Laboratory Studies
Lab studies depend upon the specific etiology.
Imaging Studies
The use of imaging studies depends entirely upon the underlying cause of anisocoria.
Horner syndrome due to lateral medullary syndrome usually can be confirmed by MRI of the head. Imaging of the entire sympathetic pathway with MRI, CT or a combinaiton of these is common in the workup of Horner syndrome. [10]
Carotid dissection may be confirmed with magnetic resonance imaging (MRI) or angiography (MRA), computerized tomography angiography (CTA), contrast angiography, or occasionally Doppler ultrasound, depending on the segment involved, the level of suspicion, and the availability of imaging modalities. A T1-weighted MRI with fat saturation through the carotid course is very helpful sequence when dissection is suspected.
Third nerve palsies with pupillary involvement should be presumed compressive in origin. An enlarging or leaking berry aneurysm, if suggested by the presentation, is often the compressive lesion that requires most immediate diagnosis.
The choice of imaging type is dependent on the suspected pathophysiology: a cerebral aneurysm would be best imaged with angiography, while skull-based neoplasms are best demonstrated by MRI. Imaging decisions are best made in consultation with the local radiologist after a discussion including the region and lesion of interest.
Procedures
Procedures depend upon the specific etiology.
Histologic Findings
Histologic findings depend upon the specific etiology
Other Tests
Pupillometers can be used to accurately measure pupil size under various lighting conditions. [11]
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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.
