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What is anisocoria?

Anisocoria is the term used to describe the unequality in the size of the pupil.
The size of the pupil is controlled by muscles in the iris – the iris dilator and the iris constrictor muscles.
These muscles are controlled by nerves from the brain to the eye.
Any problems with these nerves rsults in the size of the pupil to be abnormal.
A problem with the nerve that normally dilates the pupil in the dark, causes a small pupil.
A problem with the nerve that normally constricts the pupil, produces an abnormally large pupil.
Size of pupil is determined by the following factors
  • The size of the pupil is determined by the antagonistic action of thebsphincter constrictor muscle vs the diffuse dilator pupillae
  • Parasympathetic vs Sympathetic innervation
  • Local factors may alter this
How to elicit anisocoria?
• Ask the patient to gaze at lighted window or at some other distant light source so as to
see the pupil size.
• Look for unequal pupil, associated ptosis squint, reaction to light, to detect which side is normal.
Causes of anisocoria
1.Unilateral sympathetic paralysis ? irritation
2.Unilateral 3rd nerve lesion as in
  • Brainstem damage
  • Transtentorial herniation
  • Pressure effect on 3rd nerve in tumors and aneurysm.
3. Commonest cause of anisocoria unequal pupils  is the application of mydriatic to one eye.
Causes of Pupillary inequality In bright light
(large pupil)
3rd nerve palsy
  • Trauma
  • Tumor
  • Temporal lobe herniation
  • Aneurysm
No 3rd nerve palsy
  • Drug induced
  • Adie’s pupil
  • Iris damage (trauma/surgery/laser)
  • Basal meningitis
Causes of Pupillary inequality in dim light
(small pupil)
  • Ptosis
  • Horner syndrome
  • Physiological