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Caryn E. Plummer, DVM, DACVO, University of Florida


|November 2013|Peer Reviewed

Pupillary Testing: Determining Which Pupil Is Affected

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Anisocoria (ie, asymmetric pupils at rest, potentially caused by ocular/neurologic disorders or pharmacologic intervention) may not be apparent at outset. Pupil response to light and dark stimulation should be checked:

  • In ambient lighting, use a dim light source held at least arm’s distance from the patient to visualize the tapetal reflection, which will delineate pupil size.
  • Darken the room and using the light source to visualize the tapetal reflection, evaluate the degree of dilation in each pupil: both pupils should dilate in darkened conditions; one pupil failing to dilate indicates the affected eye.
  • Stimulate each eye separately with a bright light: both pupils should constrict in response to bright light; one pupil failing to constrict fully indicates the affected eye.

Related Article: Top 5 Mistakes When Measuring Intraocular Pressure

CARYN E. PLUMMER, DVM, DACVO, is on faculty at University of Florida, where she completed her DVM and a residency in comparative ophthalmology. She completed her internship at Michigan State University. Her research interests include corneal disease and glaucoma. Dr. Plummer coordinates ophthalmic surgery laboratories at the NAVC Conference and has participated in the NAVC equine ophthalmology in-depth seminars and laboratories.


For global readers, a calculator to convert laboratory values, dosages, and other measurements to SI units can be found here.

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