Pupil Assessment

What is the pupil?

• An opening in the centre of the iris

• controlled by sphincter + dilator muscles

Which muscle causes pupil constriction?

• iris sphincter contracts causing constriction → miosis

• closest to pupil

Which muscle causes pupil dilation?

• The radial dilator muscle contracts causing dilation→ mydriasis

What is the Relationship between sphincter and dilator muscles

• They are antagonistic muscles working in opposition

What are the Three main pupillary reflexes?

1) Light/dark reflex

2) near reflex

3) and psychosensory reflex

What is the Light/dark reflex?

• pupils constrict in response to bright light

• pupils dilate in dark

What is the Near reflex?

• Accommodation and convergence are linked with pupil constriction

(Near Triad)

What is the Psychosensory reflex?

• can override light reflex + relates to emotional state

• Pleasant emotions = pupil dilation (arousal,fear shock etc → fight or flight)

• Unpleasant emotions = pupil constriction (anger, boredom)

What are the Functions of the pupil?

• Controls depth of focus→ pupil constriction gives greater depth of focus

• Signalling → pleasant emotional states or shocking stimuli → pupil dilation

• controls how much light enters eye → protective effect e.g reducing UV

• aids night vision by minimising amount of light adaptation that occurs → speeds up dark adaptation

• minimising aberrations from peripheral cornea/lens

What is the Stiles–Crawford effect?

• light appears brightest when entering centre of pupil

• as cones in retina been directed towards centre of pupil

• lower photoreceptor response from orthogonal rays

• so large pupils dont limit our acuity vastly

Why large pupils do not greatly reduce acuity

Peripheral rays stimulate cones less effectively.

Parasympathetic innervation controls

• iris sphincter controlled by parasympathetic nerves

• responsible for constriciton

Sympathetic innervation controls

• Pupil dilation via the dilator muscle

What is the Afferent pathway of pupillary light reflex

light enters + stimulates Retina → optic nerve → optic chiasm

fibres from nasal retina cross to opposite (contralateral side ) temporal fibres stay on same (ipsilateral )side

→ fibres project to pretectal nuclei in midbrain

→ pretectal nuclei project fibres to both ipsilateral + contralateral Edinger Westphal Nuclei

Crossing at optic chiasm (pupil reflex)

Nasal retinal fibres cross; temporal fibres remain ipsilateral.

Role of pretectal nuclei

Project to both Edinger–Westphal nuclei.

What is the Efferent pathway of light reflex (Parasympathetic Pathway)

Edinger–Westphal nucleus → CN III → ciliary ganglion → short ciliary nerves → sphincter

What is the Consensual response?

• fibres from both eyes synapse onto both pretectal nuclei which innervate both Edinger Westphal nuclei

• Light in one eye causes EQUAL constriction of both pupils

What is the Pupillary Dark reflex mechanism

• pupils dilate in response to darkness

• results from contraction of radial dilator muscle of iris + under control of sympathetic pathway

• afferent pathway can be described as retina signalling an absence of light to hypothalamus in brain

What is the Sympathetic pathway → efferent pathway

• originates in hypothalamus in brain → spinal cord → chest cavity → alongside carotid artery → enters eye via LONG ciliary nerves

What are the effects of problems that arise from the sympathetic pathway ?

• Results in a miotic pupil because parasympathetic nerves which control constriction are unopposed

• diseases arising in spinal cord, chest + neck → lung cancer + aneurysm can sometimes manifest with ocular sign

—> Horner’s syndrome

What does the Near response involve?

> Triad :

• Pupillary constriction

• Accommodation

• Convergence

> response is automatic when an out of focus near object viewed

> stimulus = blurred retinal image + equal in both eyes

> occurs to maximise resolution acuity rather than to allow greater lag of accommodation

What is the normal adult pupil size range

Approximately 2–8 mm → varies with age + room illumination

Key features to assess on inspection of the pupil

• Shape → should be round

• Equality → do both pupils look equal

What is the Direct pupillary response (pen torch)

• does pupil constrict when light shone directly into eye

What is the Consensual pupillary response (pen torch)

• Constriction of the fellow eye when light shone onto other eye

What is the Near response assessment?

• Pupils constrict when moving from distance to near target

What is the Relative afferent pupillary defect (RAPD)?

• swinging flashlight test → alternate between both eyes

• is there a relative difference in pupil cosntrcition

What is Heterochromia?

• difference in colour of two irides

• usually congenital

• if acquired associated with:

• Cataract

• Glaucoma

• Iridocylitis → type of uveitis

• Iris melanoma (cancer)

What is a RAPD?

• Relative Afferent Pupillary Defect

• tests for problems in afferent pathway → is there a asymmetrical defect in optic nerve or retina

• affected eye will DILATE when light shone onto it as signals cant reach brain

• under normal lighting conditions both pupils appear equal → consensual reponse

• AKA Marcuss-Gunn Pupil

• causes: Advanced glaucoma, retinal detachment , central retinal artery occlusion

How pupil reactions are recorded

• Tick box grid → direct, consensual + near

• Number scale → 0-4 where 0 is no relation and 4 is brisk normal reaction

• PERRLA → Pupils equally round & Reactive to Light and Accommodation

• generally write ‘no RAPD’ and ‘no Aniscocoria’ next to all of above if appropriate

What Is Physiological anisocoria?

• one pupil naturally slightly larger than the other

What are the Key features of physiological anisocoria?

• Size difference <1 mm + consistent in all lighting

• present in ~15-20% of pop

• present at birth

• no visual side effects

Pupil appearance in Horner’s syndrome

• Miotic → more noticeable in dim light

Pathway affected in Horner’s syndrome

Sympathetic pathway.

Other signs of Horner’s syndrome

• Ptosis with normal light response

Why Horner’s syndrome is concerning

May indicate life threatening conditions such as stroke or lung tumour, spinal cord tumour

can be checked at hospital through instillation of a drop that block sympathetic pathway → 10% cocaine

• causes pupils to dilate in physiological aniscocoria

• but NO DILATION of affected eye in Horner;s syndrome

Adie’s pupil appearance

• Dilated pupil and slow to react in reponse to light

Key feature of Adie’s pupil

• Light–near dissociation → responds normally to near objects but slow to re-dilate at distance

• rare neurological disorder → idiopathic

• may indicate selective degeneration of nerves supplying parasympathetic pupil pathway → ciliary ganglion

• non-progresive + unilateral

• may also be called Tonic Pupil or Holmes-adie pupil

• may complain of light sensitivity

Typical demographic for Adie’s pupil

• More common in females + avg age of onset around 30 years

• No Tx required

Long-term change in Adie’s pupil

May become miotic over time ('little old Adie')

What are the Signs of third nerve palsy?

• Ptosis

• dilated pupil

• eye positioned 'down and out'

• Px likely to complain of diploma if acquired

Common causes of third nerve palsy

• Ischaemia

• aneurysm

• tumour

What is an Iris coloboma?

• Congenital abormaility where iris doesn’t form properly

• can also affect retina + optic nerve

What is Persistent pupillary membrane?

• Remnants of membrane that supplied blood to lens during development

Iris trauma after cataract surgery

• clips used to hold pupil open

• May result in irregular pupil shape