Abnormalities of the Pupil
The CMGs are guidelines on the diagnosis and management of a range of common and rare, but important, eye conditions that present with varying frequency in primary and first contact care.
The CMGs are guidelines on the diagnosis and management of a range of common and rare, but important, eye conditions that present with varying frequency in primary and first contact care.
Although pupil anomalies are commonly benign, they may be the first or only manifestation of a serious or even life-threatening disorder.
Physiological (‘simple’) anisocoria
Tonic (Adie’s) pupil
Horner’s syndrome
Argyll Robertson pupil
Tonic pupil
Horner’s syndrome
Argyll Robertson pupil
Generally asymptomatic, although pupil abnormalities may be associated with pain, photophobia or visual disturbance
Ipsilateral orbital, face, or neck pain has been reported in up to 58% of cases of Horner’s syndrome associated with internal carotid artery dissection
Physiological (‘simple’) anisocoria
Tonic (Adie’s) pupil
Horner’s syndrome
Argyll Robertson pupil
Condition | Pupillary signs | Associated features |
Physiological anisocoria |
Unequal pupil sizes ≥0.5mm but <1mm. Asymmetry similar in light and dark conditions |
None |
Tonic pupil | Affected pupil larger. Decreased response to light but normal near response |
Usually idiopathic. |
Horner’s syndrome |
Miosis of affected pupil | Mild ptosis and anhydrosis on affected side. Heterochromia if congenital |
Argyll-Robertson pupil | Bilateral miosis. Minimal or no reaction to light but normal near response |
Neurosyphilis (rare manifestation) |
Mechanical causes such as posterior synechiae, iris sphincter tears, or surigcal injury
Mid-dilated pupil in acute angle closure crisis
Third nerve palsy
Practitioners should recognise their limitations and where necessary seek further advice or refer the patient elsewhere
For physiological anisocoria, old photographs can be diagnostically helpful
(GRADE*: Level of evidence=low, Strength of recommendation=strong)
Initial slit lamp assessment to exclude mechanical causes such as posterior synechiae or iris sphincter tears
(GRADE*: Level of evidence=low, Strength of recommendation=strong)
Pharmacological testing is of limited value due to poor availability of the reagents and high false positive and false negative rates.
(GRADE*: Level of evidence=low, Strength of recommendation=strong)
B2: alleviation/palliation; normally no referral
B1: Refer to ophthalmologist or neurologist.
Often requires investigation and management by multi-disciplinary team
*GRADE: Grading of Recommendations Assessment, Development and Evaluation (see http://www.gradeworkinggroup.org/index.htm)
Sources of evidence
Davagnanam I, Fraser CL, Miszkiel K, Daniel CS, Plant GT. Adult Horner's syndrome: a combined clinical, pharmacological, and imaging algorithm. Eye (Lond). 2013;27(3):291-8.
Gross JR, McClelland CM, Lee MS. An approach to anisocoria. Curr Opin Ophthalmol. 2016;27(6):486-492.
Lam BL, Thompson HS, Corbett JJ. The prevalence of simple anisocoria.Am J Ophthalmol. 1987;104(1):69-73.
Martin TJ. Horner's syndrome, Pseudo-Horner's syndrome, and simple anisocoria. Curr Neurol Neurosci Rep. 2007;7(5):397-406.
Moeller JJ, Maxner CE. The dilated pupil: an update. Curr Neurol Neurosci Rep. 2007;7(5):417-22.
Wilhelm H. Disorders of the pupil. Handb Clin Neurol. 2011;102:427-66.
The pupil (the circular black area in the middle of the coloured part of the eye) is usually the same size as the pupil on the other side, and the two pupils usually react together (for example to light). The pupils have muscles to constrict them (make them smaller) and muscles to dilate them (make them larger) and these are controlled by a network of nerves from the brain which works automatically. We all know that bright light makes the pupils smaller and dim light makes them larger. This makes a 20-times difference to the amount of light entering the eye. The pupils also constrict when we look at near objects (for example when we read), which makes focusing easier.
Normally this system works well, without our being aware of it, but there are many ways in which control can be lost. In a fifth of people, the pupils are usually slightly different in size (‘physiological anisocoria’). This is not a problem.
In 1 in 500 people, the nerves that control pupil constriction in one eye do not work properly (Tonic or Adie’s pupil). Usually a cause cannot be found, but rarely this can affect people following an infection or surgery to the eye socket.
In another condition, there is a small pupil on one side, a drooping of the upper lid, and no sweating on the same side of the face. This is known as Horner’s syndrome. It can occur in babies who are injured during birth, and in people with disease of the blood vessels, cancer or following some types of operation.
In Argyll Robertson pupil, both pupils are small and there is no reaction to light, but constriction for looking at near objects still happens. This condition is usually seen at a late stage of the sexually-transmitted infection syphilis and shows that the disease has affected the nervous system.
The optometrist who finds one of these conditions will either take no action, having explained the findings to the patient, or refer the patient to the ophthalmologist or neurologist if tests are needed.
Abnormalities of the pupil
Version 1
Date of search 24.01.20
Date of revision 28.01.21
Date of publication 22.03.21
Date for review 23.01.22
© College of Optometrists
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