or pre ganglionic
If pupil DILATE: problem is PREGANGLIONIC
If pupil fails to DILATE: POSTGANGLIONIC
Causes of Argyll Robertson pupil
- Usually caused by neuro-syphyilis - which is an infection of the brain or spinal cord
- Typically, in ppl who have chronic untreated syphilis for a number of years
- Lesion site: fibres connecting pretectal nucleus and edinger- Westphal nucleus
- Site of lesion explains the light near dissociation
Aides tonic pupil
- Disrupts the nerve supply to the pupil sphincter – causes affected pupil to be larger
- Typically affects 1 eye – second eye involvement within months to years
- Light reflex is absent or slow
- Near constriction slow
- Accommodation response slow
- Typically affects young adults around 30
- Females more than males
What are the causes of aidies tonic pupil
- Damage to the nerve supply
- Parasympathetic fibres after the ciliary ganglion
- May follow viral illness – viral or bacterial infection that causes inflammation to the neurons of the ciliary ganglion
- Other tendon reflexes diminished then known as holmes-Adie’s syndrome
- Caused by damage to the dorsal root ganglia of the spinal cord.
