Ipsilateral Inferior Rectus Research Articles

How Lingering Fusional Adaptation Influences the Bielschowsky Head Tilt Test in Superior Oblique Paresis.

The lack of a positive Bielschowsky head tilt test (BHTT) is commonly seen as an indicator that superior oblique paresis (SOP) is not present. This study investigated the influence of fusion on the BHTT in unilateral SOP. We analyzed vertical fusional vergence using our eye-tracking haploscope and the value of BHTT difference (BHTTD) in 11 patients who were diagnosed with congenital unilateral SOP and able to fuse. Patients used one of three different mechanisms of vertical vergence to achieve fusion. The three fusional mechanisms were associated with a significantly different BHTTD (p < 0.05). Seven of the eleven patients used vertical recti-mediated fusion and had a mean BHTTD ± SD of 21.7 ± 6.3 prism diopters (PD). Three of these patients whom we measured after a patch test for at least 30 min showed a decreased BHTTD (12.7 ± 3.8 PD). Three of the eleven patients used a mixed (oblique/rectus) fusional mechanism and had a mean BHTTD ± SD of 9.3 ± 8.6 PD. Of these patients, the one whom we measured after patching showed an increase of 11 PD in BHTTD. The remaining patient used oblique muscle-mediated fusion and had a BHTTD of only 3 PD that increased to 21 PD after patching. One explanation for this BHTT behavior in the latter patient involves lingering vergence adaptation of the "paretic" superior oblique muscle (SOM) and contralateral inferior oblique muscle, which makes these muscles more effective when activated, as is the case on ipsilateral head tilt (part of the ocular counter-roll mechanism), lessening the expected increase in hyperdeviation. Similarly, in our patients with mixed fusion, the vergence-adapted "paretic" SOM and contralateral superior rectus muscle are activated on ipsilateral and contralateral tilt, respectively, lessening the hyperdeviation in both directions. In the other seven patients, however, the vergence-adapted ipsilateral inferior rectus muscle and contralateral superior rectus muscle are activated on contralateral tilt, accentuating the BHTTD. Depending upon the specific muscles used for vertical fusion, the BHTTD is decreased or increased. The presence of a large BHTTD points to lingering or persisting fusional tonus involving the vertical rectus muscles. The lack of a positive BHTT does not rule out the diagnosis of SOP, but rather may be caused by lingering or persevering fusional tonus involving the oblique muscles. Performing the BHTT after a patch test for a minimum of 30 minutes may be necessary to reveal the BHTTD, supporting the diagnosis of SOP.

The efficacy of superior rectus recession with simultaneous inferior oblique disinsertion on superior oblique palsy with superior rectus contracture

ABSTRACTPurpose: The information about superior rectus (SR) recession in cases with SR contracture coexisting with superior oblique palsy (SOP) is very limited in previous literature. The aim of this study is to evaluate the effect of SR recession, as a combined procedure with inferior oblique (IO) disinsertion, in long-standing SOP with secondary SR contracture.Methods: The medical records of the 145 patients operated for SOP were retrospectively reviewed and 15 patients who underwent SR recession met the inclusion criteria. The mean follow-up was 50.4 months.Results: The preoperative angle of deviation was within the range of 16–35 prism dioptres (PD) with a mean of 23.0 ± 5.03 PD. In all of the cases, SR recession was performed in combination with IO disinsertion. Adult patients (12) underwent adjustable SR recession. Postoperative overcorrection developed in 3 cases (20%), and in 12 patients, the postoperative vertical deviation was within the range of 0–5 PD with a mean of 1.41 ± 1.88 PD. The overcorrected three patients underwent botulinum toxin A (BTXA) injection into the ipsilateral inferior rectus muscle. The deviation is well controlled by BTXA injection in two patients, whereas the other one was considered as masked bilateral SOP and underwent IO disinsertion in the other eye.Conclusion: Our results suggested that SR recession in combination with IO disinsertion is an effective procedure to control large vertical deviations in SOP with SR contracture in the majority of cases. However, the risk of overcorrection should be considered despite adjustable SR weakening and BTXA injection seems efficient to rescue overcorrections in long term.

Surgical Management in Type 1 Monocular Elevation Deficiency.

To evaluate the outcome of surgical treatment in patients with type 1 monocular elevation deficiency. Patients who were diagnosed as having type 1 monocular elevation deficiency by forced duction test and exaggerated traction test between 2000 and 2016 were retrospectively reviewed. Epidemiologic and clinical features of the patients were noted. The efficacy of ipsilateral inferior rectus recession to vertical misalignments and limitation of elevation were evaluated. The clinical features of the patients who did not achieve surgical success after inferior rectus recession were determined. The surgical and functional results of contralateral superior rectus recession were evaluated for patients who had residual hypotropia under inferior rectus recession. Thirty-nine patients were included in the study. Preoperatively, vertical deviations were 20.53 ± 4.50 prism diopters (PD) for near and 22.21 ± 5.12 PD for distance. After inferior rectus recession, the amount of vertical deviation corrected was 15 ± 1.14 PD for near and 17.01 ± 2.00 PD for distance. Ten (25.64%) patients did not achieve surgical success (> 6 PD residual hypotropia). Nine patients (preoperative inferior rectus recession measurements = 28.77 ± 7.25 PD for near and 27 ± 7.44 PD for distance) underwent contralateral superior rectus recession as a second surgery. After contralateral superior rectus recession, 7 of 9 (77.78%) patients achieved surgical success. The limitation of elevation significantly improved after both surgeries (Wilcoxon test, P < .05). No diplopia or other complications after surgeries were reported. Inferior rectus recession is the first surgical option for patients with type 1 monocular elevation deficiency. Contralateral superior rectus recession is an effective alternative surgical treatment for residual hypotropia after ipsilateral inferior rectus recession. [J Pediatr Ophthalmol Strabismus. 2018;55(6):369-374.].

Knapp procedure and modified Knapp procedure with Foster suture for the treatment of double elevator palsy

Objective: To investigate the efficacy of Knapp procedure and modified Knapp procedure with Foster suture in the treatment of double elevator palsy(DEP). Methods: Retrospective study. Twenty-two patients with congenital DEP were underwent Knapp procedure (n=15) and modified Knapp procedure(n=7). The clinical data were retrospectively analyzed, including the preoperative and postoperative vertical deviation in the primary position, ocular motility, and binocular vision. Results: The average vertical deviation in the primary position was (34.7±8.6) prism diopters(PD) before surgery and (6.5±6.5) PD after surgery (t=30.41, P=0.00) in the group underwent Knapp procedure. The mean preoperative and postoperative deviations of the group underwent modified procedure were respectively (38.6±14.6) PD and (5.7±9.3)PD (t=15.33, P=0.00). The mean corrected vertical deviation of the latter (32.8±5.7) PD was greater than that of the former (28.1±3.6) PD(t=-2.39, P=0.03). The mean improved upgaze in the modified group (2.6±0.5) was more obvious than that in the Knapp group (1.9±0.6) (t=2.41, P=0.02). There is no significant difference in the surgical effect on downgaze between two groups (U=43.00, P=0.54). Seven patients having binocular vision with abnormal head posture (AHP) before surgery obtained binocular single vision in the primary position and reading position after operations. AHP disappeared or reduced to less than 5°. The surgical outcomes were satisfied in 72.7% patients. But the patients with ≥40 PD preoperative vertical deviation were under-corrected and needed the further operations. Conclusions: Knapp procedure and modified Knapp procedure with Foster suture were the efficient procedures for treatment of DEP without restriction of ipsilateral inferior rectus. Both procedures can obviously correct the vertical deviation and improve upgaze without remarkable limitation of downgaze, which is good to obtain the binocular single vision in the primary and reading position. The modified procedure has more powerful effect on the corrected vertical deviation and improved upgaze. (Chin J Ophthalmol, 2017, 53: 903-907).

Levator Muscle Enlargement in Thyroid Eye Disease-Related Upper Eyelid Retraction.

To identify levator palpebrae superioris enlargement in thyroid eye disease (TED)-related upper eyelid retraction (ULR). Retrospective case-control. Subjects included 50 consecutive patients with unilateral thyroid eye disease-related ULR ≥ 2 mm and no previous eyelid surgery. The contralateral side was used as control. Clinical information was recorded from charts. CT scans were assessed by investigators blinded to the clinical data. A prediction of retracted side was made based on CT scan appearance and on basis of measured levator palpebrae superioris cross-sectional area at 2 defined points. Statistical analysis determined correlation between levator palpebrae superioris size and presence of ULR. The study was approved by the institutional ethics committee. Side with ULR predicted from CT scan review in over 85% of cases. Mean cross-sectional area of levator palpebrae superioris on retracted side was significantly larger than nonretracted side at 2 separate sites. Levator palpebrae superioris area was larger on retracted side compared with nonretracted side in over 85% of subjects. More than 30% of subjects had no enlargement of other extraocular muscles. Only 6% of patients had enlargement of the ipsilateral inferior rectus muscle. Levator palpebrae superioris enlargement from inflammation or scar is a factor in thyroid eye disease-related ULR. Upper eyelid retraction can be predicted from CT scan appearance in over 85% of cases. Ipsilateral inferior rectus enlargement is rare. Levator palpebrae superioris is the most commonly targeted muscle in thyroid eye disease.

Surgical management of monocular elevation deficiency combined with inferior rectus restriction.

To evaluate the results of ipsilateral inferior rectus (IR) recession, when performed alone or in combination with contralateral superior rectus (SR) recession in patients with monocular elevation deficiency (MED) and IR tightness. The medical records of patients with MED and tight IR muscle were retrospectively reviewed. Patients underwent either ipsilateral IR recession alone (IR group) or combined with contralateral SR recession (IR+SR group). Pre- and postoperative ocular motility and alignment and fundus torsion were analyzed. Abnormal head posture was recorded. All patients were followed for at least 6 months. A total of 23 patients were identified. Mean patient age at time of surgery was 9.8 ± 8.7 years (range, 3-45 years). Ten patients underwnet ipsilateral IR recession 5-8 mm; 13 patients, 4 mm ipsilateral IR recession combined with 5-12 mm contralateral SR recession. Both groups experienced marked improvement in ocular alignment in the primary position (P = 0.34). However, there was a statistically better ocular alignment in both upgaze (P=0.03) and downgaze (P < 0.01) in the IR+SR group, with a lower degree of fundus intorsion (P < 0.01). An ipsilateral head tilt developed in 70% of patients in the IR group and in 54% of patients in the IR+SR group. In this patient cohort, combined contralateral SR recession with ipsilateral IR recession reduced postoperative IR underaction and achieved better ocular alignment in upgaze and downgaze.

Extraocular muscle injury during endoscopic sinus surgery: a series of 10 cases at a single center.

Extraocular muscle (EOM) injury is a rare but serious complication of endoscopic sinus surgery (ESS). The aim of this study is to describe the clinical characteristics and course of EOM injury occurring during ESS. Retrospective case series. Medical records and CT images of patients who suffered from EOM injury after ESS between 2006 and 2012 were retrospectively reviewed. Patient demographics, endoscopic anatomy, type of surgery (primary or revision), predisposing risk factors, site and extent of injury on CT imaging, and associated complications were evaluated. In addition, data regarding ophthalmologic management and clinical outcomes were collected. Ten patients with EOM injuries after ESS were included in this study. One patient was undergoing revision ESS. All patients sustained medial rectus muscle injury and one patient suffered concurrent ipsilateral inferior rectus muscle injury. A microdebrider was used in nine cases. Right-sided injury (90% of patients) was more prevalent than left-sided injury, and 70% of injured medial rectus muscles were completely transected. After subsequent strabismus surgery, 8/9 patients regained binocular single vision in primary gaze despite residual diplopia in some gaze positions. Although proper ophthalmologic surgery after EOM injury may improve deviation in the primary gaze position, none of the patients regained normal EOM movement. Therefore, prevention of this complication through adequate surgical technique and precautions is important.

Surgical management of long-standing antielevation syndrome after unilateral anterior transposition of the inferior oblique muscle

To investigate surgical management of patients with long-standing antielevation syndrome following unilateral anterior transposition of inferior oblique muscle. We present a series of 3 consecutive patients with significant hypotropia several years after unilateral anterior transposition surgery. An approach combining denervation-extirpation of the inferior oblique muscle and subsequent inferior rectus muscle recession and contralateral superior rectus muscle recession was used to manage all 3 patients. Denervation-extirpation surgery alone or with ipsilateral inferior rectus muscle recession were not enough to improve vertical misalignment in these patients. All 3 patients achieved successful results after denervation-extirpation surgery, ipsilateral inferior rectus muscle recession, and contralateral superior rectus muscle recession. In this case series, devervation-extirpation surgery on the inferior oblique muscle, ipsilateral inferior rectus recession, and contralateral superior rectus recession improved vertical misalignment in patients with long-standing antielevation syndrome after unilateral anterior transposition of the inferior oblique.

Extraocular muscle injury during endoscopic sinus surgery: A series of 10 cases at a single center

Extraocular muscle (EOM) injury is a rare but serious complication of endoscopic sinus surgery (ESS). The aim of this study is to describe the clinical characteristics and course of EOM injury occurring during ESS. Retrospective case series. Medical records and CT images of patients who suffered from EOM injury after ESS between 2006 and 2012 were retrospectively reviewed. Patient demographics, endoscopic anatomy, type of surgery (primary or revision), predisposing risk factors, site and extent of injury on CT imaging, and associated complications were evaluated. In addition, data regarding ophthalmologic management and clinical outcomes were collected. Ten patients with EOM injuries after ESS were included in this study. One patient was undergoing revision ESS. All patients sustained medial rectus muscle injury and one patient suffered concurrent ipsilateral inferior rectus muscle injury. A microdebrider was used in nine cases. Right-sided injury (90% of patients) was more prevalent than left-sided injury, and 70% of injured medial rectus muscles were completely transected. After subsequent strabismus surgery, 8/9 patients regained binocular single vision in primary gaze despite residual diplopia in some gaze positions. Although proper ophthalmologic surgery after EOM injury may improve deviation in the primary gaze position, none of the patients regained normal EOM movement. Therefore, prevention of this complication through adequate surgical technique and precautions is important.

New strabismus surgical techniques

Five new strabismus surgical procedures were developed by the authors and were presented as a workshop at the AAPOS annual meeting of the American Association for Pediatric Ophthalmology and Strabismus. They are summarized here to introduce these methods to the reader and provide surgeons with more options in approaching difficult strabismus problems. Diagnosis and correction of consecutive strabismus attributable to stretched scar is discussed. The pulley posterior fixation procedure is a unique approach to correct high accommodative convergence or to augment a maximal medial rectus recession. Diagnosis and repair of the partial avulsion (flap tear) of a rectus muscle allows correction of some restrictive strabismus following blunt trauma. The nasal myectomy of the inferior oblique muscle corrects persistent inferior oblique overaction without sacrificing the tether effect gained by a previous anterior transposition of the inferior oblique. The full advancement of the superior oblique tendon offers another option to strengthen a weak superior oblique muscle.

Partial third cranial nerve palsy: clinical characteristics and surgical management

PurposeIncomplete recovery from injury to the third cranial nerve results in ocular misalignment and associated diplopia. Our aim in this study was to describe and evaluate strabismus surgery strategies aimed at restoring functional, single binocular vision in this population. DesignRetrospective review. ParticipantsWe studied 12 adult patients with acquired partial third cranial nerve palsy who underwent strabismus surgery. MethodsThe 12 consecutive patients with residual third nerve palsy were selected from among the patients seen between 2000 and 2010 in the clinical practice of 1 strabismologist (M.F.). Complete pre- and postoperative ophthalmologic and orthoptic examinations were performed in each patient. The patients presented with isolated hypotropias (n = 7) and exohypotropias (n = 5). Strabismus surgery included: contralateral superior rectus recession, ipsilateral inferior rectus recession, vertical transposition of horizontal recti, horizontal rectus muscle surgery, or combined horizontal and vertical muscle surgery. Complete surgical success was defined as postoperative alignment within 5 prism diopters (PD) of orthotropia and the absence of diplopia in functional positions of gaze. The average follow-up was 23 months (range, 7 to 81 months). ResultsThe mean preoperative vertical and horizontal deviations were 19 PD hypotropia (8–40 PD) and 19 PD exotropia (6–40 PD), respectively. The mean postoperative deviations were 2 PD hypotropia (0–8 PD) and 1 PD exotropia (0–6 PD). Complete surgical success was achieved in 7 of 12 patients. Partial success was attained in 5 of 12 patients, who experienced significant improvement but required postoperative use of a prism. ConclusionsThis study indicates that patients with incomplete third cranial nerve paralysis may enjoy good functional and cosmetic outcomes with strabismus surgery.

Vertical Rectus Surgery for Knapp Class II Superior Oblique Muscle Paresis

To evaluate the efficacy of treating Knapp class II superior oblique muscle palsy with 7-mm nasal transposition of the ipsilateral inferior rectus muscle combined with recession of the contralateral inferior rectus muscle when the primary position hypertropia is 10 prism diopters (PD) or less. A retrospective review of 8 consecutive patients with superior oblique muscle paresis who had nasal transposition of the inferior rectus muscle in the paretic eye and recession of the inferior rectus muscle in the nonparetic eye. Ocular motility, including objective and subjective torsion, were evaluated before and after surgery. The mean (SD) preoperative hypertropia was 5 PD (1.5) and 13.1 (3.6) PD in the primary position and downgaze, respectively. After surgery the mean (SD) hypertropia was 1.25 (1.0) and 3.25 (1.3) PD in the primary position and downgaze, respectively. The mean (SD) subjective excyclotropia decreased from 6.6 degrees (1.3 degrees) preoperatively to 0.5 degrees (0.9 degrees) after surgery, and there was a mean (SD) objective decrease in the excyclotorsion of the paretic eye by 7.8 degrees (1.4 degrees). All patients were diplopic before surgery and asymptomatic after surgery. Treatment with 7-mm nasal transposition of the ipsilateral inferior rectus muscle combined with recession of the contralateral inferior rectus muscle can effectively treat Knapp class II superior oblique muscle palsy when the primary position hypertropia is 10 PD or less.

Treatment of Knapp Class V superior oblique palsy with contralateral inferior rectus muscle recession

Objective: To describe the clinical features of patients with Knapp Class V superior oblique palsy (hypertropia greatest across the lower fields of gaze) and to present the results of a contralateral, adjustable, inferior rectus muscle recession procedure performed on these patients. Design: Clinical, cohort study. Participants: We retrospectively reviewed a series of 4 cases of superior oblique palsy (Knapp Class V). The patients, seen between the years 1991 and 2000, were selected from the private practice of 1 of the authors (Michael Flanders). Methods: Clinical and surgical data were extracted from the patients' records. All patients had had complete ophthalmologic and orthoptic assessments. Those included in this series had difficulty reading and compensated by lowering their chins. They had a hypertropia, which increased in downgaze, decreased in upgaze, and increased on ipsilateral head tilt. Both the ipsilateral superior oblique and inferior rectus muscles were underactive. All 4 patients underwent contralateral, adjustable, inferior rectus muscle recession. Results: The mean vertical deviation of the paretic eye preoperatively was 8.25 prism D (PD) in primary position and 20 PD in downgaze. Postoperatively it was 2 PD in primary position and 5 PD in downgaze. All patients had improved head posture and a more comfortable reading position after surgery. Mean follow-up was 6.4 years (range 1–9 years). Conclusions: Contralateral inferior rectus muscle recession is an effective treatment for visual symptoms associated with Knapp Class V superior oblique palsy.

Correction of cyclovertical strabismus induced by limited macular translocation in a case of age-related macular degeneration

PURPOSE: To report a case of strabismus surgery performed to treat cyclovertical strabismus induced by limited macular translocation. METHODS: Case report. RESULTS: A 62-year-old man suffering with age-related macular degeneration and subfoveal choroidal neovascularization, RE, underwent limited macular translocation surgery. The fovea was rotated downward, and his visual acuity improved from 20/100 to 20/25 postoperatively. Cyclovertical diplopia persisted for 6 months after the operation. A Hess screen test revealed a pattern that simulated an underaction of the superior oblique muscle and inferior rectus muscle with an overaction of the ipsilateral inferior oblique muscle. To treat the diplopia, advancement of the superior oblique muscle tendon and resection of the ipsilateral inferior rectus muscle were performed. Binocular single vision with 140 seconds of arc for stereopsis was obtained. CONCLUSION: Cyclovertical strabismus after limited macular translocation is corrective with conventional surgery on the treated eye.

Bilateral inferior rectus muscle recession for correction of hypotropia in dysthyroid ophthalmopathy

Purpose: The restrictive myopathy of dysthyroid ophthalmopathy frequently results in strabismus and diplopia. The most common deviation is hypotropia. Ipsilateral inferior rectus muscle recession, the generally accepted treatment, may lead to a progressive marked overcorrection. The purpose of this study is to evaluate the results of bilateral asymmetric inferior rectus muscle operations with regard to late progressive overcorrection. Methods: A retrospective review of all patients undergoing bilateral inferior rectus muscle recession for dysthyroid ophthalmopathy between 1993 and 1997 found 8 patients with hypotropia resulting from dysthyroid ophthalmopathy. Alignment and motility were assessed preoperatively and postoperatively in all patients. Bilateral asymmetric inferior rectus muscle recession was performed on all patients with an adjustable suture performed on the hypotropic eye. A successful, long-term, postoperative result was defined as orthophoria or a vertical misalignment of less than or equal to 5 PD in primary gaze. Results: Data were collected from 8 patients at 4 to 6 weeks postoperatively. Six patients had successful alignment, and 2 patients remained undercorrected. Seven patients were successfully aligned, and 1 patient was undercorrected at the latest postoperative examination (mean, 18 months). Conclusion: In our series, bilateral asymmetric inferior rectus muscle recession resulted in successful correction of hypotropia without late postoperative overcorrections in patients with dysthyroid ophthalmopathy. (J AAPOS 1999;3:157-9)

Are laws that govern behavior embedded in the structure of the CNS? The case of Hering's law

The pattern of axonal terminations of individual premotoneuronal medium lead burst neurons (MLBs) has been elucidated with the help of the intraaxonal recording and horseradish peroxidase injection technique in alert behaving monkeys. These findings indicate that individual MLBs do not influence individual muscles; instead they influence groups of muscles. Horizontal medium lead burst neurons (EBNs) project to ipsilateral lateral rectus motoneurons directly, and could contact contralateral medial rectus motoneurons indirectly, through the internuclear neurons of the ipsilateral abducens nucleus. Also, upward MLBs project to motoneurons innervating both the superior rectus and the inferior oblique muscles of both eyes. Finally, downward MLBs project to ipsilateral motoneurons innervating the ipsilateral inferior rectus muscle and the contralateral superior oblique muscle. All in all, the pattern of oculomotor terminations of MLBs provides experimental support for Hering's law of equal innervation. EBNs also project to the nucleus prepositus hypoglossi while vertical MLBs also project to the interstitial nucleus of Cajal (NIC). These structures are thought to participate in the process of “velocity to position integration”, in the horizontal and vertical planes respectively. Intracellular recording from individual neurons of the NIC in alert behaving monkeys followed by biocytin or horseradish peroxidase injections demonstrates that their axons pass through the posterior commissure on their way to vertical extraocular motoneurons. It also demonstrates that these fibers carry a phasic signal related to saccades and a tonic signal related to eye position in a precise quantitative manner. Work is in progress to determine whether their pattern of oculomotor terminations is also appropriate for Hering's law.

Treatment of residual dissociated vertical deviation with inferior rectus resection.

The effectiveness of an ipsilateral 4-millimeter resection of the inferior rectus muscle was evaluated as a treatment of recurrent dissociated vertical deviation. Thirty-six patients who had an unsatisfactory outcome after 7- to 9-millimeter recession of the superior rectus muscle had an ipsilateral inferior rectus muscle resection. The dissociated vertical deviation was fully corrected in 18 patients and improved in 15 patients. Only three patients (8%) had an unsatisfactory result. Multivariate analysis of four preoperative features including the amplitude of the dissociated deviation, the age at diagnosis, the age at surgery, and the degree of amblyopia failed to define any factors that could predict surgical success.

Inferior Rectus Muscle Contracture Syndrome after Retrobulbar Anesthesia

Ipsilateral hypotropia with restricted elevation is an increasingly recognized strabismic entity resulting from injury to the inferior rectus muscle after local retrobulbar anesthesia. Eight patients with this disorder are described. Computed tomography of the orbit in three patients demonstrated isolated segmental enlargement of the retrobulbar portion of the inferior rectus muscle; the findings of magnetic resonance imaging in one patient was most compatible with fibrosis. Four patients underwent strabismus surgery consisting of adjustable recession of the affected inferior rectus muscle; all recovered single binocular vision in the functional fields of gaze postoperatively. Surgical exploration of the ipsilateral inferior rectus muscle demonstrated normal anatomy in the peribulbar portion of the muscle.

A note on the development of the vestibulo-ocular pathway in the chicken

The vestibulo-ocular pathways have been examined in embryonic chicks using horseradish peroxidase or diI as retrograde and anterograde tracers. The vestibular neurons project to the rostral, external eye motor nuclei over one or the other of three separate pathways; the ipsilateral and contralateral medial longitudinal fascicle and the contralateral brachium conjunctivum. The brachium conjunctivum component originates dorsally in the superior vestibular region and projects to the contralateral inferior oblique and superior rectus motor nuclei. An ipsilateral component of the medial longitudinal fascicle is labeled from more ventral sites in the vestibulo-cerebellar process and terminates in the ipsilateral superior oblique and inferior rectus nuclei. The contralateral medial longitudinal fascicle component originates still more ventrally and terminates in the contralateral superior oblique and inferior rectus motor nuclei. Accordingly, the vestibulo-ocular pathways in chickens operate predominantly on synergistic pairs of external eye muscles. These selective terminal fields are established within a day or two after the first terminals invade the eye motor nuclei during embryogenesis.

Structure of the primate oculomotor burst generator. I. Medium-lead burst neurons with upward on-directions

1. To investigate the structure of the primate burst generator for vertical saccades, we obtained intra-axonal records from vertical medium-lead burst neurons with upward on-directions (UMLBs) in alert, behaving squirrel monkeys, while monitoring their spontaneous eye movements. After physiological characterization, these UMLBs were injected with horseradish peroxidase. 2. UMLBs (n = 14) had no spontaneous activity and emitted bursts of action potentials that preceded rapid eye movements by approximately 6 ms. Parameters of the burst (duration and number of spikes) were highly correlated with parameters of the rapid eye movement (duration and amplitude of the upward displacement of the eyes). 3. The axons of six UMLBs projected to the oculomotor complex. Their somata (4 were recovered) were all in the rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF). Their axons traveled caudally in the medial longitudinal fasciculus (MLF) and ramified in the interstitial nucleus of Cajal (NIC) before entering the oculomotor nucleus. Five axons terminated bilaterally in the subdivisions innervating the superior rectus and inferior oblique muscles and therefore were presumed to be excitatory. One axon terminated in the ipsilateral inferior rectus and superior oblique subdivisions of the oculomotor complex and was presumed to be inhibitory. 4. Additionally, our data demonstrate that the nucleus of the posterior commissure (nPC) may also contain UMLBs. The axon of one such neuron crossed the midline within the posterior commissure and provided terminal fields to the contralateral nPC, riMLF, NIC, and the mesencephalic reticular formation but not to the oculomotor complex. 5. In conclusion, our data demonstrate that the rostral mesencephalon of the monkey contains neurons that have both the activity and the connections that are necessary either to provide motoneurons innervating extraocular muscles of both eyes with the pulse of activity they display during upward saccades or to inhibit their antagonists. Furthermore, our data demonstrate that some UMLBs are better suited for closing the feedback path of the local feedback loop rather than for providing direct input to extraocular motoneurons.