Heimann- Bielschowsky Phenomenon
The Heimann- Bielschowsky phenomenon (HBP) is a monocular vertical nystagmus characterized by slow, coarse, pendular, variable amplitude movement found in an eye with profound visual loss .The new onset vertical pendular nystagmus of HBP could be mistaken for efferent (rather than afferent disease) and might raise suspicion for a posterior fossa or brainstem lesion. 
The mechanism for HBP is currently unknown. Leigh et al. propose the pathogenesis could be related to disturbances in the fusional vergence mechanism or the monocular visual stabilization system.  The cause of the HBP can be secondary to a congenital (e.g. anterior segment dysgenesia, optic nerve hypoplasia, infantile cataract, microphthalmia, or sclerocornea) or an acquired cause (e.g. amblyopia, absolute glaucoma, optic neuropathy or a traumatic cataract). There are, however, exceptionally rare case reports of concomitant hypotropic dissociated vertical deviation (DVD; triggered by uneven visual input) and hypotropic DVD.
The HBP was first described by Ernst Heimann in 1902. He described this nystagmus occurring in amblyopia secondary to strabismus and other neurological diseases such as multiple sclerosis, neurosyphilis, and epilepsy. HBP was then distinguished as different from Dissociated Vertical Deviation (DVD) in 1931 by Alfred Bielschowsky due to DVD having better best corrected visual acuity (VA) and a slow downward drift with no nystagmoid or rhythmic movements. 
The HBP presents as a strictly monocular, coarse, slow, and pendular(which means same amplitude of movement back and forth), vertical oscillation occurring mainly in eyes with profound visual loss. The oscillations seen may be easily missed because of how slow and low frequency they present. Additionally, the pendular component ceases when active ocular motility, making the diagnostic more challenging.
Visual Loss: The HBP predominantly occurs in eyes with a large amount of visual loss. When looking at 3 studies totaling 28 patients, 24 patients had VA of 20/200 or worse. . There are recent reports of VA 20/80 after an initial insult of Optic Neuritis (initial VA 20/200) that developed ipsilateral HBV 
Wave form characteristics: The oscillations in the HBP are slow and pendular.
- Frequency: 1-5 Hz
- Amplitude: Frequently 2-5 degrees but may be as high as 20-30 degrees (40-60 prism diopters)
Diseases That Can Present Similar to the HBP:
- Spasmus nutans: A pediatric disorder consisting of a triad of ocular oscillations, compensatory head nodding, and head turning (torticollis). The nystagmus seen is small frequency. Unlike the HBP, it has a high amplitude and is usually horizontal, although it can also be vertical, rotary, and vary with different gaze positions. The nystagmus can be unilateral or bilateral and is often intermittent. Visual acuity is typically normal. 
- Ocular Neuromyotonia: A rare ocular motor disorder characterized by intermittent, tonic spasms of one or more of the extraocular muscles, resulting in strabismus and paroxysmal diplopia occurring spontaneously or after eccentric gaze lasting a few seconds up to several minutes. Most cases are unilateral and occur in adults with normal VA. 
- Acquired Pendular Nystagmus: Most commonly due to multiple sclerosis but may be a sign of a stroke or lesion in the cerebellum or brainstem. Often entails slow-phase eye movements in horizontal, vertical, and torsional planes with resultant elliptical or circular nystagmus. The movements may be monocular, or if bilateral, conjugate or disconjugate, and may also be dissociated. Cerebellar signs or brainstem signs (e.g. internuclear ophthalmoplegia) are often also present and help to differentiate from the HBP. 
- Oculopalatal myoclonus: Pendular nystagmus with concomitant palatal myoclonus (oscillations of the palate) usually developing months to years after a brainstem infarction. The eye movements are continuous with both torsional and vertical components with a frequency of 1-3 Hz. Additional muscles (pharynx, face, vocal cords, respiratory muscles, and even trunk and extremities) may be involved in this involuntary rhythmic movement that persists during sleep. 
- See-Saw nystagmus: A subtype of torsional nystagmus, is descriptively named for the pendular, vertical disconjugate movement of eyes in which one elevates/intorts while the fellow eye depresses/extorts. The frequency is usually 2-5 Hz.  
Most patients are aware that there is an intermittent oscillation but symptoms such as diplopia and oscillopsia are infrequent due to the profound visual loss usually seen in the affected eye. Although no other study reports symptoms of diplopia or oscillopsia, Davey et. al. reported 3 cases, each of which had VA better than 20/120,  and one recent case with VA 20/80 after optic neuritis. 
The HBP is a clinical diagnosis in which slow, pendular, vertical oscillations are noted in a low vision eye. It is recommended that the affected eye be observed for 1 minute. 
- Spasmus nutans
- Acquired Pendular nystagmus
- Ocular Neuromyotonia
- Oculopalatal myoclonus
- See-saw nystagmus
- Chiasmal tumor 
There is no medical therapy shown to be effective in improving the nystagmus of the HBP.
There have been mixed results when strabismus surgery is performed to try and reduce oscillations. Smith et. al. noted dampened oscillations after a Faden procedure and Sebastian et. al. noted 4 cases with large amplitude vertical oscillations that had decreased oscillations following superior rectus muscle recession with or without inferior rectus muscle recession.  Davey et. al. observed an improvement in alignment and cosmesis in 7 patients undergoing strabismus surgery, however none had reductions in oscillations. 
Vision improving surgery has not consistently shown to improve the nystagmus.
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