From Dog

Anisocoria (inequality of pupil size) may arise as a result of abnormalities of the eye, the oculosympathetic system, the light reflex pathway, the midbrain or the cerebellum.

The underlying cause is not always obvious, particularly in relation to inflammatory disorders and detailed investigations may be required. It is important to detect which eye is abnormal when anisocoria is present, and this may require careful observation of direct and consensual pupillary light reflexes and pupillary dilation in response to low light conditions.

Causes of anisocoria include:

  • congenital or acquired iris problems (e.g. iris hypoplasia, iris atrophy and iritis), glaucoma and fundus abnormalities should be considered.
  • inequality of pupil size due either to miosis (constricted pupil) or mydriasis (dilated pupil)
- Ocular neoplasia (e.g. lymphoma, adenocarcinoma)
- Anterior uveitis
- Otitis media
- Horner's syndrome
- Retinal detachment - unilateral
- Uveodermatologic syndrome
- Toxins - e.g. organophosphates, parasympathomimetic drugs
- Degenerative - e.g. iris atrophy, spongiform encephalopathy, encephalitis
- Thiamine deficiency