Pupils

Physiology

• Iris has two muscles:

o Pupil dilator

- Constriction of this muscle results in pupil dilation (mydriasis)

- Peripherally located

o Sphinctor

- Located more centrally and around edge of pupil

- Constriction causes pupil constriction (meiosis)

• Intrinsically photosensitive retinal ganglion cells (ipRGCs)

o Contain melanopsin

o Only a small number of neurons compared to standard photoreceptors

o Not affected in diseases that affect retinal photorecptors or disease that affect RGC (e.g. LHON

- Thus pupil function remains normal despite severe visual loss

o There is asymmetry of two working hemifields regarding ipRGCs

- Nasal hemifield gives a stronger response than temporal hemifield

- Thus an RAPD can occur with optic tract lesion

• ipRGCs project to pre-tectal nucleus in the midbrain

• Interneurons synapse from PTN bilaterally to Edinger-westphal nucleus (although mainly contralateral

• Parasympathetic fibres travel from EW nucleus to join 3^rd nerve

o Run along outer fibres of 3^rd nerve.

o 3^rd nerve divided into 2 divisions in anterior cavernous sinus – PS fibres follow inferior division into the orbit

o PS fibres synapse in ciliary ganglion

o Cilliary ganglion lies in posterior orbit between lateral rectus and optic nerve

o Post-ganglionic fibres join short ciliary nerves

o Nerves travel to inferior oblique then into the globe between sclera and choroid

o Innervate ciliary muscle and sphincter muscle

o Number of fibres ciliary body:sphincter 30:1

• Near response

o Triad:

- Meiosis

- Accommodation

- Convergence

o Rostral superior colliculus appears to be where this response is coordinated

o Final pathway for Meiosis and accommodation however is still via EW nucleus

Pupillary dilation

• First order – hypothalamus to spinal cord (C8-T2)

• Second order – exits spinal cord, over the surface of the lung, up along the carotid artery

o Synapses in superior cervical ganglion

• Third order

o Follows carotid up to and through cavernous sinus

o Follows 6^th nerve

o Then 5^th (nasocilliary branch)

o Then long ciliary branch into the orbit

o Synapses on dilator muscle

o Adrenergic – causing contraction of muscle and pupil dilation.

Examination

• Size

• Equal/anisocoria

o Light

o Dark

• Dilation in dark

• Reactive to light

• RAPD

• Constriction at near

• Examine condition of iris –

o Irregular edge suggesting trauma

o

Testing

Cocaine

• Blocks NA reuptake

• Requires intact sympathetic fibres

• Will have no effect if sympathetic fibres not present or functioning

Apraclonidine

• Direct alpha receptor agonist

• No effect on eyes with intact sympathetic innervation

• Mild pupillary dilation in eyes with sympathetic denervation – regardless of lesion location

• Reverses the Horner syndrome – confirms diagnosis

Hydroxyamphetamine

• Releases stored NA form the postganglionic adrenergic nerve endings

• Causes pupillary dilation in eyes with intact sympathetic innervation

• Has no effect on third order Horner’s

Imaging

First order

- CXR

- CT Chest

- MRI head and neck

- MRA/CTA

Third order

MRI brain

• )

Bilateral poorly reactive pupils

• Dorsal midbrain lesion

o With upgaze palsy

• Miller fisher

• Botulism

• DM

•

Small pupil abnormal (failure to dilate)

Causes:

• Iris abnormality

• Horner’s

• Physiological

• Pharmacological

Large pupil abnormal (failure to constrict)

Causes

• Third nerve palsy

• Tonic pupil

• Pharmacological

o Iatrogenic – e.g ipratropium

o Plants

• Damaged iris sphincter

o Glaucoma

o Iritis

Third nerve palsy

See

N.B. It is very rare to see an isolated anisocoria in a 3^rd nerve palsy (in an alert patient)

Tonic Pupil

Pathophysiology

• Damage to the ciliary ganglion or short ciliary nerves

• Partial preservation of the parasympathetic fibres results in sectoral paralysis

• Light -near dissociation - ?due to larger percentage of fibres to accommodation

Causes:

• Adie (or Holmes Adie) syndrome

o Tonic pupils

o Loss of deep tendon reflexes

o If combined with segmental anhidrosis = Ross syndrome

• Local ocular processes affecting ciliary ganglion

o Orbital trauma, sarcoid, viral, GCA, strabismus surgery, orbital tumours, laser photocoagulation

• Autonomic dysfunction

o Long list of associated autonomic conditions – including syphilis, severe DM, amyloid…

• Idiopathic

Presentation

• Asymptomatic anisocoria

• Painless

• May be difficulty reading

• Difficulty refocusing from near to far

• Photophobia

Examination

• Anisocoria – worse in the light

o N.B. after 1-2 months a tonic pupil may become miotic and smaller than fellow pupil

• Light-near dissociation

o Occurs 8 weeks after denervation, due to abberant reinnervation by accommodative fibres onto iris

• Tonic redilation

• Sectorial paralysis

• Vermiform movements of the iris

• Loss of pupillary ruff

• Depressed corneal sensation

• Bilateral in 10%

Testing

Dilute pilocarpine test

Pilocarpine is a mACh R agonist

Testing

RPR, ANA, ACE, ESR, BSL