Although an uncommon presentation
to the eye casualty, causes of unequal pupil size ranges from benign to
life-threatening conditions. The history and physical examination are important
to determine which patients needs urgent referrals or routine clinical
appointment. The main task of the attending doctor is to exclude third
nerve palsy which requires immediate referrals as the patient may harbour
a cerebral aneurysm.
Patients may present with unequal pupils
as an incidental finding which realtived or friends comment on.
More seriously are patients who present
with sudden onset unequal pupils associated with headache +/- double vision
Determine which is the abnormal pupil,
as a rule of thumb, if the abnormal pupil is small immediate referral to
the casualty is not needed. If the abnormal pupil is the small one,
the anisocoria tends to increase in the dark; on the other hand, if the
abnormal pupil is the large one, the anisocoria increases in bright light.
A large pupil that does not respond or responds sluggishly to light is
the abnormal pupil.
Look for associated signs such as ptosis
(third nerve palsy) and abnormal eye movement (third nerve palsy).
A dilated pupil with ptosis and/or poor
eye movement should be assumed to be caused by third nerve palsy until
Also refer unequal pupils associated
with head injury to the eye casualty within 24 hours
Unequal pupils without other associated
signs can be referred to the clinic
This 70 year-old man presented with
a sudden onset left dilated pupil with ptosis and
ocular palsy. He also suffered from
headache. He was seen at the eye casualty and was
referred to the neurosurgeon. MRI
scan with contrast revealed a posterior communicating
artery aneurysm which was clipped
This man had unequal pupils with
the left pupil being smaller. Note the partial ptosis.
The patient had a left Horner's
syndrome. He was referred to the clinic for further
evaluation. In Horner's syndrome,
it is important to exclude pathological process such as
tumour in the pulmonary apex. Once
this is excluded, most cases are benign.
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