Abstract
Abstract: :
Purpose: The four–muscle tenotomy procedure was developed to damp Infantile Nystagmus Syndrome (INS)—fka Congenital Nystagmus (CN)—and was hypothesized to improve other forms, including acquired nystagmus. We wished to investigate the effects of this procedure on the acquired pendular nystagmus waveforms of a subject with multiple sclerosis (MS) and intractable oscillopsia Methods: Both medial recti were tenotomized in addition to recessing the lateral recti to correct an exotropia. Horizontal, vertical, and torsional pre– and post–tenotomy ocular motility recordings were made using the search–coil technique; data were sampled at 500 Hz. Fixation (monocular and binocular), saccades, pursuit and the OKR and VOR were tested. Horizontal data were analyzed for instantaneous peak–to–peak velocities of the nystagmus, and average amplitude and frequency of the nystagmus. Results: The subject’s post–tenotomy, peak–to–peak slow–phase velocities decreased by 38–77.5% (avg = 50%) in the right eye and 50% in the left eye. The nystagmus amplitudes also decreased by 50% and the frequencies remained unchanged at 3.7 Hz. Visual acuity increased from 0.125 OU pre–op to 0.2 OD and 0.25 OS post–op, or 60% and 100% respectively. As expected, the patient’s voluntary saccades and abducting saccadic pulses, secondary to his bilateral INO, were unaffected. Conclusions: The four–muscle tenotomy procedure developed on a canine model of INS and demonstrated to be successful in a masked clinical trial was also effective in reducing acquired pendular nystagmus secondary to MS and thereby reducing oscillopsia. This is consistent with the hypothetical mode of action of tenotomy, i.e., a reduction of the small–signal gain of the ocular motor plant secondary to interference with a proprioceptive tension–control loop. Therefore, in addition to damping IN, tenotomy should damp other acquired pendular instabilities; its effectiveness on acquired jerk nystagmus (e.g., vestibular or gaze–evoked) is yet to be demonstrated.
Keywords: nystagmus • strabismus: treatment • ocular motor control