From the Department of Ophthalmology, Harvard Medical School, Massachusetts Eye & Ear Infirmary, Boston, Massachusetts.
The authors have no financial or proprietary interest in the materials presented herein.
Address correspondence to Dean M. Cestari, MD, Neuro-ophthalmology Service, Department of Ophthalmology, Harvard Medical School, Massachusetts Eye & Ear Infirmary, 243 Charles Street, Boston, MA 02114. E-mail: email@example.com
See-saw nystagmus is an uncommon disorder that can be acquired or congenital and consists of cycles in which one eye rises and intorts while the other depresses and extorts, followed by reversal of the pattern.1 The acquired form is usually secondary to suprasellar masses,2,3 and is seen less commonly in head injury,4 brainstem infarction,5 and multiple sclerosis.6 In rare cases, severe visual loss alone may cause this eye movement disorder.7 Treatment options are limited and often unsatisfactory, leaving the patient with bothersome illusory movements of the environment (ie, oscillopsia). We report the case of a patient with acquired see-saw nystagmus whose oscillopsia was successfully treated with the injection of onabotulinum toxin A to the inferior oblique and superior oblique muscles of his right eye, combined with occlusion of the left eye.
The patient was a 68-year-old man who was referred because of nystagmus. He had hypertension and congestive heart failure, but prior to 1999, his only eye problem was refractive and his neurological history was negative. In 1999, he developed a left hemiparesis secondary to an ischemic infarction in a nonspecified brain area. In 2000, he suffered a stroke that caused “only” an eye movement disturbance. Following a third stroke in December 2006, the eye symptoms worsened and dysarthria developed. He reported that “the eyes are going up and down” and that he saw the world in constant motion. Because of oscillopsia, he was unable to watch television, read, or even sign his name.
Neuro-imaging showed multiple brainstem infarctions. His medications included atenolol, furosemide, lisinopril, glipizide, clopidogrel bisulfate, clonazepam, pantoprazole, and duloxetine.
On examination, the patient was wheelchair bound, overweight, dysarthric, alert, oriented, calm, and cooperative. Corrected visual acuities were 14/20+1 in the right eye and 14/100+1 in the left eye, but constant movement of the eyes made testing difficult. Confrontation testing showed full fields to finger movements in each eye. There was no ptosis or eyelid retraction and he had blepharitis of both eyes. The pupils were round, equal, and reacted normally. His head was tilted toward his left shoulder secondary to spasticity from the left hemiparesis. Ductions were full, but there was a disconjugate and dissociated see-saw nystagmus with much greater vertical excursion of the left eye. He also had synchronous palatal and facial contractions. His fundi were normal.
Onabotulinum toxin type A was injected into the extraocular muscles under electromyographic guidance, 5 international units into the right inferior oblique muscle and 2.5 international units into the right superior oblique muscle, without complication.
Three weeks after injection, visual acuities were unchanged but his ability to read the eye chart was much improved. Furthermore, there was an obvious decrease in the frequency and amplitude of the torsional component of the nystagmus with a subtle decrease in the amplitude of the vertical excursion in the right eye. There appeared to be an exacerbation of the amplitude and frequency of both the torsional and vertical components of the nystagmus of the left eye. While patching the left eye, the patient and his family reported a tremendous improvement in his symptoms. He was subsequently able to watch television, read, and sign his name on a piece of paper. He is seen regularly at 4-month intervals for repeat injections.
See-saw nystagmus is a pendular oscillation that consists of elevation and intorsion of one eye and depression and extorsion of the fellow eye that alternates every half cycle. It can be pendular-waveform or jerk-waveform. Pendular-waveform see-saw nystagmus is commonly due to a midline meso-diencephalic, bilaterally compressing mass. Jerk-waveform see-saw nystagmus is mostly due to a unilateral lesion in the meso-diencephalic junction and is theorized to be secondary to a unilateral lesion of the interstitial nucleus of Cajal sparing the rostral interstitial nucleus of the medial longitudinal fascicle 3. See-saw nystagmus can also be seen in patients with chiasmal lesions, suggesting loss of the crossed visual inputs from the decussating fibers of the optic nerve at the level of the chiasm as the cause. Interestingly, a see-saw component is present in many forms of central nystagmus and it has recently been recognized that subclinical see-saw nystagmus can be present with congenital nystagmus.8
Patients with acquired forms of nystagmus typically experience oscillopsia that can be severely debilitating and often interferes with activities of daily living. Medical treatment of see-saw nystagmus has been attempted with clonazepam, gabapentin,7 and ethanol9 with limited success. Surgical treatment options are limited, but Averbuch-Heller et al. have shown that surgically tenotomizing and immediately reattaching the horizontal and vertical recti muscles, performed in a staged procedure, can damp nystagmus in an animal model of congenital and see-saw nystagmus by interfering with the proprioceptive feedback loop.10 This treatment has also been shown to have some success in humans.11
However, given the limited and variable success of the available medical and surgical treatment options for the debilitating symptoms of oscillopsia, we anticipated that fogging the left eye in conjunction with a careful injection of onabotulinum toxin A to the primary cyclotorters (inferior oblique and superior oblique muscles) of the right eye would help to stabilize the torsional component of the see-saw nystagmus in our patient and improve his visual function. Our patient’s see-saw nystagmus showed greater amplitudes of cyclotorsion and vertical deviation in the left eye, which is why we chose to inject the cyclotorters of the right eye and patch the left eye (injecting both eyes is impractical given the imprecise effects of onabotulinum toxin A in causing muscle paresis, and small differences will cause disconjugate eye movements and will result in binocular diplopia).
We injected a smaller volume of toxin into the superior oblique muscle to decrease the risk of inadvertently causing ptosis from spread of the toxin to the levator palpebrae muscle (spread of toxin outside of the intended muscle is thought to occur more commonly when larger volumes are used), although it would have been a reasonable alternative to use a higher concentration in the same volume as that used in the inferior oblique muscle. We suspect the apparent worsening of nystagmic excursion in the left eye following the extraocular onabotulinum toxin type A injection in the right eye is secondary to Hering’s law of equal innervation.
Prior to injecting onabotulinum toxin in the right eye, we tried patching of the left and right eyes individually without improvement in our patient’s symptoms. Although we were not able to record an improvement in visual acuity on the Snellen chart, we want to emphasize that this patient could intermittently read letters at 14/20 with difficulty and only after much effort prior to the onabotulinum toxin A injections. Following the injections, however, he could consistently read the letters much more quickly and with significantly less effort.
The results of our case suggest that weakening the superior oblique and inferior oblique muscles with onabotulinum toxin A in certain patients with symptomatic oscillopsia from see-saw nystagmus can decrease the amplitude and frequency of the torsional component of the nystagmus with subsequent improvement in a patient’s visual distress and activities of daily life.
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