Is the central mesencephalic reticular formation a purely horizontal gaze center?

Historically, the central mesencephalic reticular formation has been regarded as a purely horizontal gaze center based on the fact that electrical stimulation of this region produces horizontal saccades, it provides monosynaptic input to medial rectus motoneurons, and cells recorded in this region often display a peak in firing when horizontal saccades are made. We tested the proposition that the central mesencephalic reticular formation is purely a horizontal gaze center by examining whether this region also supplies terminals to superior rectus and levator palpebrae superioris motoneurons, both of which fire when making vertical eye movements. The experiments were carried out using dual tracer techniques at the light and electron microscopic level in macaque monkeys. Injections of biotinylated dextran amine or Phaseolus vulgaris leukoagglutinin into the central mesencephalic reticular formation produced anterogradely labeled terminals that were in synaptic contact with superior rectus and levator palpebrae superioris motoneurons that had been retrogradely labeled. These results indicate that this region is not purely connected with horizontal gaze motoneurons. In addition, we found that the number of contacts on vertical gaze motoneurons increased with more rostral injections involving the mesencephalic reticular formation adjacent to the interstitial nucleus of Cajal. This suggests that there is a caudal to rostral gradient for horizontal to vertical saccades, respectively, represented within the midbrain reticular formation. Finally, we utilized post-embedding immunohistochemistry to show that a portion of the labeled terminals were GABAergic, indicating they likely originate from downgaze premotor neurons.

How Much Superior Rectus Underaction is Considered Normal?

Purpose:

It is considered normal to have a small amount of superior rectus weakness in laevo and dextro elevation; however, there is no documented definition for these normal parameters within a healthy young adult population using ocular movement testing and the synoptophore. The aim of this study was to collect normative data on the degree of superior rectus underaction in healthy young adults.

Method:

Twenty-nine healthy adults (3 males and 26 females, mean age 20.30 ± 1.70 years) were recruited. Superior recti underactions and inferior oblique overactions were recorded during routine ocular movement testing and mean and median values calculated. Subjective horizontal, vertical and torsional measurements were taken in degrees on the synoptophore in primary position, laevo elevation and dextro elevation.

Results:

Most participants (79.31%) had some degree of observable superior rectus underaction in either eye or in both eyes on ocular movement testing (mean superior rectus underaction of –0.69 units in laevo elevation and –0.71 units in dextro elevation, range = –1.5 to –0.5 units; median –1 units, interquartile range (IQR) = –1 to –1 units). Most participants (62.07%) had some degree of superior rectus underaction in either eye or in both eyes on the synoptophore (mean left and right superior recti underactions of –0.48 degrees, range = –3 to –1 degrees; median 0 degrees, IQR = –1 to –1 degrees).

Conclusion:

The majority of young healthy adults in this study showed some degree of superior rectus underaction. On ocular movement testing, –0.70 units of underaction, and on the synoptophore, –0.48 degrees of underaction are the mean levels of weakness to be expected. Superior rectus underactions greater than –1 units for ocular movement testing and –1 degrees on the synoptophore in healthy young adults should be carefully evaluated, together with other important clinical signs.

Superior rectus muscle insertion injury following cosmetic upper lid blepharoplasty: a case report

Background

Direct damage to the superior rectus (SR) muscle insertion following upper lid blepharoplasty has not been reported. We document a rare case of vertical diplopia due to direct damage to the SR muscle insertion following cosmetic upper lid blepharoplasty.

Case presentation

We describe a case of 24-year-old woman with Asian eyelid. The patient had already undergone multiple cosmetic upper lid surgeries and complained of vertical diplopia immediately after her most recent surgery (levator resection with skin approach). Preoperatively, large-angle right hypotropia and severe upgaze limitation were present and noticeable ptosis was observed in the right eye. Intraoperatively, the SR muscle fibers were observed to be detached at the insertion site and severe fibrosis and adhesion surrounding the muscle was noted. After strabismus surgery, vertical strabismus was improved.

Conclusions

This case can provide valuable insight to surgeons performing ptosis surgery and blepharoplasty, particularly in cases of reoperation. Surgeons should be careful while manipulating the levator muscle or resecting deep tissues not to affect the SR muscle.

Waldenstrom macroglobulinemia involving the superior rectus muscle

PURPOSE

We present the first reported case of Waldenstrom macroglobulinemia in the right superior rectus causing diplopia.

OBSERVATIONS

A 72-year-old man with a 6-month history of untreated asymptomatic Waldenstrom macroglobulinemia presented with 2 years of diagonal binocular diplopia that was previously thought to be due to ocular myasthenia gravis. Examination showed mild right proptosis and right hypotropia, and MRI revealed a focal lesion of the right superior rectus muscle. Orbital biopsy was performed, and histopathology showed lymphoplasmacytic infiltration among the skeletal muscle fibers of the rectus muscle. Immunostaining confirmed a B-cell preponderance, along with more extensive staining for IgM than IgG, and in situ hybridization confirmed lambda restriction. These findings corresponded with those of his previous bone marrow biopsy, confirming Waldenstrom macroglobulinemia as the etiology for the extraocular muscle mass.

CONCLUSIONS AND IMPORTANCE

Lymphoma of an extraocular muscle is a rare manifestation of orbital lymphoma, and the tumors are usually mucosa-associated lymphoid tissue (MALT) lymphomas (i.e. extranodal marginal zone lymphomas). There are 4 previous reports of lymphoplasmacytic lymphoma of an extraocular muscle; however this is the first reported case of such a lesion in a patient with concurrent Waldenstrom macroglobulinemia at the time of diagnosis.

A novel case of superior rectus injury and its subsequent surgery

We report a presumed damage to the left superior rectus (SR) muscle following a dog bite injury that resulted in a marked weakness of elevation and vertical diplopia. A 30-year-old male presented in October 2010 following a dog bite around his left superotemporal orbit. An ophthalmic examination was unremarkable. The patient immediately complained of vertical diplopia, which did not settle during a period of observation lasting approximately 9 months following the attack. An orthoptist examination confirmed a marked restriction of upgaze. A diagnosis of isolated SR injury, secondary to the dog bite, was suspected. A left Knapp procedure was performed. The surgery was uneventful with scar tissue found around the SR. Three months following his surgery, the patient was orthophoric in both primary positions and in the downgaze with a residual 20-prism dioptre hypotropia in the upgaze. Our patient was unusual in that the bite weakened the SR in isolation. We also show the successful management of this novel case using a simple Knapp procedure.

Superior rectus muscle recession for residual head tilt after inferior oblique muscle weakening in superior oblique palsy

Purpose

Residual head tilt has been reported in patients with superior oblique muscle palsy (SOP) after surgery to weaken the inferior oblique (IO) muscle. The treatments for these patients have not received appropriate attention. In this study, we evaluated the superior rectus (SR) muscle recession as a surgical treatment.

Methods

The medical records of 12 patients with SOP were retrospectively reviewed. Each of these patients had unilateral SR muscle recession for residual head tilt after IO muscle weakening due to SOP. The residual torticollis was classified into three groups on the basis of severity: mild, moderate, or severe. Both IO muscle overaction and vertical deviation, features of SOP, were evaluated in all patients. The severity of the preoperative and postoperative torticollis and vertical deviation were compared using a paired t-test and Fisher's exact test.

Results

The torticollis improved in nine of 12 (75%) patients after SR muscle recession. The difference between the preoperative and postoperative severity of torticollis was statistically significant (p = 0.0008). After surgery, the mean vertical deviation was significantly reduced from 12.4 prism diopters to 1.3 prism diopters (p = 0.0003).

Conclusions

Unilateral SR muscle recession is an effective method to correct residual head tilt after IO muscle weakening in patients with SOP. This surgical procedure is believed to decrease head tilt by reducing the vertical deviation and thereby the compensatory head tilt.

A cadaveric anatomical study of the levator aponeurosis and Whitnall's ligament

PURPOSE

To identify the anatomy of the levator aponeurosis (LA) and Whitnall's ligament (WL) in Korean subjects using cadavers.

METHODS

Orbital exenteration was performed in ten cadavers (20 eyeballs) that had no history of trauma near the eyeball. We observed characteristics of WL (tension, density, and shape) and the relationship between the superior rectus muscle (SR) and the levator palpebrae superioris. We measured the distance from both the eyelid margin and the upper border of the tarsal plate to the insertion of the LA medially, centrally, and laterally.

RESULTS

The WLs we observed showed several shapes. In 12 eyes, we saw clear, white fibrotic bands, while in four others, we found thin, less taut bands. In four eyes, we were unable to identify the precise shape of the band. The insertions of the LA showed nasal dehiscence in 13 eyes and parallel attachment in seven eyes. The distances from the eyelid margin to the insertion of the LA medially, centrally, and laterally were 8.31 mm, 5.57 mm, and 5.15 mm, respectively. The distances from the upper border of the tarsal plate to the insertion of the LA medially, centrally, and laterally were 2.75 mm, 4.82 mm, and 4.29 mm, respectively.

CONCLUSIONS

This study examined the anatomy of WL and the LA in Korean subjects and may be helpful as a reference in levator muscle surgery.