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Characteristics of normal and abnormal
pupils – Part 1
Dr Janis Orr PhD, MCOptom
52
14/11/14 CET
In part 1 of a two-part series, optometrist and lecturer, Janis Orr describes the underlying pathways that serve
pupil function and provides an overview of the clinical assessments that should be undertaken as a part of a
routine eye examination.
Course code: C-38451 | Deadline: December 12, 2014
Learning objectives
To be able to obtain relevant detail from patients presenting with pupil
abnormalities (Group 1.1.2)
To be able to evaluate pupil reactions using appropriate techniques (Group 3.1.9)
About the author
Dr Janis Orr is a lecturer in optometry at Aston University where she is the leader of the further investigative techniques module. Her research
interests include refractive error development and control, optical and biometric characteristics of the eye and corneal reshaping therapy.
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Introduction
Evaluation of pupil function is a valuable
clinical test and should be assessed during
every eye examination. Through careful
assessment and knowledge of the underlying
neuronal pathways practitioners can identify
abnormalities in pupil function and determine
53
the appropriate management strategy for the
patient.
Innervation of the pupil
Parasympathetic innervation
The parasympathetic innervation of the pupil
consists of four neurons comprising afferent
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and efferent pathways (see Figure 1 page 43 ).
Afferent pathway
The first neuron connects the retina with
the pre-tectal nucleus at the level of the
superior colliculus in the mid-brain. This reflex
is mediated by the retinal photoreceptors.
Fibres from the nasal and temporal retina
travel along the optic nerve and crossover
at the chiasm. These fibres then travel along
the optic tract until they reach the pre-tectal
nucleus at the level of the superior colliculus
in the mid-brain. The second neuron connects
the pre-tectal nucleus to the EdingerWestphal nuclei. Internuncial neurones
Figure 1 The parasympathetic visual pathway. Note: the blue and red lines represent the afferent
pathway and the purple lines represent the efferent pathway
run to both ipsilateral and contralateral
Edinger-Westphal nuclei. This explains why
The first neuron starts in the posterior
(miosis) and dilate in response to darkness
a unilateral light stimulus evokes a bilateral
hypothalamus and descends down the brain
(mydriasis). Pupils react briskly to changes in
(direct and consensual) and symmetrical
stem to terminate in the cilio-spinal centre
illumination, however, mydriasis occurs more
pupillary constriction. Damage to this part of
of Budge. The second neuron passes from
slowly than miosis.
the pathway leads to light-near dissociation
the cilio-spinal centre to the superior cervical
(where the near response is normal but the
ganglion in the neck. The third neuron
population is 2–4mm in bright light and
light response is defective).
ascends along the internal carotid artery
4–8mm in dim light.1 However, the size of
until it joins the ophthalmic division of the
the pupil in certain illumination levels varies
trigeminal nerve. Sympathetic fibres travel
considerably between individuals.1
via the nasociliary nerve and the long ciliary
Normal pupil size can be influenced by a
Westphal nucleus to the ciliary ganglion.
nerves until they reach the ciliary body and
variety of other factors:
Parasympathetic fibres pass through the
dilator pupillae muscle.
• Hippus - this is the normal physiological
Efferent pathway
The third neuron connects the Edinger-
The mean range of pupil size across the
Damage to any component of the
fluctuation in pupil size. It is independent of
The fourth neuron leaves the ciliary ganglion
parasympathetic or sympathetic visual
eye movements or changes in illumination2
and passes with the short ciliary nerves to
pathways can cause abnormalities in the size,
innervate the sphincter pupillae (see Figure 2).
shape and the light reflexes of the pupil.
Sympathetic innervation
The sympathetic innervation of the pupil
Factors that influence normal
pupil size
consists of three neurons (see Figure 3
Normal pupils are round in shape and equal
page 45).
in size. They constrict in response to light
inferior division of the third cranial nerve.
• Accommodation - when an individual
accommodates, they also converge and
undergo pupillary miosis.3 This relationship is
known as the near triad4
• Senile miosis – pupil size gradually decreases
with age1, 5
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•e
nder - pupil diameter is not influenced by
gender 6
•R
efractive error - it is often assumed that
myopic individuals have larger pupils than
emmetropic and hyperopic individuals.
This has been disproved by several research
54
papers1, 6, 7
• I ris colour - pigmentation of the iris (or race)
does not influence pupil diameter1
•A
lertness and emotion - psycho-sensory
influences act on the hypothalamus (part of
the sympathetic innervation of the dilator
pupillae) via the limbic system.8, 9 Mydriasis
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can result from intense emotion, shock, pain
and heightened central nervous system
arousal.8, 9
Examination of pupil function
Figure 2 The relative positions of the sphincter and dilator pupillae muscles. The
parasympathetic and sympathetic pathways innervate the sphincter pupillae and the dilator
pupillae, respectively
When examining pupil function you must
consider:
longstanding this is much less of a concern
• The shape and position of the pupils
than if it is a novel finding. It is important to
The light response test (direct and
consensual)
• The size of the pupils
ask about visual and neurological symptoms,
The light response test is important as it
• The reaction of the pupils to light (light
for example, blurred vision, diplopia, visual
examines the integrity of the pupillary light
field loss, numbness and headaches, in order
reflex pathway.
response/reflex)
• The reaction of the pupils to accommodation
to perform an effective differential diagnosis.
(near response/reflex)
The room light should be slightly dimmed
for this test but the test must not be
The size of the pupil
performed in complete darkness, as both
Observe the size of the pupils using a direct
pupils need to be observed. Ask the patient
Shape and position of the pupil
ophthalmoscope (set at +2.00DS with a large
to fixate on a non-accommodative distant
An initial assessment of the shape and
aperture of medium brightness at a distance
target, for example the duochrome. Use a pen-
position of the pupils can be undertaken by
of 50cm). This is more accurate than simply
torch or direct ophthalmoscope as the light
general observation as the patient enters
observing the pupil with the naked eye and
source and illuminate the pupil from below
the consulting room and during history and
makes it much easier to detect anisocoria
(or temporally) at a distance of 5–10cm. Shine
symptoms. If the patient has a congenital iris
and other pupil abnormalities (particularly
the light on each pupil at least twice. First,
abnormality or a history of ocular trauma,
in patients with dark irises). Ensure that the
check the direct light response (the reaction
surgical damage or disease this is generally
beam illuminates both pupils. Pay attention to
of the pupil you are stimulating) and then the
obvious unless the irises are particularly dark.
the size, shape and centration of the pupils.
consensual light response (the reaction of the
• The swinging flashlight test.
If any abnormality of the pupil or a marked
It is important to measure pupil diameter
contralateral pupil).
difference in pupil size between the eyes
in dim and bright light, especially in the
It is good practise to repeat this test two
(anisocoria) is detected it is worth asking the
presence of anisocoria, as the difference
or three times in each eye in order to confirm
patient a few more questions about their
between the eyes can change; this is an
the direct and consensual response and to
general health and medical history. If the
important factor when determining whether
assess the influence of fatigue.
patient is aware of the abnormality and it is
anisocoria is pathological or physiological.
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Reflective learning
Having completed this CET exam, consider whether
you feel more confident in your clinical skills – how will
you change the way you practice? How will you use this
information to improve your work for patient benefit?
The near response test
they stand for and remember that you must
After performing the light response test ask
describe anomalies in detail. You must also
the patient to shift their gaze from the distant
indicate that you checked the direct (D) and
target towards a near target, for example, a
consensual light reflex (C) (light response test).
If the pupil responses are sluggish this must
budgie stick or pen tip, and then back to the
distant target again.
be noted (as normal pupil responses should
Constriction of the pupil to near fixation
be brisk, simultaneous and equal). If the pupil
but not to direct light is called light-near
reflex is absent (in one or both eyes), record
dissociation. This can be caused by viral
which eye is affected and which response is
infection, as in the case of Adie’s tonic pupil,
defective.
damage to the pre-tectal area (Parinaud’s
Thereafter, you must record the result of the
syndrome), or damage in the rostral mid-brain
swinging flashlight test. If RAPD is present,
(Argyll-Robertson pupil).
record which side is affected.
the near reflex is defective or lost when the
density (ND) filters in front of the normal
light reflex is normal. It could be argued,
eye until the swinging-flashlight test result
therefore, that you need only check the near
appears normal (unit = log units). This is not
response if the light response is abnormal.
routinely measured in optometric practice
but is worth mentioning. RAPD is always
The swinging flashlight test
in order to detect relative afferent pupillary
defect (RAPD). It is one of the most
important objective tests for the detection of
quantified in the Hospital Eye Service (HES) as
Figure 3 The sympathetic visual pathway.
The orange line represents the (efferent)
sympathetic pathway
this allows the afferent input from the afferent
visual pathway of each eye to be compared.
Since the light reflex represents the total
neuronal input, damage anywhere along
abnormalities in the afferent visual pathway.
noted that the most common error is not
this part of the visual pathway reduces the
The swinging flashlight test is often confused
shining the light on each pupil for long
amplitude of the pupil response to light.
with the Marcus Gunn test (which examines
enough (ie. less than two to three seconds).
re-dilation under sustained illumination).
It is vital that this technique is performed
Clinical Interpretation
A summary of appropriate recording of
pupil assessment is detailed in Figure 4.
carefully in order to detect RAPD using a
Firstly, record the diameter of the pupils in
Conclusion
pen-torch/direct ophthalmoscope in dim
bright and dim light (the size of the pupil can
Pupil assessment is a vital part of every routine
room lighting. It should be mentioned that
be measured using a ruler or a circular scale).
eye examination. It is simple to perform and
ophthalmologists often use head-mounted
Secondly, the shape, symmetry, reaction
effective in the differential diagnosis of disorders
binocular indirect units to examine pupils as
to light and accommodation must be
of the anterior visual pathways or the autonomic
they get a direct view of the pupil (i.e. they are
recorded. The acronym PERRL(A) can be
nervous system, which can be sight – or even life
not looking from the side of the instrument).
used: Pupils Equal Round Reactive to Light
¬– threatening. A pupil abnormality may be the
Shine the pen-torch on the right eye (from
(and Accommodation).10 Please ensure
only sign of these problems and can facilitate
below) for two to three seconds and watch the
if you use acronyms that you know what
early diagnosis and treatment.
right pupil constrict. Quickly move the light to
the left pupil (within one second) and hold the
light over the left eye for two to three seconds.
The left pupil should stay the same size or
AN
ormal pupils e.g. PERRL(A) D+C No RAPD (brisk response).
Diameter = 4mm (R+L)
dilate and quickly constrict again if RAPD is
absent.
An eye with an RAPD will dilate when the
light is shining on it as the consensual dilation
B Physiological anisocoria e.g. pupils round, reactive to light (D+C)
and accommodation. No RAPD (brisk response). Anisocoria (R>L)
Diameter: R=4mm, L=3.5mm.
response due to the light moving away from
the normal eye overpowers the poor direct
constriction response of the affected eye.
C RAPD present (in left eye) e.g. pupils round, reactive to light (D+C)
and accommodation. RAPD +ve LE 0.4log. Diameter = 4mm (R+L)
Repeat this alternation several times to check
that RAPD is definitely absent. It should be
Figure 4 Correct recording of a) normal pupils, b) physiological anisocoria, c) RAPD
14/11/14 CET
RAPD can be quantified by placing neutral
There aren’t any known conditions where
The swinging flashlight test is performed
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