Pupil1

3 functions of pupils

- regulate light
- reduce spherical and chromatic aberrations
- increase depth of focus through the accommodation response

which pathway is involved in pupil miosis?

parasympathetic pathway

fibres involved during pupil constriction - inner circular muscles

what pathway is involved during pupil mydriasis?

oculosympathetic pathway

fibres involved - radial fibres dilate

when does miosis occur

light reflex
accommodative reflex

describe the parasympathetic pathway in normal light reflex

- - periphery - light stimulus - optic nerve- optic chiasm - light falls on retina
- afferent neurones (rgc) create signal travels→ visual pathway via chiasm
- 2/3rds along the way, some axons divert → pretectal nucleus

→ info relayed to EWS bilaterally→ Efferent pathway - oculomotor nerve - synapse in ciliary ganglion red nucleus
- pupil fibres travel with 3rd nerve to iris sphincter muscles for constriction (miosis)

describe pathway for sympathetic pathway

- originates in the posterior hypothalamus
- 1st order neuron travels down brainstem + spinal cord to level of C8-T2/ciliospinal centre of budge
- 2nd order neuron (preganglionic neuron) leave spinal cord and enter paravertebral chain and terminate in the superior cervical ganglion found at the skull base
- 3rd order neuron (postganglionic neuron) ascend with the ICA and join ophthalmic nerve in the cavernous sinus into the orbit via superior orbital fissure to the dilator iris muscle - midriatric pupil

summary of the sympathetic pathway

- originates in posterior hypothalamus -> down brainstem to C8-T2/cilliospinal centre of budge
- preganglionic neurons -> superior cervical ganglion
- post ganglionic neuron -> pupil/Muller muscle via long ciliary nerves

describe the near reflex

neurons -> visual cortex from LGB

• optic radiations

• visual cortext

• & represented in area 19 - near response
  - from area 19, cortical fibres descend via internal capsule and synapse with EWS nuclei
  - continue pathway for light reflex

  

causes of irregular pupils?

trauma
iris tumours
coloboma
posterior adhesions to the lens (synechiae)

whats aniridia?

absence of iris

what's corectopia?

displaced pupil

why would a 3rd nerve palsy cause pupil involvement?

efferent parasympathetic fibres travel in outer layers of 3rd nerve so external compression onto 3rd nerve causes pupil involvement

what occurs in holmes-adie tonic pupil?

-Lesion in the ciliary ganglion

Mostly affects women (30s-40s)

No response to direct/consensual light reflex

Accommodative response impaired

Due to denervation and supersensitivity

Possible reduction in knee jerk reflex

• WILL REACT TO

  0.125% PILOCARPINE

  or METACHOLINE

  CHLORIDE (2.5%)

is

which pathway is affected in dorsal midbrain/parinaud's syndrome

parasympathetic pathway affected

pupils don't constrict to light but normal constriction to accommodative target occurs

occurs in dorsal midbrain

light pathway knocked out but near pathway intact

convergence retraction nystagmus - eyes converge when looking into elevation

what are uniocular causes of a constricted pupil?

horner's syndrome
anterior segment inflammation

what is a binocular cause of a constricted pupil?

argyll robertson
convergence/accommodative spasm

another name for an RAPD? and where does lesion occur

relative afferent pupillary defect
marcus gunn pupil

Lesion - afferent pathway

• Retina, optic nerve or anterior visual pathway

• Diagnosed by the swinging flashlight test

• The affected pupil will dilate instead of constrict when

the light is transferred from the normal eye to the

abnormal eye.

• Direct response<consensual response

what are the grades pf RAPD

grade 1 - weak initial pupillary constriction, followed by greater redilation

g2 - no initial change of pupil followed by greater dilation

g3 - an immediate pupillary dilation

g4 - no reaction to light - amaurotic pupil

1. Functions of Pupils Under Normal Circumstances

• Regulates Light: Adjusts the amount of light entering the eye.

• Reduces Aberrations: Minimizes spherical and chromatic aberrations.

• Increases Depth of Focus: Improves the clarity of objects at different distances.

Miosis (Parasympathetic Pathway):

Purpose: Constricts pupils.

• Mechanisms:

  • Light reflex.

  • Accommodative reflex

Mydriasis (Sympathetic Pathway):

• Purpose: Dilates pupils.

• Mechanisms:

  • Oculosympathetic pathway.

4. Parasympathetic Pathway

Retinal Ganglion Cells: Afferent signals originate → Synapse in Pretectal Nucleus: Axons diverge from the optic tract to the superior colliculus. →EWS→ 3rd never pathway → red nucleus - Preganglionic fibers synapse in the ciliary ganglion → Post ganglionic →Iris Sphincter constrict the pupil

begins in retina → optic nerve→pretectual nucleus → EWS→ ciliary ganglion → sphincter pupillae

• Factors Influencing Size

• Factors Influencing Size:

  • Age, light intensity, drugs (pharmaceutical/recreational), emotions (fear, attraction).

• Techniques:

  • Observe shape, size, symmetry.

  • Test direct and consensual light reflexes.

  • Perform the swinging flashlight test.

  • Assess accommodation reflex.

Common Pupil Abnormalities

Anisocoria:

• Unequal pupil sizes.

• Physiological: Equal difference in dim and bright light (usually <0.8 mm).

• trauma

• coloboma - congenital defect of iris

• correctopia - misplaced pupil

• heterochromia - different iris colors

Mydriatic Pupil:

check light reaction in dark conditions

greater aniscoria in bright light may indicate:

• 3rd NP

  associated w potisis, strabismus ee - down & out & anisocoria

• affected muscles - IR, IO, MR, = inferior branch of 3rd nerve

common causes of 3NP

• microvascular - normal pupil - no pain

• aneurysm - pain, pupil involvement, emergency surgery

• trauma or tumor affecting brainstem, CS or orbital apex

• 3rd Nerve Palsy: EOM defects, ptosis, accommodation loss.

• Holmes-Adie Tonic Pupil: Parasympathetic pathway lesion (e.g., viral/bacterial infection).

• Dorsal Midbrain Syndrome: Light-near dissociation.

• Acute Glaucoma: High IOP, painful red eye.

• Trauma or pharmacological dilation.

Miotic Pupil:

Causes include:

• Horner’s Syndrome: Ptosis, miosis, anhidrosis.

• Argyll Robertson Pupil: Poor response to light, intact near reflex (e.g., neurosyphilis).

• Convergence Spasm: Often associated with accommodative issues

Failure to dilate…….?

Uniocular

• Horner’s syndrome

• Anterior segment inflammation

Binocular

• Argyll Robertson

• Convergence/Accommodative spasm

Dorsal Midbrain Syndrome:

• Light-near dissociation.

• bilateral night near dissociation - pupil accommodates but doesn’t react to light

• causes

  • tumor= pineal gland, MS or damage near superior collicolus, strokes, hydrocephalus, A/V malformation

• symptoms

  • convergence retraction nystagmus during upward gaze

  • difficulty elevating eyes

  • lid retraction

  • Pupillary light-near dissociation,

• Associated with lesions in the dorsal midbrain.

Horner’s Syndrome:

• Characteristics:

• Ptosis = disinnervation of muller's muscle

• miosis= sm pupil

• anhidrosis= no sweating on affected side = effect of vasiconstrictor fibers of the face

• causes

  • trauma

  • lung cancer

  • spinal issues

  • congenital defects

• Tests:

  • Cocaine Test: Dilates normal pupil but not Horner’s.

  • Paredrine Test: Differentiates lesion location (first/second vs. third-order neuron)

8. RAPD (Relative Afferent Pupillary Defect)

• Lesion in afferent pathway (e.g., retina, optic nerve).

  • damage to optic nerver or retina= pre chiasmal

• Detected by the swinging flashlight test:

  • Affected pupil dilates instead of constricting when light swings from the normal to the abnormal eye.

  • Causes: Optic neuropathy, retinal detachment, TED (optic nerve compression), dense cataract, , diabetic retinopathy- amaurotic eye- dense amblyopia

10. Rare Pupil Disorders

• Springing Pupil: Dilation during migraines.

• Tadpole Pupil: Sectoral dilation, often benign.

• Midbrain Corectopia: Eccentric/oval pupil associated with rostral midbrain disease

accommodation and convergence spasm

• overactive accommodation & MR o/a

• symptoms

  • diplopia

  • esotropia

  • blurred vision

• causes

  • hypermetropia without correct lenses

  • presbyopia leading to over accommodation

Diagnostic testing & therapeutic interventions

iridotomy/iridectomy - laser treatment for conditions like glaucoma

Testing for pupillary abnormalities

• bright light vs dim light anisocoria differentiation

• light near dissociation in specific syndromes

• drug testing for differential diagnosis - e.g. cocaine

LND

• Adie's or tonic pupil: A disorder that causes one or both pupils to be abnormally dilated 

• Parinaud syndrome: A rare condition that can include LND, convergence-retraction nystagmus, and up gaze palsy 

• Argyll-Robertson pupils: A pupil that constricts poorly to light but constricts well when viewing something nearby 

• Aberrant regeneration of the third nerve: Lesions in the ciliary ganglion or postganglionic nerve can cause LND 

• Optic neuropathy

what controls the pupil

A: The pupil is controlled by both sympathetic and parasympathetic nervous fibers.

What is spasmus nutans and when does it occur?

A: Spasmus nutans is an acquired form of nystagmus seen in children, usually within the first 2 years of life.

: The triad of spasmus nutans includes:

1) Nystagmus (involuntary eye movement),

2) Head bobbing,

3) Torticollis (twisting of the neck).

: Head bobbing and torticollis are thought to be compensatory mechanisms to improve vision by reducing the nystagmus' frequency and asymmetry.

Ocular Motor Apraxia (OMA)

1. A: OMA is a condition where there is a defect or absence of voluntary eye movement control. Children with OMA struggle to move their eyes in a specific direction, especially horizontally.

   A: To compensate, they use a head thrust to track objects, as they cannot initiate horizontal eye movements. Vertical eye movements typically remain unaffected.

Q: Describe the pupillary light reflex pathway.

A: 1) Light hits the retina, initiating signals in retinal ganglion cells.

2) Signals travel through the visual pathway.

3) Some axons diverge to the pretectal nucleus, relaying to the Edinger-Westphal nucleus (EWN)

4) EWN sends signals via the third cranial nerve, through the ciliary ganglion to the sphincter muscle of the iris, causing pupil constriction.

Oculocardiac Reflex (OCR)

OCR is triggered by stimulation of the vagus nerve due to traction on the extraocular muscles (EOMs), often seen in pediatric fractures, causing a reduction in heart rate (bradycardia)

Q: Describe the oculocardiac reflex (OCR) pathway.

A: 1) Afferent limb: Trigeminal nerve (CN V) carries signals from stretch receptors via ciliary nerves to ciliary ganglion, then to trigeminal nucleus.

2) Efferent limb: CNS processes information, communicates with vagus nerve (CN X) motor nucleus.

3) Vagal impulses travel to sinoatrial node, causing bradycardia.

 

what is the Near reflex

The near reflex (or near response) occurs when focusing on a close object.

1. Accommodation:

2. Convergence:

3. Pupillary Constriction:

The neurons carry on to the visual cortex from LGB, optic radiations = area 19 - visual cortex

• area 19 - interprets near object.

• Signals → via descending fibers → thru internal capsule.

• fibers synapse in the EW nucleus of midbrain.

• Parasympathetic fibers (via CN III and ciliary ganglion) cause:

  • Accommodation (lens thickens).

  • Pupillary constriction.

• Signals to MR muscles of both eyes = convergence.

pupil size depends on

• Age

• Hippus

• Light intensity

• Accommodation

• Drugs

• Pharmaceutical

• Recreational

• Psychosensory

• Attraction

• Fear

How do you asses pupil

• Observation

  • Shape

  • Size (look for anisocoria)

• Direct light reflex

• Consensual light reflex

• Swinging flashlight test

• Accommodative reflex

• Look for other abnormalities

  • Eyelids

  • Eye position

what are the main pupil abnormalities

• Anisocoria

• Mydriatic pupil

• Miosed pupil(s)

• Irregular pupils

• Trauma

• Iris tumours

• Coloboma

• Posterior adhesions to the lens (Synechiae)

Causes of a mydriatic pupil

Failure to constrict……..?

IIIrd N palsy

Holmes-Adie Tonic pupil

Dorsal midbrain syndrome

Acute glaucoma

Trauma

Pharmacological accident

Hutchinson pupil (coma)

IIIrd N palsy

Compressive

Aneurysm: Junction of Posterior communicating artery (PCA) and internal carotid artery

Associated with other EOM defects

Accommodation affected

Aberrant regeneration

Holmes-Adie Tonic Pupil

• Lesion in the ciliary ganglion

  • Bacterial/ viral infection

• Mostly affects women (30s-40s)

• No response to direct/consensual light reflex

• Accommodative response impaired - N reduced

  • Due to denervation and supersensitivity

• an enlarged pupil that constricts slowly in bright light:

• WILL REACT TO 0.125% PILOCARPINE

• or METACHOLINE CHLORIDE (2.5%)

• parasympathetic dysfunction - ciliary ganglion involvement

• Possible segmental iris palsies and reduced knee reflex

Horners syndrome

Characteristics: - PAREDINE - order neurone TEST & COCAINE

• PTOSIS, MIOSIS, ANHYDROSIS

• Additional characteristics

• Heterochromia (congenital cases)

• Apparent enophthalmos

• Can be associated with contralateral IVth N (nuclear/fascicular) or VIth N (cavernous sinus)

Anisocoria increses in dim light

• Cocaine (2-4%) dilates a nomal pupil but not a Horner’s !

• 1st (central), 2nd (Preganglionic) or 3rd (Post-ganglionic)order neuron lesion differential diagnosis

• Differential diagnosis test: PAREDRINE (1% Hydroxyamphetamine) drops will fully dilate the pupil if 1st or 2nd order neuron lesion, but subnormal dilation if 3rd neuron.

Second Order neuron lesion- Pancoast’s tumour

• can lead to horners

Argyll Robertson

• Usually bilateral miotic pupils

• May be asymmetrical

• Poor dilation in the dark and to mydriatics

• Light-Near dissociation

• NO response to light

• Responds to near target

• Hallmark of neurosyphilis

• Site of lesion: Region of the Sylvian aqueduct in the rostral midbrain

• no diplopia

Afferent Pupillary Defect- (Marcus Gunn Pupil)

Some of the conditions that exhibit RAPD are:

Optic Neuropathy

Extensive retinal damage (Central retinal artery/vein occlusion, marked retinal detachment)

TED – optic nerve compression

Amaurotic pupil- “Blind Eye”

Mild RAPD- amblyopia

parasympathetic pathway - constriction

Parasympathetic Pathway

• Retinal Ganglion Cells: Afferent signals originate here.

• Synapse in Pretectal Nucleus: Axons diverge from the optic tract to the superior colliculus.

• Edinger-Westphal Nucleus: Bilateral relay of information.

• Third Nerve Pathway: Preganglionic fibers synapse in the ciliary ganglion.

• Iris Sphincter Activation: Postganglionic fibers constrict the pupil.