Pupil Pathologies 2 Flashcards
What is an example of an efferent pathway pupillary defect?
Anisocoria (uneven pupil sizes)
From an assessment of anisocoria how can we determine which system, sympathetic or parasympathetic, is affected?
- If the pupil of one eye is abnormally large the parasympathetic pathway leading to the sphincter muscle may be impaired
E.g., due to a defect in the midbrain (e.g., Edinger-Westphal Nucleus), CN3, ciliary ganglion, or the iris itself
- If the pupil appears constricted the sympathetic pathway to the dilatator may be impaired.
E.g.,due to a defect anywhere along the sympathetic pathway, from spinal cord to iris
How can we classify anisocoria?
By whether it is Physiologic (benign) or non-physiologic (pathologic).
What is physiologic anisocoria also called?
Simple anisocoria
What is Simple anisocoria?
What is its prevalence?
What is its cause?
How big does the pupil size difference tend to be?
How does it present?
A common and benign form of mild anisocoria
Relatively common (around 20% of healthy people)
Idiopathic (cause unknown), though asymmetrical inhibition of the Edinger-Westphal nucleus is suspected to play a role.
Typically, the asymmetry is small in magnitude (typically < 0.6 mm difference in diameter)
Typically intermittent (i.e. may only be present in certain conditions or at certain ages), but can be persistent
Relative difference between both eyes often does not change substantially in response to changes in ambient light (though sometimes more pronounced in low light)
Isolated: eye otherwise normal, with normal light response, no dilation lag, and no ptosis
How can pathologic anisocorias be subclassified?
By the cause, i.e. mechanical (relating to iris muscles) or extraocular (relating to factors outside the eye)
What is mechanical anisocoria?
Mechanical disorders of the iris & supporting structures which cause unequal pupil size
What are possible causes of mechanical anisocoria?
- physical injury from ocular trauma or surgery (incl. cataract extraction)
- inflammatory conditions such as iritis or uveitis
- angle closure glaucoma leading to iris occlusion of the trabecular meshwork (dilated, unresponsive pupil)
- intraocular tumors causing physical distortion of the iris.
- Various congenital defects (e.g., aniridia, iris coloboma, congenital ectopic pupils, polycoria, etc.)
How may mechanical anisocoria present?
The affected pupil may be abnormally small (i.e., fails to dilate under weak illumination), or, in the case of David Bowie, abnormally large (i.e., fails to constrict under strong illumination).
What are some non-physiologic extra-ocular causes of anisocoria?
Pharmacological anisocoria
Horner’s syndrome
Adie’s tonic pupil
Oculomotor nerve palsy
Describe the causes of pharmalogical anisocoria, including how it can present and an example of which common drugs may cause it
- Abnormally small pupils can result from miotic eyedrops such as pilocarpine, used to treat glaucoma (i.e., particularly if the treatment is unilateral); & opioids such as heroin & morphine
- Abnormally large pupils can result from mydriatic (‘anticholinergic’) eyedrops such as atropine & tropicamide, which can cause the pupil to dilate by 8 mm or more. Smaller dilatation (~1-2 mm) can also result from various ‘sympathomimetic’ drugs such as cocaine, LSD, and amphetamines
…Also SSRIs for depression, patches to treat nausea from motion-sickness/chemotherapy, some pesticides, aerosolized anticholinergic drugs administered through ventilator masks, certain plants (e.g., jimsonweed)… etc.
What is Horner’s syndrome?
An interruption of nerve supply from the brain to the face and eye, on one side of the body.
How can Horner’s syndrome cause anisocoria?
Caused by denervation of the dilator…
…due to a lesion anywhere along the sympathetic pathway that supplies the head, eye, and neck.
What are some causes of Horner’s syndrome and as a result causes of anisocoria caused by Horner’s syndrome?
Often idiopathic, but causes include tumors, brain stem stroke, and carotid artery dissection (the most common cause of stroke in young adults)
How does anisocoria caused by Horner’s Syndrome present?
Often associated with a small (1-2mm) amount of ptosis (in the affected eye only, due to denervation of Müller’s muscles), and a dilation lag of 15 to 20 seconds. Also, facial anhydrosis (loss of sweating)
How can we confirm a suspicion of anisocoria caused by Horner’s syndrome (as the miosis tends to be subtle)?
The miosis (anisocoria) may be subtle, and require a dark room to be visible. It can be enhanced by applying cocaine (which, unlike in physiologic anisocoria, causes the normal pupil only to dilate)
What causes Adie’s tonic pupil and how does it present (and manifest overtime)?
Adie’s tonic pupil results from denervation of the sphincter
In the acute phase, findings may be isolated to unilateral mydriasis with poor light reactivity. Over weeks may also observe:
- Light-near dissociation. The pupil constricts poorly to light but reacts better to accommodation (near response) [See picture]
- Tonic response. When going from light to dark, or after near fixation, the pupil redilates very slowly (‘sluggish’).
- Denervation supersensitivity. Following two drops of dilute pilocarpine (0.1%) in each eye, the initially larger Adie’s pupil becomes smaller than the normal pupil, which does not usually change in size.
What is an example of an efferent pupillary defect that affects both eyes?
Argyll Robertson pupils:
Both pupils small (<2mm) and irregular, though can sometimes develop at an asymmetric rate
Little constriction to light, but constrict briskly to near targets (light-near dissociation)
(though overtime the pupil becomes permanently immobile)
Most commonly due to a lesion in the midbrain near the Edinger-Westphal nucleus
Characteristic of syphilis (now uncommon)
What are key clinical features of an afferent pupillary defect?
: Both pupils respond weakly to stimulation of the diseased eye and briskly to stimulation of the normal eye (i.e., the Markus Gunn / swinging light test)
[Observe pupil sizes]
