Surgical Treatment of a Patient with See-Saw Nystagmus (SSN): Case Report

Background: Acquired See-saw Nystagmus (SSN) is a rare form of nystagmus characterized by elevation and intorsion of one eye with synchronous depression and intorsion of the contralateral eye in the first half cycle, followed by a reversal in the direction of the movements during the next half cycle. We herein report a case of a 47-year-old woman with a 3-year history of constant diplopia as a consequence of multiple neurosurgical interventions due to he-morrhage from a cavernous angioma located in the subthalamic region. She also had a history of major depressive disorder and ulcerative colitis. The patient underwent a surgical intervention with a 5 mm bilateral recession of the superior and inferior rectus muscles. Five years after surgery, the patient reported less recurrent and prominent episodes of transient horizontal deviation with horizontal diplopia, with a prevalence of well-being and comfort.


Introduction
The earliest known description of see-saw nystagmus was in 1913 by Maddox [1]. In clinical practice, abnormal eye movements are frequently related to brain disorders. Indeed, the etiopathogenesis of SSN is associated with a variety of acquired forms concerned with the Central Nervous System: parasellar masses [2], multiple sclerosis [3], mesodiencephalic lesions [4], radiation treatments or intrathecal methotrexate [5], and more frequently trauma [6], may result in ophthalmological disorders. Anatomically, we distinguish between mesodiencephalic lesions that affect the interstitial nucleus of Cajal and vestibular lesions that produce jerk-waveform see-saw nystagmus known as hemi-seesaw nystagmus; How to cite this paper: Sabetti, L., Murano, G. and Guetti, F. (2020) Surgical Treatment of a Patient with See-Saw Nystagmus (SSN): Case Report. Open Journal of Ophthalmology, 10, 283-287. whereas the pendular form is associated with lesions affecting the optic chiasm. The frequency of oscillation is lower in the pendular (2 -4 Hz) than in the hemi-seesaw nystagmus.
The primary goal of the treatment of SSN is to suppress the ocular oscillations and therefore to reduce the subjective visual symptoms: blurred vision, diplopia and oscillopsia. Medical treatments alone (Ethanol, Clonazepam or Memantine) have not yet yielded encouraging results and the positive effects remain fairly limited. Indeed, several common side-effects such as headache, dizziness, drowsiness, incoordination, lethargy, have been reported. Numerous treatment approaches for other forms of nystagmus exist, including: Botulinum Toxin type A The aim of this study is to evaluate the results obtained in a case of SSN treated using a new surgical technique of recession of the four vertical muscles.

Discussion
See-saw Nystagmus is a rare ocular and extremely disabling disorder due to severe oscillopsia. Although Thurtell has advocated the medical treatment of SSN with clonazepam, gabapentin or memantine [8] [9] [10], the results obtained so far have not been shown to be efficacious, particularly due to the side effects (e.g., highly impaired concentration), therefore medical therapy alone cannot be considered adequate or efficacious. The surgical procedure performed with the recession of the four vertical muscles is borrowed from the same technique involving that involves the maximum recession of all four horizontal rectus muscles applied on the nystagmus without null zone [11] [12]. The positive outcome obtained may be due to the exploitation of the primary and secondary action of the vertical muscles and to the deafferentation caused by the tenotomy and reattachment of the rectus muscles [13] [14] [15].
However, in our case, it is not possible to establish whether this results from the deafferentation or from the direct weakening of the muscle actions. The improvement reported by the patient in terms of suppression of ongoing nystagmus, the less recurrent oscillopsy (only every 10 -15 days with a duration of few minutes), the increase in visual acuity, the improvement of posture by reduction of AHP, are also confirmed at the five-year follow-up visit. This has allowed the recovery of the patient's social and work activities. The 5-mm recession of the vertical rectus muscles has not caused any pattern deviation, any cylodeviation and secondary overactions, or any alteration in the eyelid movements.

Conclusion
The new technique of recession of the four vertical muscles has yielded positive outcomes and it may be employed as a recommended procedure in similar cases. It would be desirable to compare the surgical outcomes obtained by other researchers.