Imaging Studies
Imaging studies
Any patient who develops nystagmus without an identifiable cause (eg, Ménière disease, drug toxicity) or with localizing neurologic deficits should undergo neuroimaging. A complete history and neuro-ophthalmic examination are crucial to localizing an intracranial disorder. Communication with the neuroradiologist regarding such localization is important in ensuring that regions of the brain suggestive of a disorder are imaged adequately.
Central vestibular forms of nystagmus are always pathologic and deserve a thorough evaluation. MRI is the preferred method of neuroimaging. Although MRI studies may be used to distinguish between central and peripheral vestibular lesions, studies have shown that examination of eye movements allows for more accurate diagnosis.
Infantile, or congenital, nystagmus typically manifests between 2-4 months of life when visual fixation normally develops and is distinct from acquired nystagmus in that it is conjugate, has mixed jerk and pendular waveforms, has a null point, and lacks oscillopsia. Visual loss, if present, is stable and not progressive. The presence of a pale optic disc, a history of progressive visual loss, or unilateral vertical nystagmus should suggest that the nystagmus is acquired and possibly due to a neoplasm involving the visual system. Such patients require neuroimaging with MRI.
Optic chiasm or third ventricle gliomas can cause a condition that mimics spasmus nutans. All children with spasmus nutans should undergo MRI imaging and a complete neuro-ophthalmic examination. Signs suggestive of a neoplastic etiology include visual acuity loss, relative afferent pupillary defect, optic disc pallor, endocrinologic abnormalities like poor feeding or dicephalic syndrome, age of onset before 12 months, and vertical or seesaw nystagmus. The neoplasm mosy commonly associated with spasmus nutans is an optic pathway glioma. [18] Lower socioeconomic status, parental drug and drug abuse, African American or Hispanic ethnicities are more associated with spasmus nutans than congenital nystagmus. [18] If the decision is made to delay MRI in children without neurologic deficit, they should be observed closely for onset of neurologic deficits.
Although not a true nystagmus because they lack slow phases and are just opposing saccades, convergence retraction nystagmoid movements are a potentially localizing eye movement disorder that is similar to nystagmus. Convergence retraction nystagmus may be elicited by having the patient look up quickly or by moving an optokinetic tape downward. [18] The deficit in upgaze results in increased signal to other muscles, including the dominant medial recti, that manifest as a convergence and co-contractions of muscles that manifest as retraction. It is a sign of pretectal dysfunction and is usually accompanied by other neurological symptoms like upgaze palsy, pupillary light dissociation and eyelid retraction. [18] Dorsal midbrain lesions may cause convergence retraction nystagmoid movements. [18]
Thyroid associated ophthalmopathy may present with eyelid retractions, decreased upgaze and globe retractions which can mimic convergence retraction nystagmus. [18] Lack of pupillary abnormalities in addition to the presence of exophthalmos, conjunctival injections, eyelid edema and positive forced ductions distinguish the two pathologies. [18]
Other Tests
Electronystagmographs record eye muscle contractions to evaluate the direction and velocity of nystagmus. It may be used to evaluate low-amplitude nystagmus that is difficult to discern on examination. This study can help determine the type and velocity of the nystagmus, which is important in directing therapy.
