The document provides a comprehensive overview of the pupil's anatomy, function, and the pathways involved in pupillary reflexes, discussing both parasympathetic and sympathetic pathways. It also outlines various pupillary examinations and tests, as well as abnormalities such as anisocoria, Adie's tonic pupil, and Horner's syndrome, with their diagnostic implications. Lastly, it touches on congenital and acquired abnormalities affecting the pupil and the impact of pharmacological agents on pupillary reactions.

1. pupil

2. • The pupil is an opening located in the
center of the iris that allows light to enter
the retina.
• Its function is to control the amount of light
entering the eye and it does this via
contraction (miosis) and dilation
(mydriasis) under the influence of the
autonomic nervous system

3. • The iris is a contractile structure, consisting
mainly of smooth muscle, surrounding the
pupil. Light enters the eye through the
pupil, and the iris regulates the amount of
light by controlling the size of the pupil.

4. The iris contains two groups of smooth
muscles:
a circular group called the sphincter
pupillae.
and a radial group called the dilator
pupillae.

5. Parasympathetic pathway
• First Order – Retina to Pretectal Nucleus in B/S
(at level of Superior colliculus)
Second Order – Pretectal nucleus to E/W nucleus
(bilateral innervation!)
Third Order – E/W nucleus to Ciliary Ganglion
Fourth Order – Ciliary Ganglion to Sphincter
pupillae (via short ciliary nerves)
•
•
•

6. Sympathetic Pathway
• First Order – Posterior Hypothalamus to
Ciliospinal centre of Budge (C8-T2)
(Uncrossed in Brainstem)
Second Order – Ciliospinal centre of Budge to
Superior Cervical Ganaglion
Third Order – Superior Cervical Ganglion to
dilator pupillae muscle. (Close to
ICA and joins V1 intracranially)
•
•

7. Examination of Pupil

8. You can then observe the pupils closely by
shining a bright light on the patient's face from
below (minimise the shadow cast by the nose
by placing the light in the midline). If you
think there is size asymmetry, a good trick is
to stand back and observe the red reflex of
both eyes simultaneously with the
ophthalmoscope. A slight difference will then
become more apparent.

9. Pupils
• Pupil is the circular aperture in the centre of
iris. Its normal size is 3-4mm. it is grayish
black in colour.

10. Points to be noted in pupil
1. Number-normally there is one pupil.
More than one pupil is called polycoria.
2. Location- normally almost central,
slightly nasal. Eccentric pupil is called
correctopia.
3. Size of pupils

11.  Normal pupil
may be variable sizes but should be equal
– react to light
– central
– round
 Abnormal
– unequal
– dilated or constricted
– not reacting to light
– irregular (eg tear drop)
– not central

12. Assessing pupillary reflexes
• There are essentially three reflexes to
specifically test for :
Light-reflex test
Swinging flashlight test
Near-reflex test

13. Pupillary reactions


•
Pupillary Reflexes
Light reflex-
Direct- throw light into the eye, look for
pupillary constriction in the same eye
Consensual - keep an obstruction between
the two eyes. Throw light in one eye, look
for constriction in other eye.
•

14. Light-reflex test
• What it assesses - the integrity of the pupillary light
reflex pathway.
How to perform it - dim the ambient light and ask the
patient to fixate a distant target. Shine the right eye
from the right side and the left from the left side.
(Make sure you do not stand in front of the patient as
their pupils will accommodate to focus on you).
Record whether there is a direct pupillary response
(the pupil constricts when the light is shone on it) and
a consensual response (the fellow pupil constricts
too).
Normal test - there should be a brisk, simultaneous,
equal response of both pupils in response to light
shone in one or the other eye.
•
•

15. Swinging flashlight test
• What it assesses - compares direct and consensual
responses of each eye (as opposed to seeing whether
they are there or not).
How to perform it - use the same conditions as for the
light reflex test and check this reflex first. Then, move
the beam swiftly and rhythmically from one eye to
the other, making sure that you allow the same
amount of light exposure on each eye and that each is
illuminated from the same angle. You should note the
pupillary constriction of both eyes when the beam is
maintained. However, when it is swung, look at what
happens to the pupil of the eye you are concerned
about and compare this with what is happening to the
fellow eye.
•

16. • Normal test - the pupil should constrict or stay
the same size.
• If it dilates when light is shone on it, then this
means that the light reflex is weaker than the
consensual reflex (produced by withdrawing
light from the unaffected eye), suggesting
optic nerve pathology. This abnormal response
is known as a relative afferent pupillary defect
(RAPD) and is a very important sign. Note
that this is a comparative test: you cannot have
a bilateral RAPD.

18. Pupillary reactions
 Near reflex- pupil contracts while looking
at near object. It has 2 parts –
a)convergence reflex i.e. contraction of
pupil on convergence
b)accommodation reflex i.e. contraction
on accommodation

19. Near-reflex test
• What it assesses - this assesses the miosis component
of near fixation. (The other two components are
accommodation: increased lens thickness and
curvature, and convergence of the eyes).
How to perform it - in a normally lit room, instruct
the patient to look at a distant target. Bring an object
(toy, patient's thumb) into their near point (about an
arm's length away) and observe the pupillary reflex
when their fixation shifts to the near target.
Normal test - there should be a brisk constriction. A
near-light dissociation describes the situation where
the patient has a significantly better pupillary near
reflex than light reflex.
•
•

20. Abnormal pupils

21. Anisocoria
• This refers to unequal pupils. This is physiological in
about 20% of people. However, if this is a new
complaint, the steps to the underlying diagnosis lie in
determining which of the pupils is abnormal and then
look for associated signs. The first step is to compare
the pupils in light and dim conditions:
If there is a poor reaction to light in one eye and the
anisocoria is more evident in a well lit room, then the
affected pupil is abnormally large.
If there is a good reaction to light in both eyes but a
poor dilation in the dark (i.e. the anisocoria is
enhanced), then the affected pupil is abnormally
small.
•
•

22. The abnormally large pupil
• Features - there is poor constriction in a well
lit room.
• Differential diagnosis - traumatic iris damage,
third cranial nerve palsy, pharmacological
dilation (i.e. dilating drops), Adie's pupil, iris
rubeosis.

23. The abnormally small pupil
• Features - there is poor dilation in a dim room.
• Differential diagnosis - physiologically small
pupil, pilocarpine drops, uvietis with
synaechiae, Horner's syndrome.

24. Note :Dilated pupil of Left eye

25. Pupil
• Constricted (mioisis)
– Sympathetic
(pupillodilator)
denervation
– Drugs
• Pilocarpine
• Morphine
• Dilated (mydriasis)
– Parasympathetic
(pupilloconstrictor)
denervation
– Lesion of the third CN
– Drugs
• Atropine
• Cocaine

26. Shape of pupil
•
•
•
Shape normally circular
Irregular narrow pupil- iridocyclitis
Festooned pupil- irregular pupil after
patchy dilatation (effect of mydriatics in
presence of posterior synechiae)

27. The abnormally shaped pupil
• Features - a pupil should be round. Deviation
from this suggests abnormalities.
• Differential diagnosis - congenital defects
(e.g. coloboma), iris inflammation or trauma,
Argyll Robertson pupils. A fixed oval pupil in
association with severe pain, a red eye, a
cloudy cornea and systemic malaise suggests
acute angle closure glaucoma which warrants
immediate referral.

28. Irregular pupil in a case of iridocyclitis

29. The abnormally reacting pupil
 Light reflex test - abnormalities arise as a result of
severe optic nerve damage (e.g. transection) - the
patient will be blind in that eye, neither pupil reacts
when the affected side is stimulated but both pupils
react normally when the fellow eye is stimulated.
 Swinging flashlight test - when the pupil exhibits an
RAPD, it is described as a Marcus Gunn pupil. It
suggests optic nerve disease, central retinal artery or
vein occlusions ,extensive retinal lesion . A mild
RAPD may also occur in amblyopia, with vit. hg, RD
or advanced macular degeneration.

30. Near-reflex test - there are several causes of
light-near dissociation which can be grouped
according to whether the problem is unilateral
or bilateral:
• Unilateral light-near dissociation - afferent
conduction defect, Adie pupil, herpes zoster
ophthalmicus, aberrant regeneration of the
third cranial nerve.
• Bilateral - neurosyphilis, diabetes, myotonic
dystrophy, Parinaud dorsal midbrain
syndrome, encephalitis, chronic alcoholism.

31. Diseases affecting the pupils

32. Congenital abnormalities
• Aniridia - this is a bilateral condition arising from
the abnormal neuroectodermal development
secondary to genetic mutation. It is associated with
glaucoma and a number of serious, systemic
abnormalities.
Coloboma: this is an uncommon, congenital
condition characterised by a unilateral or bilateral
partial iris defect.
Leucocoria refers to a white pupil and may be due to
a number of conditions. Congenital cataracts are
generally easily identified but all patients must be
assessed for the possibility of retinoblastoma .Other
conditions causing a white pupil include persistent
fetal vasculature syndrome, Coat's disease and ROP.
•
•

33.  Acquired structural abnormalities
• Pseudoexfoliation syndrome - this is a condition characterised
by deposition of a grey-white fibrogranular extracellular matrix
material deposited on the anterior lens. It is seen, on slit-lamp
examination, as a fine grey dusting around the pupil. Pupil
shape and function are not affected - it is clinically significant
due to its association with glaucoma and its potential to make
CATARCT surgery more tricky.
Sphincter tear - iris tear can occur as a result of blunt or
penetrating trauma and can also occur during intraocular
surgery. Tears may be associated with glaucoma and, if large,
visual problems. All tears, however small, need
ophthalmological assessment.
Synechiae - this refers to adhesions between the lens and the
iris (posterior synechiae) or the iris and the peripheral cornea
(peripheral anterior synechiae). These adhesions will give rise
to an abnormally shaped pupil; treatment depends on the
underlying cause. Uveitic posterior synechiae are broken with
mydriatics whereas glaucomatous anterior synechiae may be
managed with miotics.
•
•

34. Neurological abnormalities

35. • Horner’s syndrome - this syndrome is
characterised by miosis with a pupil that is
slow to dilate, a mild (1-2mm) ptosis,
ipsilateral anhydrosis and apparent
enophthalmos (affected eye appears to be
sunken) as a result of a combination of the
ptosis and a slight elevation of the inferior
eyelid. The irides may be of different colours if
the lesion is congenital or long-
standing.Depending on the location of the
lesion, some or all of these features will be
present.

36. Horner’s
• Oculosympathetic
paresis
– Ptosis: mild (1-2mm)
– Miosis
– Ipsilateral anhidrosis
– Does not dilate with
cocaine 4%

37. Causes of Horner’s pupil
• Central – B/S lesions (tumours, vascular and MS)
• Preganglionic – Pancoast tumour, Carotid & Aortic
aneurysms, Neck lesions/trauma.
Postganglionic – Cluster headaches, Nasopharyngeal
tumours, Otitis media, Cavernous
sinus mass and ICA disease.
Miscellaneous – Congenital (brachial plexus injury)
Idiopathic.
•
•

38. • Confirmation of Horner's syndrome is with
instillation of a drop of 4% cocaine:
in physiological anisocoria, this results in
dilation whereas it doesn't where there is a
Horner's syndrome.

39. • Further localisation of the problem is carried
out with 1% hydroxyamphetamine (Paredrine).
Instillation is done >48 hours after the cocaine
test as cocaine affects the Paredrine. Pupillary
dilation suggests a central or preganglionic
Horner's syndrome whereas if dilation does
not occur, the lesion is likely to be
postganglionic.

40. • )Adie's) tonic pupil
this describes a unilateral (80% of cases)
mydriatic pupil in otherwise healthy patients
(typically young adults, especially women).
Over months to years, the pupil diminishes in
size to eventually become miotic. There is a
sluggish, sectoral or no reaction to light but a
normal near reflex. Redilation after the near-
response is slow. Slit-lamp examination may
reveal slow, vermiform contractions of the iris
but ultimately

41. • the diagnosis is confirmed by the pupil's
hypersensitivity to weak miotic drops (e.g.
0.05-0.125% pilocarpine) which causes the
abnormal pupil to contract vigorously and the
normal pupil minimally.
• Occasionally, it is associated with diminished
deep tendon reflexes (Holmes-Adie syndrome)
± autonomic nerve dysfunction.

42. • The exact cause is not known but it often
occurs after a viral illness (e.g. herpes zoster
ophthalmicus and denervation of the
postganglionic supply to the sphincter pupillae
is described. This tends to be a benign
condition and the patient is simply observed.
However, infants < 1 year old should be
referred to a paediatric neurologist to rule out
familial dystonias (Riley Day syndrome(

43. • Argyll Robertson pupil - these are caused by
neurosyphilis. Although usually
asymptomatic, they have characteristic
features on examination. These include a
bilateral (usually asymmetrical) small,
irregular pupils showing a light-near
dissociation. They are difficult to dilate.
Management is related to the underlying
disease.

44. • Argyll-Robertson
pupil
– Small, irreg
– Does not react to light
– Reacts to
accommodation
– Causes
• syphilis
• diabetes
• Miotonic pupil (Adie’s
syndrome)
–
–
Dilated
Poor response to light and
convergence.
• Constricts with weak
Pilocarpine
Holmes-Adie syndrome•
– Reduced tendon reflexes
(Knee, ankle)
- Orthostatic hypotension
comparison

45. Drugs affecting the pupils

46. Topical drugs
• Dilating - sympathomemtic e.g.
phenylephrine, adrenaline diperavine and
antimuscarinics e.g. cyclopentolate,
tropicamide , atropine.
• Constricting - muscarinic agonists e.g.
pilocarpine.

47. Systemic drugs
• Dilating - sympathomimetics e.g. adrenaline
and antimuscarinics e.g. atropine. Think also
of tricyclic antidepressants, amphetamines .
• Constricting - opiates e.g morphine and
organophosphate..