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There are several pupillary abnormalities that all clinicians should be aware of. We will review the basic physiology before outlining abnormal pupillary responses and how to identify them.
Pupillary constriction:
- controlled by the parasympathetic nervous system
- achieved by a circular muscle called the sphincter pupillae
- starts at the Edinger-Westphal nucleus near the occulomotor nerve nucleus
- nerve fibers enter the orbit along with CNIII and synapse at the cilliary ganglion
Pupillary dilation:
- controlled by the sympathetic nervous system
- achieved by dilator pupillae muscles in the peripheral 2/3 of the iris
- starts at the cortex then cilliospinal (Budge's) center then down the brain stem to the cervical sympathetic chain and superior cervical ganglion then through the carotid plexus into the orbit via the 1st division of the trigeminal nerve
Pupillary exam:
- check size and shape at rest
- check the direct light response: constriction of illuminated pupil
- check the consensual light response: constriction of opposite pupil
- check accommodation: pupillary constriction when viewing a close object
- repeat on opposite pupil
Anisocoria:
- 1 pupil larger than the other
- normal in about 20% of people if less than 1mm and both eyes reacting normally to light
- may be Horner's syndrome (e.g. carotid dissection) or CNIII damage (e.g. aneurysmal expansion)
Relative Afferent Pupillary Defect (RAPD, Marcus Gunn Pupil):
- abnormal direct light response due to severe retinal diseases or optic nerve damage
- Swinging flashlight test differentiates decreased vision due to ocular issues (eg cataracts) from optic nerve problems by checking the pupillary light reflex
- in optic nerve lesions, the affected pupil won't constrict to direct light but will do so if light is shone in the other eye (consensual response)
- RAPD differentials include optic neuritis, ischemic optic or retinal disease, severe glaucoma with optic nerve damage, direct optic nerve injury (trauma, radiation, tumors), retinal detachment, severe macular degeneration, retinal infection (CMV, herpes)
Adie's (Tonic) Pupil:
- benign and common in women in their 3rd/4th decade of life
- nil or sluggish direct and consensual response to light
- thought to be from denervation in the postganglionic parasympathetic nerve
Argyll Robertson Pupil
- hallmark of tertiary neurosyphillis
- small baseline pupils which constrict with accommodation but not light
Horner's Syndrome:
- loss of sympathetic innervation with the clinical triad of ptosis (drooping eyelid), miosis (pupillary constriction) and anhidrosis (decreased sweating)
- differentials include: tumors (panacoast, nasopharyngial), carotid artery dissection, brachial plexus injury, lymphoproliferative disorders, cavernous sinus thrombosis, fibromuscular dysplasia
This information is for academic purposes only and opinions may differ. Please always use and refer to your local guidelines and protocols.
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