Overview
Anisocoria is the term used to describe unequal pupils. It can be physiological and harmless in around 20%. New-onset anisocoria can suggest underlying pathology. The pupils should not vary by more than 1mm in size and both eyes should react to light normally.
Anisocoria can demonstrate problems with the efferent pupillary pathway.
Unilateral Large Pupil
This is due to a pupil failing to constrict properly in a well-lit room, indicating a problem with the parasympathetic efferent pathway. Some causes are:
- Third cranial nerve palsy
- Rubeosis iridis
- Holmes-Adie syndrome
- Drug-induced
Unilateral Small Pupil
This is due to a pupil failing to dilate properly in a room with low light, indicating a problem with the sympathetic efferent pathway. Some causes are:
- Physiologically small pupil
- Horner’s syndrome
- Argyll Robertson (AR) pupil
- Uveitis
- Drug-induced
