Pupil assessment (9)

what is the pupil

an aperture in the iris

regulates retinal illumination 

very small (miotic) in brightly lit conditions and large (mydriatic) in dim illumination 

covered by a membrane up to the 8th month gestation

what 2 muscles does the iris contain

sphincter pupillae

dilator pupillae 

both innervated by thr autonomic nervous system : controlled by the central neural pathways that are influenced by retinal illumination , viewing distance, attention and alertness 

what is the sphincter pupillae

a ring of muscle at pupil margin

what is the dilator pupillae

a radial muscle type fibres running from the sphincter pupillae to the iris root

sphincter muscle

circular muscle

anchored to adjacent stroma and retains its function even if severed

contraction of the sphincter causes pupil to constrict in miosis.

muscle is innervated by the parasympathetic system

Afferent: to the brain - optic nerve → chiasm → optic tract → pretectal nucleus

Efferent: from the brain - ciliary gaglion → 3rd nerve → sphincter pupillae

section of iris: shows sphincter 

dilator: myoepithelium which is muscle and epithelial properies 

Afferent pathway

going from retina down the optic nerve, half goes into the brain on one side, other goes to the brain on the opposite side

fibres of sphincter muscle doesnt go too far into the brain . hits pre tectal nucleus

crosses over- so any light shon on one eye should affect both

efferent pathway

ciliary ganglion from the brain, passes the 3rd nerve then to the sphincter pupillae

dilator - innervation pathway 

dilator pupillae 

innervated by sympathetic system 

arises from the superior cervical ganglion 

lack of stimulation of sphincter causes pupils to get bigger 

starts from the central nervous system in the neck ( cervical ganglion)

both pathways in the eye

pupillary reflec pathway

pupil responses

pupil response- dilation

this is when pupil gets larger 

called dilation/mydriasis 

stimulated by sympathetic nervous system or lack of stim from sphincter 

• associated with low light 

• associated with mydriatic drugs eg tropicamide or phenylphrine , or amy sympathetic NS stimulant

• associated with excitement or fear 

pupipl response- constriction

pupil gets smaller 

miosis 

induced by the parasympatheic action on the sphincter muscle 

associated with bright light 

miotic drugs

what are the 2 types of pupil responses

direct- seen when the light enters the eye

consensual- seen when light falls in the fellow eye

pupils should react as a pair

if shine light in one eye and that pupil constricts its called direct

when shine light in one pupil and look at the other eye, thats consensual

the pupil- the near triad

accomodation - pupil constriction change when looking at distance vs near

convergence

pupil constriction

pupil size 

it is governed by a balance between the sypathetic and parasympathetic input 

methods of assessment of the pupil

done in normal room illumination

px remove glasses

look at a letter on the chart

use a spotlight if they have a vision of less than 6/18 or theyre hyperopic , to avoid stimulating accom

sit in front of the patient, dont block their view

check for size shape and location

checkng pupil size

both pupils should be equal in size

bright light: 3-6 mm in da=iameter

dim light: 4-8mm in diameter

the pupil size will show normal fluctuations known as hippus

pupil size nomally decreases with age

pupil shape 

both pupils should be round  or even slightly oval 

location of pupils

both pupils should be central in the iris

measuring pupil size

can use a ruler or pupil gauge

have ruler on forehead and as close to thr px eye as possible

reduce the room illumination but keep emough light to se the pupil margin

use a UV burton lamp if eyes are dark

do in bright and dark

repeat the pupil measurements

duchek pupil gauge 

peoce or plastic, cardboard with holes in it 

distance between holes get larger 

start from bottom 

hold the gauge as close to the eye as possible 

look through the bottom pair of holes 

the holes appear to overlap through which you can see the distance target 

move the card down. As you lool through the holes that are further apart the images will overlap less 

at some point the images will only just touch ( no black in between them) ,and youll only be able to see the distance target . this is the pupil size 

anisocoria

unequal pupil size in normal room illumination

down to physiology

direct and consensual reflexes

px fixates ahead at the chart or spot of light

shine a pen torch into the right eye (5-10cm)

position the light at the inferior temporal side

watch the right eye for constriction

note down speed and degree of response

this is direct response

do the same but watch the left pupil for constriction : consensual response

may need a burton lamp

repeat with light entering the left eye

observing the direct and consensual dilation

shine the light in the right eye as before 

observe the pupil response in both eyes when the light is removed 

it should be equal 

now repeat shining the light in the left eye 

observe the diation when the light is removed 

should be equal and smooth 

swinging flashlight test- RAPD

checks the afferent pathway to the brian

the patient fixates in the distance

holds the pentorch below the right eye (5-10 cm) for 2-3 secs 

quickly move the light over to the same position but below left eye 

keep the position below the eye 

pause for 2-3 seconds 

repeat several times

observe the pupil size as the light is swung backwards and forwards 

swinging flashlight test results

• normal

pupil constricts as light enters the eye

briefly dilates as torch swings to other eye

re constricts as conselsual reflex occurs

• abnormal

the pupil of the effected eye will appear to dilate when the light falls on it

afferent pupil defects: absolute 

with light in one eye, both eyes constrict 

swap over to other eye- pupil gets bigger in both eyes 

left absolute defect- dilating back to what it was in normal room illumination , no stimulus is affecting the eye 

when light is shon into the affected eye, both pupils dilate slightly because less afferent signal is sent 

afferet pupil defect- relative

when illuminating one eye, both eye constricts

when illuminating other eye, dilates slightly but doesnt go back to the normal room illumination

less signal is sent ot the brain

positive RAPD

relative to the response in the right eye- left 

how to dteermine the affected eye for RAPD 

shine light in one eye for 2-3 seconds 

observe both pupils 

normally, both pupils constrict 

swing the light to the other eye and observe 

if the pupils dilate when light is shining into the left eye fo rexample, then the left eye is affected 

the near reflex ( reading response)

often tested if a problem is found with the light responses

px fixates into the distance

ask the px to fixate a near target 15cm away

dont use pentorch as target

observe the pupil constriction as the px look sat the near target

observe the dilation as the px returns their gaze to the distance

pupil defects

what are the 2 types of pupil defects 

afferent- signal impaired going to the brain 

efferent- signal impaired coming from the brain

afferent pupil fibres

starts at the retina. photoreceptors detect the light and signals travel through bipolar cells → ganglion cells

travels to optic nerve which caries all visual and pupillary light reflex signals from one eye

goes to optic chiams, where around 505 of fibres from nasal retina cross to the opposite side

optic tract- contains fibres from both eyes, each optic tract carries info from contralateral visual field . pupillary fibres remain in the tract bt peel off begore reaching the LGN ( lateral geniculate body)

goes to the pretectal nuclues- midbrain: this is where the afferent signal for pupil reflec synapses

creates a direct and consensual response

afferent pupil defects

the pupils are equal size in normal room illumination

recording:

RAPD present / RAPD not present

or positive RAPD / negative RAPD

efferent pupil fibres 

motor pathway that carries signals from the brain to the eye making the pupil constrict 

1. edinger westphal nuclues located in midbrain, recieves input from both pretectal nucleus and sends paasympathetic fibres to control pupil constriction

2. the parasympathetic fibres travel superficially on outside of oculomotor nerve, 

3. oculomotor nerve synapse at the ciliary ganglion 

4. post ganglionic fibres leave ciliary ganglion and travel via short ciliary nerves to the eye 

5. reaches the iris sphincter muscle and the parasym activates causing pupil to constrict 

6. iris dilator is via long ciliary nerves

fixed miotic pupil defects

horners

iritis

argyll robertson

long standing adie

pharmacological

fixed mydriasis pupil defects

trauma

adie

acute ACG

third nerve palsy

pharmacologcal

efferent pupil defects 

adie or tonic pupil- large pupil

loss of input from ciliary gangliato sphincter - where the sphincter muscle gets its innervation

unopposed dilator action 

adie pupil

80% unilateral

young adults typically affected usually female 

other associations like temporal arteritis, diabetes 

third nerve palsy

large pupil - sphincter pupillae innervated by the third nerve, so if anything affecting the third nerve causes the large pupil

thrd nerve also controls ocular muscles and levator muscle

so get droopy lids, eye goes down and out

refer to hospital

efferent pupil defects: horners

horners syndrome- loss of input from the sympathetic ganglia

unopposed sphincter action

smaller pupil

dilator muscle paralysed

any age

associated with poor dilation, ptosis and facial anhydrosis

check up routinely 

ptosis 

drooping of the upper eyelid 

if ptosis is on the same side as miotic pupil: horners 

is ptosis is on same side as mydriatic pupi: third nerve palsy 

miotic pupil conditions : argyl and iritis

argyl: pupils so not constrict to light but do when focusing on near objects

iritis : red eye , pain , constricted pupil , cells and flar in anterior chamber

mydriatic pupil : acute angle close glaucoma

fixed diated pupil in acute angle closure glaucoma

linked to IOP and drainage of aq humour

the pupil resonse- recording 

pupil size in mm 

pupil shape 

pupil reflexes- direct and consensual 

speed of response may also be added on a scale of 0 ( no response) - 4 ( large brisk response)

check and note for RAPD , either ±

PERRLA: recording

P: pupils

E: equal

R: round

R: reactive

L: light

A: accom - only check ifresponse to light was not normal

both the pupils constrict, which eye is showing a consensual resonse

left

both pupils dilate, which eye is blind?

the right, as light is shining into it

what is unequal pupil size in normal lighting conditions called?

anisocoria

what causes a small pupil

horners

constriction of pupil sphincter muscle causes what

pupil constriction 

miosis ( another word for pupil constriction)

stimulation of the sympathetic nervous system causes what?

both pupils to dilate

parasyn: causes both pupils to constrict