Pupils Flashcards
What is the pupil?
A black hole that lets light enter the eye and hits the retina
What structure of the eye absorbs the light?
Sometime the retina absorbs light directly or sometimes it’s absorbed after being reflected within the eye
Why is it important to assess pupils?
The pupil is part of the neural reflex pathway which involves the iris, retina, midbrain, parasympathetic and sympathetic system.
Assessing pupils gives information about these structures
What is the pupillary light reflex pathway?
An autonomic reflex that constricts the pupil in response to light
Describe the pupillary light reflex pathway?
Pupillary fibres are sent bilaterally to the Edinger-Westphal nuclei of the oculor motor complex. (there’s more to this)
Afferent and efferent fibres are involved
As they are sent bilaterally you get a direct and consensual reflex
What is the near triad?
The combination of 3 movements= accommodation, convergence and pupil constriction
What are these 3 movements controlled by?
The EW nucleus
What is the near triad also referred as?
Accommodation reflex
Do all 3 movements have to happen together?
No, any one of the elements of the triad can occur in the absence of the other 2
What other actions occur when the eye accomdates?
Converges and pupils constrict
How much does the pupil constrict by each dioptre of accommodation?
1 dioptre of accommodation= 0.3mm constriction
How does the near triad improve image quality?
Accommodation focuses the image
Convergence puts the image on the fovea
Pupil constriction increases depth of field, depth of focus and reducing amount of spherical aberration
How does pupil dilation (mydriasis) happen?
The dilator muscle (radial muscle) is innervated by the sympathetic bran of the ANS
How does How does pupil constriction (miosis) happen?
The sphicter muscle (circular muscle) is innervated by the parasympathetic bran of the ANS
way to remember this is constrictor=circular
What is the resting pupil affected by?
Genetics
Age (senile miosis)
What does the human pupil respond to?
Changes in illumination
Viewing near objections
Cortical influence (being excited=pupil will dilate)
What is the normal pupil size in bright light?
2-4mm (smaller)
What is the normal pupil size in dim light?
4-8mm (bigger)
What is the difference of the normal pupil between the 2 eyes?
Both pupils are generally equal in size
What should room lighting be when assessing pupils?
Ambient lighting should be reduced to exaggerate the resting pupil diameter but be of sufficient levels to allow easy viewing of the pupil, particularly in patients with very dark irises
What is Normal DCN response?
Direct
Consensual
Near
How do you test DCN responses?
If a pen-torch is presented to one eye, the pupil will constrict (the direct reflex) as will that of the other eye (the consensual reflex)
Both eyes will constrict when a patient changes gaze from a distant target to a near one (the near reflex)
How would you know pupil reactions are abnormal?
The pupil is abnormal if it fails to dilate to the dark or fails to constrict to light or accommodation.
Give an example of an afferent pupillary defect?
RAPD (also called Marcus gunn’s pupil)
What does RAPD stand for?
Relative afferent papillary defect (RAPD)
What is the problem if someone has an RAPD?
Disruption of the afferent pathway, which may be caused by damage to the retina, optic nerve, chiasma, tract or superior brachium, will result in the loss or reduction of the direct and consensual reflexes.
When can a transient (temporary) RAPD occur?
A transient RAPD can occur secondary to local anaesthesia
How do you test for an RAPD?
Swinging flashlight (Marcus-Gunn) test
If there is a lesion affecting the RE afferent fibres, what will you see?
LE direct and consensual response present (as the afferent fibres of the LE eye to the midbrain are unaffected).
Swinging the light to the RE will cause dilation of the RE (since afferent fibres relaying the direct response are affected)
If no lesion were present the RE pupil would remain constricted
If there is a lesion affecting the LE afferent fibres, what will you see?
RE direct and consensual response present
Swinging the light to the LE will cause dilation of the LE
If no lesion were present the LE pupil would remain constricted
Summarise RAPD responses
Direct reflex is absent or reduced in affected eye
Consensual reflex is normal in BEs
When you swing light over to whichever eye, it should constrict but if it dilates then there’s an RAPD in that eye
How do you record RAPD?
R RAPD
L RAPD
No RAPD
What conditions is RAPD seen in?
Optic neuritis
Retrobulbar optic neuritis due to multiple sclerosis but only for 3-4 weeks, until the visual acuity begins to improve in 1-2 weeks and may return to normal.
Very dense unilateral cataract as light scatter from the opacity may give an enhanced pupil response which appears as an RAPD in the contralateral eye.
What is a pupillary escape?
A pupillary escape is an abnormal pupillary response to a bright light, in which the pupil initially constricts to light and then slowly re-dilates to its original size
What conditions is a pupillary escape seen in?
Diseased optic nerve or retina, most often in patients with a central field defect.
Give examples of efferent pupillary defects?
Aniscoria
Holmes-Adies
Argyll-Robertson
Horner’s syndrome
What is an aniscoria?
Unequal pupil sizes (<0.4 mm difference between the 2 eyes is common and insignificant so not aniscoria)
If the pupil of one eye is abnormally larger what does this mean?
Parasympathetic pathway leading to the sphincter muscle may be less effective
If the pupil of one eye is abnormally smaller what does this mean?
Sympathetic pathway to the dilator may be impaired.
What are the 3 causes of an aniscoria?
Physiological
Efferent defect
Secondary
What is a physiological aniscoria?
Pupils that are unequal simply due to variation in anatomy. As such they are not assumed to be related to any disease process or tissue damage and the patient may simply need reassurance.
1/5th of people have different pupil sizes, usually less than 0.5mm difference in diameter. This physiological variation is confirmed by the equal response of the uneven pupils to light stimuli.
How can you tell it’s just a physiological aniscoria?
Measure the two pupils in light and then dark conditions.
The difference between each pupil diameter should stay constant whatever the ambient light level if the anisocoria is physiological.
What information can you ask the patient to aid you in determining if the aniscoria is phyisological?
Have they known about it for a length of time rather than only recently?
What size is a physiological ansicoria usually?
Small (less than 1mm)
but long-standing larger differences may also be physiological.
What secondary cause of aniscoria can there be?
Uneven pupils due to previous damage, either pathological (for example after recurrent anterior uveitis), iatrogenic (for example as a complication of intraocular surgery), pharmacological (for example as a result of asymmetric influence of a systemic drug), or age-related (as due to asymmetric atrophy of the iris muscle fibres with age).
What are efferent causes of aniscoria?
Damage to the efferent innervation of the pupil.
The main causes are
Adie, Argyll, horner and 3rd nerve palsy.
What is Holmes- Adie pupil?
Idiopathic condition which mainly affects young women. Tends to be unilateral.
(way to remember home-alone-unilateral
What is Holmes- Adie pupil caused by?
It is caused by damage to the postganglionic fibers of the parasympathetic innervation of the eye, usually by a viral or bacterial infection which causes inflammation, and affects the pupil of the eye and the autonomic nervous system.
Describe what you would see in Holmes- Adie pupil?
Dilated pupil - reaction to light is absent or slow
Constriction is slow with prolonged accommodation and slow re-dilation too
What is a test to confirm it’s Holmes- Adie pupil?
0.10% pilocarpine = very dramatic constriction
What is Argyll-Robertson?
Bilateral condition where pupils don’t respond to light
What conditions is Argyll-Robertson
seen in?
Diabetes
Neurosyphilis-infection of CNS
Describe what you would see in Holmes- Adie pupil?
No or poor constriction to light (direct and consensual responses absent)
Constriction to near object (accommodation. near response present)
What is it called when pupils accommodate but do not react light?
Light-near dissociation
(it is the absence of a miotic reaction to light, both direct and consensual, with the preservation of a miotic reaction to near stimulus (accommodation/convergence)
What is Horner’s syndrome?
The affected pupil is constricted but still retains the light and near reflexes
What are the 3 signs of horner’s
Ptosis, miosis, and (if lesion is below superior cervical ganglion) anhydrosis on the same side. The affected pupil is miosed but still retains the light and near reflexes
Steps to testing pupils during eye test
Step 1: Check for the presence of anisocoria.
• Illuminate the pupils roughly 20cm away.
If anisocoria is detected you must test in different illumination conditions.
a) to allow you to detect the abnormal pupil
b) to allow you to perform a differential diagnosis on the efferent defect that would have caused this.
Note: Anisocoria increase in dim light = sympathetic problem
Anisocoria increase in bright light = parasympathetic problem
Step 2: Check the light reaction
Ask the patient to look at non-accommodative target at 6m.
First check direct and then consensual light reflex.
Perform this at least 3x to see if the pupil is reacting properly.
After RE move onto the LE.
Step 3: The swinging-flashlight test
Shine the light on one eye for 3-4 secs, then quickly swing across to the other eye.
Repeat 3-4 times.
RAPD response:An eye with an RAPD will dilate even when direct light is shining upon it. This is because the consensual response to dilate is stronger than the direct response to constrict from the afferent pathway.
Note: if there is an equal input to brain from afferent pathway in each eye you will not get an RAPD. It is a relative difference between the input from the two eyes that can lead to responses.It is an afferent pathway defect
Step 4: Check the near reflex
This step should only be performed if pupil reactions are abnormal
Give the patient a target @ near (e.g. budgie stick line above the worst eye VA). Distance target e.g. line above the VA of the worst eye.
Patient looks at the ‘near target’ then ‘distance target’ = assess the pupil size change.Note: You can get situations where the light reflex is abnormal but the near reflex is normal. Known as: near-light dissociation.
Causes:
- Viral infections (Adie’s tonic pupil)
- Damage to the pre-tectal area (Parinaud’s syndrome)
- Damage to the rostral mid-brain (Argyll-Robertson pupil)
