Contralateral Inferior Rectus Research Articles

Fadenoperation for the Management of Complicated Incomitant Vertical Strabismus

We reviewed retrospectively the records of 17 patients with incomitant vertical diplopia secondary to an underacting inferior rectus muscle who had been treated by surgically weakening the contralateral inferior rectus muscle with a posterior fixation suture (fadenoperation). This was the sole procedure in four patients with blowout fractures and in two patients with restriction secondary to scleral buckling procedures. It was combined with horizontal or vertical muscle surgery in 11 patients. The procedure was particularly useful in preventing diplopia on downgaze after excessive weakening of a tight inferior rectus muscle in seven patients with thyroid ophthalmopathy. In three patients it was used in anticipation of an iatrogenic incomitancy in downgaze secondary to a large recession of a tight inferior rectus muscle. All patients were markedly improved after surgery and no complications were encountered.

Masked Bilateral Superior Oblique Palsy: Clinical Features and Diagnosis

Ninety-two patients treated surgically between 1972 and 1983 were diagnosed initially as having a unilateral superior oblique palsy (SOP). On follow-up, eight (8.7%) developed findings of an SOP of the other eye. Such patients have "masked bilateral" superior oblique palsy. All eight patients had unilateral inferior oblique weakening with or without contralateral inferior rectus recession as the initial surgery. The "unmasking" of the contralateral palsy manifested in seven cases by an overaction of the contralateral inferior oblique muscle and appeared an average of 9.8 weeks (range five days to 11 months) after the first surgery. Their preoperative mean V-shift (7.6 diopters), mean excyclotorsion (5.7 degrees), and mean difference of hyperdeviation on right versus left tilt (19.6 diopters) were not significantly different from the respective values for patients with unilateral SOP (5.0 diopters, 4.3 degrees, 19.0 diopters).

Repairing the Superior Oblique Tendon-Reply

In Reply. —Dr Kopf's question highlights some difficulties involved in managing superior oblique paresis combined with restriction of upgaze in adduction. In managing both our cases, we did not wish to exacerbate the patients' poor elevation in adduction and, therefore, we did not weaken the ipsilateral inferior oblique muscle. In the first case, weakening of the ipsilateral superior rectus muscle at the initial procedure successfully diminished the vertical deviation and left the contralateral inferior rectus muscle available for a subsequent procedure. We learned from the first case that the initial procedure to free the restriction of the damaged superior oblique tendon is followed by months of gradual reduction of the restriction (aided by a functioning inferior oblique muscle) and gradual progression of the superior oblique paresis. Because of this, when faced with the second case, we did not attempt to address the vertical deviation at all during the initial procedure

Branching pattern and properties of vertical- and horizontal-related excitatory vestibuloocular neurons in the cat.

1. The axonal trajectories of excitatory vestibuloocular neurons and their synaptic contacts with extraocular motoneurons were studied by means of spike-triggered signal averaging and microstimulation techniques. A majority of the excitatory neurons related to the vertical semicircular canals were located in the border of the descending and medial nuclei and the rostral half of the descending nucleus. 2. Individual vestibuloocular neurons activated by stimulation of the ampullary nerve of the anterior semicircular canal excited motoneurons within both the contralateral inferior oblique and contralateral superior rectus motoneuron pools. 3. Individual vestibuloocular neurons receiving input from the ampullary nerve of the posterior semicircular canal excited motoneurons in both the contralateral trochlear nucleus and contralateral inferior rectus motoneuron pools. The branching pattern of single vestibuloocular neurons activated by the anterior and posterior canals probably underlies conjugate eye movement during vertical head rotation. 4. Time to peak and shape indices of unitary excitatory postsynaptic potentials (EPSPs) suggested that the location of the synaptic contact of vestibuloocular neurons was on the soma or proximal dendrites of the target extraocular motoneurons. 5. In contrast, we did not find conclusive evidence that single vestibuloocular neurons receiving input from the horizontal semicircular canal give off axon collaterals to motoneurons innervating both the contralateral lateral rectus and the ipsilateral medial rectus muscles. Projection of horizontal vestibuloocular neurons to motoneurons supplying individual muscles might be useful for convergence during horizontal head movement.

The superior oblique: a challenging extraocular muscle.

Isolated paralysis of one or both superior oblique muscles in a consecutive series of 43 patients was found to occur most often by indirect injury to the skull. The etiology in the group of spontaneous cases was mostly vascular. With rare exceptions the latter recovered spontaneously. Those with traumatic palsy may be due to "contrecoup" trauma at the decussation of the nerves or by decompensation of the cerebral fusional mechanism, with dissociation of the images of the two eyes and subsequent vertical deviation. The traumatic cases never recover spontaneously and recession or myectomy of the ipsilateral inferior oblique with or without recession of the contralateral inferior rectus is recommended but only in cases of more than 8 diopters squint, and in cases which do not adapt themselves by minor head-tilting.

Vestibulo-ocular reflex from the posterior canal nerve to extraocular motoneurons in the cat

In the anesthetized cat, the posterior canal nerve (PCN) was stimulated by electric pulses and synaptic responses were recorded intracellularly in the three antagonistic pairs of extraocular motoneurons. Pure reciprocal effects were obtained in the motoneurons innervating the antagonistic pair of ipsilateral oblique muscles and the antagonistic pair of contralateral vertical rectus muscles. These responses consisted of low threshold disynaptic excitatory postsynaptic potentials (EPSPs) in either the contralateral superior oblique (c--SO) (trochlear) or contralateral inferior rectus (c--IR) motoneurons and of disynaptic inhibitory postsynaptic potentials (IPSPs) in either the ipsilateral inferior oblique (i--IO) or ipsilateral superior rectus (i--SR) motoneurons. In addition, disynaptic IPSPs were also found in (i--SO) motoneurons. Mixtures of low threshold (di or trisynaptic) EPSPs and IPSPs were found in all other extraocular motoneurons except for the contralateral lateral rectus (c--LR) motoneurons. These results may afford a basis for the characteristic eye movements induced by vertical canal nerve stimulation.

Eye movements from single utricular nerve stimulation in the cat.

Single utricular nerves were electrically stimulated in the cat. The induced eye movements were almost pure rotation in both eyes. In addition to rotation, there were upward shifts in the ipsilateral eye and downward shifts in the contralateral eye. Slight contralateral horizontal shifts occurred in both eyes. Tension increases in extraocular muscles were strongest in the ipsilateral superior oblique and contralateral inferior oblique. They were weaker in the ipsilateral superior rectus and contralateral inferior rectus, and were weakest in the ipsilateral medial rectus and contralateral lateral rectus muscles. The tension increase in the contralateral inferior oblique and the lateral rectus was studied by changing the frequency of stimulation. The utricular-ocular reflex reacted from very low to very high frequencies, as high as 1600 cps. In comparison, the cupulo-ocular reflex arc did not respond well to high frequencies. The temporal summation in the vestibulo-ocular reflexes appeared different between...