| PURPOSE. To investigate the electronystagmograph waveform after bilateral medial rectus recession and bilateral lateral rectus tenotomy in one subject with infantile nystagmus syndrome (INS) and esotropia and amblyopia and ocularcutaneous albinism (OCA).
METHODS During his preoperative and postoperative visits to the clinic, binocular recordings of the eye movements of the subject were undertaken using an infrared reflection tracking system (IOTA Orbit Eye Trace). The subject viewed the target binocularly and monocularly in different gaze and convergence.
RESULTS The patient was 55 y/o when he first came to the clinic. He has a history of nystagmus since his infancy. Ophthalmic examinations showed that he had INS and 52Δ ET and OCA and OND and amblyopia. Clinical investigation also identified that the patient had constant, symmetric, conjugate, moderate amplitude, moderate frequency horizontal, jerk involuntary ocular oscillations. There was a consistent and prominent left head/face turn with a clinical null position/neutral position about 20-25 degrees of right gaze. Preoperative eye movement recordings (EMR) showed constant, symmetric involuntary oscillations, which varied, from 2-4 HZ with jerk fast phases and increasing/linear velocity slow phase waveforms. Convergence dampening was not obvious. The fast phase direction of his nystagmus changed from jerk to left with left eye viewing to jerk to right with right eye viewing –latent components. The fast phase direction did not change during the 5 minute recording. Adduction of each eye showed less intense nystagmus. Both eyes had good foveation periods. The patient received the operation of bilateral medial rectus recession of 5mm and bilateral lateral rectus tenotomy. At 2 months after surgery, the EMR still showed constant, symmetric involuntary oscillations, which varied, from 2-4 HZ with jerk fast phases and increasing/linear velocity slow phase waveforms, while the convergence dampening was very clear – there were almost no oscillations during near viewing. His nystagmus became less intense right around primary position.
CONCLUSIONS This patient had ET and amblyopia, therefore his binocular vision is poor. Usually, this situation is not the indication for artificial divergence surgery due to the general opinion that the convergence dampening doesn’t work without binocular fusion. We found that this patient demonstrated obvious improvement of nystagmus after bilateral medial rectus recession and bilateral lateral rectus tenotomy. This result implied that the convergence perhaps does not depend on the neural control of binocular perception. We suggested that the monocular fixation of the dominant eye play an important role in binocular fixation. The binocular motion fusion depends on both the fixation ability of the dominant eye and the dynamic balance between the antagonist muscles of either eye. We considered that as far as this patient was concerned, not only the procedure of rectus tenotomy improved the foveation of nystagmus, but also the bilateral medial rectus recession increased the impulse threshold for the medial rectus to keep fixation and the dynamic balance between medial and lateral rectus, and this increased tension that may be sensed by EOM proprioceptors is further transferred to the neural center in which in turn the feedback signal is output to the EOM so that the nystagmus is dampened. |
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