Magnetic Oculomotor Prosthetics for Acquired Nystagmus

Abstract

PurposeAcquired nystagmus, a highly symptomatic consequence of damage to the substrates of oculomotor control, often is resistant to pharmacotherapy. Although heterogeneous in its neural cause, its expression is unified at the effector—the eye muscles themselves—where physical damping of the oscillation offers an alternative approach. Because direct surgical fixation would immobilize the globe, action at a distance is required to damp the oscillation at the point of fixation, allowing unhindered gaze shifts at other times. Implementing this idea magnetically, herein we describe the successful implantation of a novel magnetic oculomotor prosthesis in a patient.DesignCase report of a pilot, experimental intervention.ParticipantA 49-year-old man with longstanding, medication-resistant, upbeat nystagmus resulting from a paraneoplastic syndrome caused by stage 2A, grade I, nodular sclerosing Hodgkin's lymphoma.MethodsWe designed a 2-part, titanium-encased, rare-earth magnet oculomotor prosthesis, powered to damp nystagmus without interfering with the larger forces involved in saccades. Its damping effects were confirmed when applied externally. We proceeded to implant the device in the patient, comparing visual functions and high-resolution oculography before and after implantation and monitoring the patient for more than 4 years after surgery.Main Outcome MeasuresWe recorded Snellen visual acuity before and after intervention, as well as the amplitude, drift velocity, frequency, and intensity of the nystagmus in each eye.ResultsThe patient reported a clinically significant improvement of 1 line of Snellen acuity (from 6/9 bilaterally to 6/6 on the left and 6/5–2 on the right), reflecting an objectively measured reduction in the amplitude, drift velocity, frequency, and intensity of the nystagmus. These improvements were maintained throughout a follow-up of 4 years and enabled him to return to paid employment.ConclusionsThis work opens a new field of implantable therapeutic devices—oculomotor prosthetics—designed to modify eye movements dynamically by physical means in cases where a purely neural approach is ineffective. Applied to acquired nystagmus refractory to all other interventions, it is shown successfully to damp pathologic eye oscillations while allowing normal saccadic shifts of gaze.

Nystagmus

“…For channelopathies as familial hemiplegic migraine, acetazolamide is effective for treating ] and resting in darkness for 2 h (compared with remaining in bright light), resulting in a relative reduction of vertical slow-phase eye velocity by about one-third [73]. Advanced therapeutic interventions in acquired nystagmus include the attachment of a T-plate to the lateral orbital rim and the inferior rectus muscle tendon [74], the implantation of an oculomotor prosthesis [75] and retrobulbar botulinum-toxin A injections [76], resulting in reduced nystagmus amplitude and oscillopsia in all cases. Lateral canal occlusion was confirmed as a valuable treatment option for headshaking nystagmus and vertigo in a patient with head-jolting nystagmus syndrome [77].…”

Stability andin vivosafety of gold, titanium nitride and parylene C coatings on NdFeB magnets implanted in muscles towards a new generation of myokinetic prosthetic limbs

“…For this reason, they have been suggested for a wide range of biomedical applications that require wireless tracking of movements and minimally invasive interventions. In particular, permanent magnets were used as key-components in several implantable devices 1 ranging from cochlear, 2 dental 3 and ocular implants, 4 to urinary 5 and gastroesophageal sphincters 6 and even more complex, fully implantable artificial organs. 7 This also concerns the field of limb lengthening 8 and prosthetics.…”

“…Among these, titanium (Ti) presents good biocompatibility, anti-biofilm and osteogenesis activity in bone implants. 14 NdFeB magnets encapsulated in titanium (Ti) cases demonstrated to favor their implant in ear bones, 15 eye muscles 4 and gastrointestinal tissues 16 , 17 in terms of stability and biocompatibility. Nonetheless encapsulation within Ti cases significantly increases the grade of complexity of the fabrication process, as well as the invasiveness of the implantation procedure due to the case encumbrance (without increasing the volume of the magnetic material).…”

Trend and prospect of the magnetic surgery

“…Kim等人 [30] . [58] . (a) 眼下直肌下方植入一枚直径3 mm、厚度1 mm的柱形钐钴磁体; (b) 在眶底上方植入一枚直径3.73 mm、厚度2 mm的柱形钕铁硼磁体; (c) 术后X射线片 Figure 4 (Color online) Magnetic damping technique used to treat nystagmus (right eye) [58] .…”

“…[58] . (a) 眼下直肌下方植入一枚直径3 mm、厚度1 mm的柱形钐钴磁体; (b) 在眶底上方植入一枚直径3.73 mm、厚度2 mm的柱形钕铁硼磁体; (c) 术后X射线片 Figure 4 (Color online) Magnetic damping technique used to treat nystagmus (right eye) [58] . (a) Implant a cylindrical samarium cobalt magnet with a diameter of 3 mm and a thickness of 1 mm below the inferior rectus muscle; (b) implant a cylindrical neodymium iron boron magnet with a diameter of 3.73 mm and a thickness of 2 mm above the orbit; (c) postoperative X-rays 播散".…”