W17 - pupil pathologies

what is isocoria

when both pupils are equal in sizw

pupil size in healthy eye

2-4 mm in bright light

4-8 mm in darkness

why does pupil size change in dark and light

to modulate retinal illumination

optimise optics - balance competing demands for diffraction (high for small apertures) and optical aberrations (high for large apertures)

increase depth of field

what is the accommodative triad

refractive change

pupil constriction

vergence change

which muscle causes miosis

sphincter muscle

(constriction)

which muscle causes mydriasis

dilator muscle

describe the innervation pathway of the sphincter muscle

parasympathetic branch of ANS

signals originate in the Edinger-Westphal nucleus

signals travel down oculomotor nuclei

synapse at ciliary ganglion

sphincter muscle

describe the innervation pathway of the dilator muscle

sympathetic branch of ANS

signals travel down SC and along carotid artery

synapse at ciliary ganglion

dilator muscle

what are the 2 main factors of pupil size

viewing distance - near triad of accommodation

light changes

- constriction to direct illumination and illumination of opp eye (consensual response)

what are the 2 different response pathways for the pupillary light reflex

direct

consensual

describe the direct pupil response pathway

constriction of pupil that has the light shone in that eye

describe the consensual pupil response pathway

constriction of the pupil in the eye opposite to the one exposed to light

what is the role of the afferent limb of the PLR

carries sensory inputs through fibres in CNII

what is the role of the 2 efferent limbs of the PLR

carries pupillary motor outputs through fibres of CNIII and then to sphincter muscle via ciliary ganglion

which test can indicate abnormality in the PLR

Marcus Gunn's test

What is anisocoria?

unequal pupil size

what can happen if the pupil of one eye is abnormally large

parasympathetic pathway leading to sphincter muscle can be impaired

eg: midbrain / EWN, CNIII, ciliary ganglion

what can happen if the pupil of one eye appears constricted

dilator muscle b=may be impaired

eg: SC, symp pathway, defect of CNI

what are the 2 basic classes of anisocoria

physiologic anisocoria (benign)

non-physiologic anisocoria (pathologic)

describe physiological anisocoria

benign and mild form

common but idiopathic

asymmetry due to EWN

intermittent but can be persistent

no dilation lag / ptosis

describe non-physiological anisocoria

rarer forms, can indicate serious pathology

asymmetry larger

magnitude of asymmetry changes with lighting depending on abnormality

examples of efferent pathway defects

mechanical

Horner's syndrome

Aldie's tonic pupil

Oculomotor palsy

which pathway can mechanical anisocoria affect

efferent

causes of mechanical anisocoria

injury from trauma / surgery

inflammatory conditions - uveitis

PACG --> iris occlusion of TM --> distorted iris

congenital - iris coloboma

signs of mechanical anisocoria

affected pupil abnormally small

so cannot dilate under weak illumination / constrict under strong illumination

examples of drugs that can cause abnormally small pupils

pilocarpine

heroin

opioids

morphine

examples of drugs that can cause abnormally large pupils

atropine

tropicamide

cocaine, LSD, amphetamines, SSRI's

what can an abnormally small pupil be indication of

Horner's syndrome

what is Horner's syndrome be caused by

denervation of dilator

lesion along symp pathway that supplies head/neck

tumours, brainstem stroke, carotid artery dissection

what can Horner's syndrome also be associated with

ptosis in affected eye

dilation lag 15-20 secs

what can an abnormally large pupil be indicative of

Adie's tonic pupil

oculomotor palsy

migrane

what does Adie's tonic pupil result from

denervation of sphincter

what are some signs to look out for Adie's tonic pupil

light-near dissociation

tonic response

denervation supersensitvity

what is light-near dissociation

pupil constricts poorly to light but constricts normally to acommodation

what is the tonic response

sluggish redilation of pupil when going from light to dark/ after near fixation

what is denervation super sensitivity

after administering 1% pilocarpine

initially larger Adie's eye becomes smaller than normal pupil which shouldn't change size

what can oculomotor palsy be caused by

brain aneurysm, head trauma, tumour

what to do in the case of acute onset oculomotor palsy

refer!!

emergency

Describe Argyll Robertson pupil.

both pupils small and irregular but can develop at asymmetric rate

symptoms of Argyll. Robertson pupils

little constriction to light

constrict briskly to near targets

what are Argyll Robertson pupils most commonly caused by

lesion in midbrain near EWN

what are efferent pupillary defects

interfere directly with the constriction/ dilation of pupil

associated with anisocoria

what are afferent pupillary defects

impaired pupillary constriction

interfere with input of light to pupillomotor system

DONT observe anisocoria

key clinical feature of afferent pathway pupillary defects

pupils respond weakly to stimulation of diseased eye

pupils respond briskly to stimulation of normal eye

how to measure afferent pathway defect

neutral density filter in front of good eye until response if the same as through the bad eye

aetiology of afferent pathway defects

CN2 damage

ON lesions - ON, glaucoma, AION

optic tract lesions

maculopathy

amblyopia

what are the 2 way the afferent defect can present

relative - incomplete

absolute - complete

describe the absolute defect

pupils equal

near reflex normal

impaired eye stimulated = neither pupil reacts

normal eye stimulated = both react normally

caused by ON lesion

what is the defect for relative afferent defect

Marcus Gunn pupil

describe marcus gunn pupil

Afferent pupillary defect

pupil equal in size

near reflex normal

impaired eye reduced vision

impaired eye stimulated = pupils partial reaction

normal eye stimulated = both react normally

caused by partial ON lesion, not cataract