Medication Summary
Drugs commonly used in the diagnosis of anisocoria include cocaine, apraclonidine, hydroxyamphetamine, and pilocarpine (0.1-1%).
Topical anesthetic agents
Class Summary
This agent is used for diagnostic testing to detect Horner syndrome.
Cocaine
Prevents norepinephrine reuptake and accordingly dilates eye with intact sympathetic nervous system supply. Decreases membrane permeability to sodium ions, which, in turn, inhibits depolarization and blocks conduction of nerve impulses.
Cholinergic agents
Class Summary
This agent is used for diagnostic testing related to tonic pupil (0.1% concentration) or pharmacologic dilation-induced anisocoria (1% concentration).
Pilocarpine ophthalmic (Isopto)
Does not normally constrict pupil; however, with tonic pupil, produces miosis due to cholinergic supersensitivity. Constricts normal pupil or mydriatic pupil due to oculomotor palsy; however, after pharmacologic dilation (eg, atropinelike agents), pilocarpine has no miotic effects.
Sympathomimetic agents
Class Summary
Hydroxyamphetamine is useful diagnostically to test integrity of the third-order sympathetic neuron.
Hydroxyamphetamine (Paredrine)
Dilates pupil if third-order sympathetic neuron intact, and fails to dilate pupil if third-order neuron impaired.
Alpha2-adrenergic agonist agent, ophthalmic
Class Summary
These agents decrease IOP by reducing aqueous humor production.
Apraclonidine (Iopidine)
Potent alpha-adrenergic agent selective for alpha2-receptors with minimal cross-reactivity to alpha1-receptors. Suppresses aqueous production. Reduces elevated, as well as normal, intraocular pressure (IOP) whether accompanied by glaucoma or not. Apraclonidine is relatively selective alpha-adrenergic agonist that does not have significant local anesthetic activity. Has minimal cardiovascular effects.
Due to the weak, direct alpha-1 and alpha-2 receptor agonist effect, apraclonidine may reverse the Horner anisocoria (no effect on normal pupil, but Horner syndrome-related denervation supersensitivity produces pupil dilation).
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Flowchart to assist in the diagnosis of anisocoria (modified with permission from Thompson and Pilley)
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Horner syndrome secondary to carotid dissection. Note that degree of anisocoria is relatively mild in room light. Also, see the image below of the same patient.
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Horner syndrome due to carotid dissection. Note the increase in degree of anisocoria under dark conditions.
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Typical pupil in third nerve palsy, with mydriasis. Note the inability to adduct the right eye. This patient has a skull-based meningioma that is compressing the right third nerve. At rest, complete ptosis is present in the right eye; however, lid elevation with attempted adduction of the right eye is noted, which is consistent with aberrant regeneration.
