Unveiling the vulnerability of the human abducens nerve: insights from comparative cranial base anatomy in mammals and primates.

The topographic anatomy of the abducens nerve has been the subject of research for more than 150 years. Although its vulnerability was initially attributed to its length, this hypothesis has largely lost prominence. Instead, attention has shifted toward its intricate anatomical relations along the cranial base. Contrary to the extensive anatomical and neurosurgical literature on abducens nerve anatomy in humans, its complex anatomy in other species has received less emphasis. The main question addressed here is why the human abducens nerve is predisposed to injury. Specifically, we aim to perform a comparative analysis of the basicranial pathway of the abducens nerve in mammals and primates. Our hypothesis links its vulnerability to cranial base flexion, particularly around the sphenooccipital synchondrosis. We examined the abducens nerve pathway in various mammals, including primates, humans (N = 40; 60% males; 40% females), and human fetuses (N = 5; 60% males; 40% females). The findings are presented at both the macroscopic and histological levels. To associate our findings with basicranial flexion, we measured the cranial base angles in the species included in this study and compared them to data in the available literature. Our findings show that the primitive state of the abducens nerve pathway follows a nearly flat (unflexed) cranial base from the pontomedullary sulcus to the superior orbital fissure. Only the gulfar segment, where the nerve passes through Dorello's canal, demonstrates some degree of variation. We present evidence indicating that the derived state of the abducens pathway, which is most pronounced in humans from an early stage of development, is characterized by following the significantly more flexed basicranium. Overall, the present study elucidates the evolutionary basis for the vulnerability of the abducens nerve, especially within its gulfar and cavernous segments, which are situated at the main synchondroses between the anterior, middle, and posterior cranial fossae-a unique anatomical relation exclusive to the abducens nerve. The principal differences between the pathways of this nerve and those of other cranial nerves are discussed. The findings suggest that the highly flexed human cranial base plays a pivotal role in the intricate anatomical relations and resulting vulnerability of the abducens nerve.

Inferior displacement of the lateral rectus muscle insertion in exotropia with mild V-pattern or vertical deviation.

BACKGROUND: To describe clinical features and intraoperative findings of the patients with exotropia who presented mild V-pattern or vertical deviation, and to investigate the surgical outcomes of anatomical relocation of inferiorly displaced lateral rectus (LR) muscle insertion. METHODS: Detailed ophthalmological evaluations were obtained in 42 consecutive patients, and the horizontal rectus muscle insertions were detected intraoperatively. The displaced insertion of LR muscle was corrected accompanied with classic recession-resection procedure. RESULTS: The inferiorly displaced LR muscle insertions were detected in 19 patients (Group A), while the remaining 23 patients (Group B) had normal insertions. The mean distance of displaced insertion from the normal position was 2.92 ± 1.05 mm (range: 1.0-4.0). Mild V-pattern was more common in Group A (78.9%, 15/19) than Group B (47.8%, 11/23), and the magnitude of V-pattern in Group A (6.16 ± 3.91 PD) was also greater than Group B (3.43 ± 3.92 PD). The fundus extorsions of the affected eyes (9.68 ± 4.77 °) were greater than the contralateral eyes (5.91 ± 5.82 °) in Group A. At the 2 months follow-up, mild V-pattern and mild vertical deviation were corrected by upward transposition. The significant correlations were identified between the pre-operative misalignments and the amounts of misalignments correction. CONCLUSIONS: Nearly half of the cases with mild V-pattern or vertical deviation resulted from the inferiorly displaced LR muscle insertion, so the intraoperative exploration of the LR muscle insertion is strongly suggested. Upward transposition may effectively correct both the mild V-pattern and vertical deviation.

How to Better Treat Patients with Intermittent Exotropia: A Review of Surgical Treatment of Intermittent Exotropia.

Intermittent exotropia (X(T)) is the most common form of strabismus, especially in Asians. Treatment of X(T) includes occlusion, overminus lens, and surgery, of which, surgery is the mainstay of treatment. Commonly performed surgical procedures for X(T) are bilateral lateral rectus muscle recession or unilateral lateral rectus recession with medial rectus resection; however, it is unclear which of the two surgeries is more effective. The purpose of this review is to provide an insight on the surgical treatment of X(T). Randomized controlled trials, comparative observational studies, and case series with a large number of patients as well as a long follow-up period of over a year were included.

Lateral rectus muscle palsy secondary to sphenoid sinusitis.

Isolated sphenoid sinus disease is a rare, often misdiagnosed condition of the paranasal sinus. If left untreated, it can lead to complications involving pituitary gland, cavernous sinus, neurological and vascular structures nearby. Early recognition and treatment are critical to prevent the progression of the disease. We present a case of a 60-year-old woman with a history of severe left-sided headache, facial pain, diplopia and left lateral rectus palsy. She was initially referred to ophthalmology and rheumatology for possible giant cell arteritis. Magnetic resonance imaging revealed opacification in left sphenoid sinus with cavernous sinus/superior orbital fissure involvement consistent with left sphenoid sinusitis. She was then referred to the ear, nose and throat department and had endoscopic transnasal sphenoidotomy in theatre. Culture results showed Haemophilus influenza and fungal pseudohyphae. She recovered three months later after a course of antibiotics and antifungals. The onset of isolated sphenoid sinus disease is often insidious and the diagnosis of this condition remains a challenge. Magnetic resonance imaging and computed tomography remain the best diagnostic tools to recognise and manage this condition.

[Improvement of surgical treatment of Duane syndrome in children]. / Sovershenstvovanie khirurgicheskogo lecheniya sindroma Dueina u detei.

PURPOSE: To analyze the use of bifurcation of the lateral rectus muscle (LRM) in the surgical treatment of Duane syndrome (DS) in children. MATERIAL AND METHODS: The analysis of surgical treatment involved 12 children with paralytic strabismus at the age of 8 to 17. The following research methods were conducted for all patients: the study of eye motility in different directions of gaze, the study of eyes position and the degree of deviation in different positions of gaze, the Bielschowsky test, the Park's three-step test, determination of the nature of torticollis, the forcing test - intraoperative forceps test, multislice computed tomography (MSCT) of the head and orbit, ultrasonography of the oculomotor muscles. All study children underwent bifurcation (Y-cleavage procedure) of LRM with recession in exo-DS in 17% of cases, without recession in eso-DS - 83% of cases, respectively. RESULTS: In all operated patients with Duane syndrome, the direction of LRM was compensated (downshoot and upshoot were eliminated). In a direct gaze, the correct position was achieved in 10 (83%) cases, in 2 (17%) the residual angle of up to 10 PD remained, and torticollis was eliminated in 9 (75%) patients. CONCLUSION: The method of LRM bifurcation - the procedure of dividing the muscle into two portions and changing its primary localization, accompanied by abnormalities (presence of deviation, retraction, anomalous vertical movements, limited ocular motility, etc.), - helps compensate for them, and provides cosmetic as well as functional improvement.

Association of lateral rectus muscle volume and ocular motility with the abducens nerve in Duane's retraction syndrome.

PURPOSE: To investigate the relationship between ocular motility and lateral rectus (LR) muscle volume according to the presence or absence of the abducens nerve in patients with Duane's retraction syndrome (DRS) using high-resolution magnetic resonance imaging (MRI). METHODS: A total of 54 unilateral DRS patients were divided into two groups according to high-resolution MRI findings: DRS without an abducens nerve on the affected side (absent CN6 group, n = 45) and DRS with symmetric abducens nerves on both sides (present CN6 group, n = 9). Ocular motility was measured by image analysis based on nine gaze photographs. LR volume was measured on T2-weighted coronal MRI of the orbit, and the ratio of paretic/normal side (P/N) LR volume was investigated. Association of the abducens nerve with various parameters including ocular motility, LR volume, and ratios of P/N LR volume were determined. RESULTS: LR volume was smaller in the affected eye than the non-affected eye in both groups. In the present CN6 group, abducens nerve diameter and the ratio of P/N LR volume showed a positive correlation. A smaller LR volume and more limitation of abduction in the affected eye were predictive of an absent abducens nerve in DRS. CONCLUSIONS: LR muscle hypoplasia was apparent in the affected eye of DRS patients. Abducens nerve diameter positively correlated with the ratio of P/N LR volume in the present CN6 group. Graphical abstract.

Laser-Assisted Adjustable Suture Technique in Strabismus Surgery.

PURPOSE: The aim of this study was to assess the efficacy and safety of a new technique (argon laser-assisted lysis of the adjustable suture) in strabismus surgery. PATIENTS AND METHODS: Recession of lateral rectus muscle was done and was secured to the sclera at the predetermined recession position after suspending it 1.5-2.5 mm farther. A 10-0 nylon suture was placed at the original insertion site, passed under the previously tied muscle suture knot, and tied, advancing the muscle to the new scleral insertion. Postoperatively in the same day of surgery, if the targeted slight overcorrection was not achieved, a topical anesthetic was given, and argon laser was used to cut the nylon suture providing additional muscle recession. RESULTS: Forty-two patients with exotropia were included: 11 children and 31 adults. Eleven (26.2%) patients became orthophoric immediately following muscle recession. Thirty-one (73.8%) patients were undercorrected with a mean residual angle of 8.2±3.3 pd. After laser-assisted release of the suture, 12 (28.6%) patients were orthophoric, with 4 (9.5%) patients still undercorrected and 26 (61.9%) patients overcorrected. By the end of 6 months postoperatively, the overall success rate of the procedure was 88.1%, with only 5 (11.9%) patients with exotropia. CONCLUSION: The laser-assisted adjustable suture technique had an overall success rate of 88.1% with only 11.9% of the patients showing exotropia. The technique can help achieve successful alignment.

Surgical outcomes related to degree of unilateral lateral rectus muscle recession in intermittent exotropia of 20 prism diopters.

PURPOSE: We compared the surgical results of different degrees of unilateral lateral rectus muscle recession (ULR) and investigated the surgical outcomes and factors related to recurrence of intermittent exotropia of 20 prism diopters (PD). STUDY DESIGN: Retrospective study. METHODS: The study comprised 163 patients with intermittent exotropia of 20 PD who underwent ULR between January 2010 and May 2015 and at least 2 years of follow-up after the initial surgery. The patients were divided into 3 groups according to the extent of ULR (8.0, 8.5, or 9.0 mm), and the surgical results were compared. We investigated the surgical outcomes and factors related to recurrence. RESULTS: The mean postoperative follow-up period was 3.89 ± 1.82 years. The rate of recurrence within 2 years differed clinically (8.0 mm: 25.7%; 8.5 mm: 19.0%; 9.0 mm: 8.6%). However, other factors did not significantly differ among the groups. The comparison of the recurrence and the nonrecurrence groups showed that the age at the time of surgery varied significantly (recurring: 6.5 years, nonrecurring: 8 years; P = 0.012). A younger age at the time of surgery and a ULR of 8.0 mm were significant risk factors for the recurrence of ULR in intermittent exotropia of 20 PD. CONCLUSION: We suggest that a surgical dose of 9.0 mm ULR is preferable to 8.0 mm ULR for intermittent exotropia of 20 PD.

Binocular discrepancy in lateral rectus muscle attachment in intermittent exotropia with eye dominance.

PURPOSE: To determine whether there is asymmetry in the lateral rectus (LR) muscle attachment between both eyes in patients with intermittent exotropia (IXT) with a non-dominant eye, but without amblyopia or anisometropia. METHODS: In total, 109 patients who underwent bilateral lateral rectus recession for IXT were included, 81 with and 28 without eye dominance. The limbus-insertion distance and tendon width of the LR muscle were measured intraoperatively using callipers. The insertion-equator distance (presumed arc of contact), area of contact (arc of contact × tendon width), and torque value (radius of globe × arc of contact) of the LR muscle were calculated based on intraoperative measurements and axial length measured using a partial interferometer. Parameters regarding LR muscle attachment were compared between fellow eyes and between groups. RESULTS: Mean measurements in all parameters related to LR muscle attachments other than tendon width were not different between the two eyes or between groups. The mean tendon width of the non-dominant eye was 9.2 ± 0.7 mm, narrower than the 9.4 ± 0.5 mm width in either eye of patients without dominance (p = 0.020). However, there was no difference in all parameters in 21 pairs of patients after matching. The proportion of patients who showed binocular discrepancies in attachment measurements beyond that attributable to potential measuring errors did not differ between the two groups. CONCLUSIONS: Structural parameters related to LR muscle attachments did not differ based on eye dominance, suggesting that the anatomic structure of LR muscle attachments is not responsible for eye dominance in IXT.

Clinical Manifestations of Delayed-onset Consecutive Esotropia after Surgical Correction of Intermittent Exotropia.

PURPOSE: To evaluate the clinical features and prognosis of a delayed-onset consecutive esotropia (ET) after surgical correction of intermittent exotropia. METHODS: Thirty-four patients who developed consecutive ET after primary bilateral lateral rectus recession for the surgical correction of intermittent exotropia were evaluated retrospectively and were divided into two groups: delayed-onset consecutive ET group and the continuous consecutive ET group. Patients who developed esodeviation after once recovering to orthotropia within 1 month after the operation were included in the delayed-onset consecutive ET group, and patients with continuous esodeviation after the operation were included in the continuous consecutive ET group. We evaluated preoperative and postoperative angle of deviation, suppression, stereopsis, and follow up periods between the two groups and compared re-operation and success following non-surgical treatment between the continuous consecutive ET group and the delayed-onset consecutive ET group. RESULTS: Among 34 patients with consecutive ET, 27 patients (79.4%) were included in the delayed-onset consecutive ET group, and seven patients (23.3%) were included in the continuous group. Success rate of non-surgical treatment was not statistically significant between two groups (p = 0.55), but it was higher in the delayed-onset group with 37.5%, and 25% of patients in continuous group were successfully recovered to straight alignment. Duration of orthotropia in delayed-onset group was 7.4 ± 6.0 months (range, 2-29 months). Age, sex, preoperative refractive error, preoperative exodeviation, suppression, and near steroacuity were not statistically significant between two groups (p > 0.05, all). In the delayed-onset group, three patients (11.1%) underwent re-operation, while three patients (42.9%) in continuous consecutive ET group underwent re-operation (p = 0.048). CONCLUSIONS: Re-operation rate of delayed-onset consecutive ET after surgical correction of intermittent exotropia was lower than that of continuous consecutive ET.

Comparison of lateral and medial rectus muscle in human: an anatomical study with particular emphasis on morphology, intramuscular innervation pattern variations and discussion on clinical significance.

This paper aims to present various aspects of the anatomy of horizontal (i.e., lateral and medial) rectus muscles. It mainly compares morphology and detailed patterns of intramuscular innervation of those muscles. It is also one of the first reports that uses the Sihler's stain to examine human extraocular muscles. The study was conducted on 80 isolated cadaveric hemi-heads. Sihler technique of nerves staining served to expose the course of intramuscular branches of the oculomotor and abducens nerves. The lateral rectus was longer (48 mm versus 46.5 mm) and more distant from the limbus (6.8 mm versus 5.7 mm) than the medial rectus muscle. Three variants of the abducens nerve primary division were observed in the lateral rectus muscle. In the medial rectus muscle, the motor branch from the oculomotor nerve was more evenly divided into sub-branches. In both examined horizontal rectus muscles, primary muscular branches split into secondary sub-branches, which undergo numerous further divisions. The most numerous terminal sub-branches formed the terminal plexus. The distance between the insertion and the anterior-most end of the terminal plexus referenced to the total length of the muscle ranged from 35.4 to 48.5% for the lateral rectus muscle and from 36.3 to 50.5% for medial rectus muscle. Both horizontal rectus muscles share similar general pattern of distribution of intramuscular nerves, with characteristic root-like arborizations of sub-branches. The terminal nerve plexus was observed near half of both muscles' length. Knowledge of variations and innervation pattern of the extraocular muscles may be relevant during ophthalmology surgeries.

Intramuscular innervation of the lateral rectus muscle evaluated using sihler's staining technique: Potential application to strabismus surgery.

The latest research suggests that the abducens nerve may be divided into subbranches that reach functionally distinct zones of the lateral rectus muscle. The goal of the study was to examine this muscle's innervation, including the detailed distribution of the intramuscular subbranches of the abducens nerve. Twenty-five lateral rectus muscle specimens were harvested (with the orbital segment of the abducens nerve), fixed in 10% formalin solution, and stained with Sihler's whole mount nerve staining technique. Subbranches running to the lateral rectus divided into two main groups: superior and inferior. Both groups of subbranches are distributed in a fan-shaped manner, show a characteristic "tree-like" branching pattern and form terminal plexus near the proximal half of the lateral rectus muscle. However, some smaller subbranches run as far as the muscle's insertion, and recurrent subbranches also reach its origin. With respect to their course to the muscle's origin or insertion, the smallest subbranches running within the muscle may be associated with innervation of the tendon. In the majority of cases (88%), superior and inferior subbranches of the abducens nerve overlapped in the central one-third of the lateral rectus muscle's width so that any clearly distinct anatomical segments of the muscle could be observed based on Sihler's technique. In the remaining 12% of specimens, superior and inferior groups of subbranches innervated two distinct compartments of the lateral rectus muscle with no overlapping. Dense, fan-shaped distribution of abducens nerve intramuscular subbranches can be observed within the lateral rectus muscle. Clin. Anat. 33:585-591, 2020. © 2019 Wiley Periodicals, Inc.

Changes in the Effects of Bilateral Lateral Rectus Muscle Recession According to Preoperative Angle Deviation

PURPOSE: To investigate how the effect of bilateral rectus muscle recession changed by analyzing the effect/dose ratio of surgery according to the preoperative angle deviation.METHODS: We retrospectively studied the medical records of patients from January 2007 to March 2014 who underwent bilateral lateral rectus muscle recession and who visited our hospital for at least 2 years after surgery. We classified the patients into two groups: the preoperative large angle deviation group (35 prism diopters [PD] or more) and the small angle deviation group (20 PD or less). We observed exodrift patterns by measuring distant and near angle deviation according to the preoperative and postoperative times. The effect/dose ratio of recession was calculated at each visit. Surgical success was defined as an alignment between 10 PD of exodeviation and 5 PD of esodeviation, both at distance and at near.RESULTS: Among 165 patients, 84 patients were in the large angle deviation group and 81 patients were in the small angle deviation group. Preoperative angle deviation of the large angle deviation group was 39.34 ± 5.13 PD (range: 35–55 PD) and the small angle deviation group was 19.49 ± 1.62 PD (range: 18-20 PD) (p < 0.001). At postoperative 1 day, the alignments of eyes of the two groups were −8.32 ± 9.31 PD and −13.11 ± 6.94 PD; p < 0.001, respectively. At the date of the final follow-up, the alignments of eyes of the two groups were 4.63 ± 8.94 PD and 1.22 ± 8.01 PD; p = 0.011, respectively, and the effect/dose ratios were 2.25 ± 0.62 PD/mm and 1.94 ± 0.78 PD/mm, respectively, which meant that the effect of correction for the large angle deviation group was larger than that of the small angle deviation group (p = 0.005). Both groups showed postoperative exodrift patterns and similar success rates (75.0% and 80.2%, respectively), which showed no significant difference (p = 0.268).CONCLUSIONS: The small angle deviation group showed a larger effect of correction and high exodrift pattern at the postoperative initial time and the large angle deviation group showed a smaller effect of correction and low exodrift pattern at the postoperative initial time. The preoperative angles of deviation and the operative success rates were not related.

[Unilateral exophthalmos revealing ruptured giant intracavernous aneurysm of the ruptured internal carotid artery: clinical case]. / Exophtalmie unilatérale révélant un géant anévrysme intra caverneux rompu de la carotide interne rompu.

Giant aneurysm of the intracranial carotid artery is a relatively rare disorder which can lead to life-threatening consequences. Ophthalmologic symptoms, mainly oculomotor nerve palsies, usually reveal lesions of the cavernous sinuses. We report the case of a 39-year old female patient presenting with rapidly progressive unilateral exophthalmos (A, B) and binocular diplopia associated with headaches affect one half of the head causing a single episode of vomiting evolving in a context of apyrexia and general state preservation. Ophthalmologic examination showed isolated palsies of the right lateral rectus muscle (abduction deficit). Static and dynamic assessment of the eyelids was normal. Corrected visual acuity was 5/10. Slit lamp exam showed dilation of the conjunctival vessels (C), clear cornea that didn't take up fluorescein, preserved direct and consensual pupillary light reflex, intra-ocular pressure 15 mmhg and venous tortuosities at the back of the eye, without papillary abnormalities (D). Neuroradiological assessment, such as magnetic resonance angiography, showed compressive aneurysms of the intracavernous portion of the right internal carotid artery with grade III exophthalmos. Cerebral angiography objectified right giant ruptured saccular cavernous carotid aneurysm in the cavernous sinuses (E) with anterior and posterior venous drainage associated with aneurysm of the left carotid syphon (F).

Congenital Multiple Ocular Motor Nerve Palsy Complicated by Splitting of the Lateral Rectus Muscle.

We report a case of congenital multiple ocular motor nerve palsy combined with splitting of the lateral rectus muscle (LR). A 59-year-old Japanese female was investigated for worsening esotropia after corrective surgery. She presented with left hypertropia (35Δ) and esotropia (45-50Δ). Orbital magnetic resonance imaging (MRI) showed reduced belly sizes in the superior rectus, inferior rectus, and superior oblique muscles and splitting of the LR, extending from the origin to the belly, in the left eye. Splitting of the LR belly was detected on MRI in a case of congenital multiple ocular motor nerve palsy.

Lateral rectus muscle recession and the vertical palpebral fissure height: to do or not to do inter-muscular septum dissection?

In this study, we aimed to evaluate changes of vertical palpebral fissure height (VPFH) after unilateral lateral rectus muscle recession. Twenty-five and twenty-six patients who were candidates for lateral rectus muscle recession were assigned into "with" and "without" intermuscular septum dissection study arms. The VPFH was measured at one-day before surgery and in two weeks and three months, postoperatively. Three months after surgery, significant increase of VPFH was observed in both groups (Paired t-test; P=0.005). Also, less widening of VPFH was observed in "with intermuscular septum dissection" group (Change in VPFH in "with intermuscular septum dissection" vs "without intermuscular septum dissection" groups: 0.48 mm vs 1.34 mm; ANCOVA test; P<0.001). However, such results were not observed two weeks post-operatively (Change in VPFH in "with intermuscular septum dissection" vs "without intermuscular septum dissection" groups: -0.28 mm vs 0.28 mm; ANCOVA test; P=0.302). Intermuscular septum dissection is recommended in lateral rectus muscle recession to partially prevent the undesirable increment of VPFH.

Identification of Functional Cell Groups in the Abducens Nucleus of Monkey and Human by Perineuronal Nets and Choline Acetyltransferase Immunolabeling.

The abducens nucleus (nVI) contains several functional cell groups: motoneurons of the singly-innervated twitch muscle fibers (SIF) and those of the multiply-innervated muscle fibers (MIF) of the lateral rectus muscle (LR), internuclear neurons (INTs) projecting to the contralateral oculomotor nucleus (nIII) and paramedian tract-neurons (PMT) that receive input from premotor neurons of the oculomotor system and project to the floccular region. In monkey, these cell populations can be delineated by their chemical signature. For correlative clinico-pathological studies the identification of the homologous cell groups in the human nVI are required. In this study, we plotted the distribution of these populations in monkey nVI by combined tract-tracing and immunohistochemical staining facilitating the identification of homologous cell groups in man. Paraffin sections of two Rhesus monkeys fixed with 4% paraformaldhehyde and immunostained with antibodies directed against choline acetyltransferase (ChAT) as marker enzyme for cholinergic neurons and chondroitin sulfate proteoglycan (CSPG) to detect perineuronal nets (PNs) revealed four neuron populations in nVI with different chemical signatures: ChAT-positive and CSPG-positive SIF motoneurons, ChAT-positive, but CSPG-negative MIF motoneurons, and ChAT-negative neurons with prominent PNs that were considered as INTs. This was confirmed by combined immunofluorescence labeling of cholera toxin subunit B (CTB) or wheat germ agglutinin (WGA) and ChAT or CSPG in nVI sections from cases with tracer injections into nIII. In the rostral part of nVI and at its medial border, populations of ChAT-negative groups with weak CSPG-staining, but with strong acetylcholinesterase (AChE) activity, were identified as PMT cell groups by correlating them with the location of anterograde tracer labeling from INTs in nIII. Applying ChAT- and CSPG-immunostaining as well as AChE staining to human brainstem sections four neuron groups with the same chemical signature as those in monkey could be identified in and around the nVI in human. In conclusion, the distribution of nVI neuron populations was identified in human based on findings in monkey utilizing their markers for cholinergic neurons and their different ensheathment by PNs of the extracellular matrix.

Unilateral lateral rectus muscle advancement surgery based on one-fourth of the angle of consecutive esotropia.

BACKGROUND: To evaluate the efficacy of unilateral lateral rectus muscle advancement surgery based on one-fourth of the angle of consecutive esotropia within 25 prism diopters (PD) occurring after bilateral lateral rectus muscle recession for intermittent exotropia. METHODS: Medical records of 11 patients who underwent unilateral lateral rectus muscle advancement for consecutive esotropia from 2011 to 2014 and who were observed for at least 6 months after surgery were retrospectively reviewed. The change in angle of deviation from before to after consecutive esotropia surgery, as well as the success rate and surgical effect, were evaluated. RESULTS: Preoperative esodeviation was -19.6 ± 4.7 PD [median - 20.0 PD, interquartile range (IQR) 9.0] at distance and -16.5 ± 7.4 PD [median - 18.0 PD, IQR 17.0] at near. The mean surgical amount of unilateral lateral rectus muscle advancement surgeries, based on one-fourth of the angle of consecutive esotropia, was 4.8 ± 1.1 mm [median 5.0 mm, IQR 2.0]. Of the 11 patients, 10 (91%) recovered to orthotropia or exodeviation within 8 PD. The surgical effects of unilateral lateral rectus muscle advancement were 3.3 ± 0.7 PD/mm [median 3.6 PD/mm, IQR 1.0] after 1 day, 3.7 ± 0.6 PD/mm [median 3.8 PD/mm, IQR 1.0] after 1 week, and 3.8 ± 0.7 PD/mm [median 3.8 PD/mm, IQR 1.5] after 6 months. CONCLUSIONS: Unilateral lateral rectus muscle advancement surgery based on one-fourth of the angle of consecutive esotropia within 25 PD was successful in all 11 patients. The surgical effect was significantly greater in unilateral lateral rectus muscle advancement than in primary lateral rectus muscle recession. Reduction in the amount of surgery should be considered carefully in unilateral lateral rectus muscle advancement for consecutive esotropia.

Detailed anatomy of the abducens nerve in the lateral rectus muscle.

The aims of this study were to elucidate the detailed anatomy of the abducens nerve in the lateral rectus muscle (LRM) and the intramuscular innervation pattern using Sihler staining. In this cohort study, 32 eyes of 16 cadavers were assessed. Dissection was performed from the LRM origin to its insertion. The following distances were measured: from LRM insertion to the bifurcation point of the abducens nerve, from LRM insertion to the entry site of the superior branch or inferior branch, from the upper border of the LRM to the entry site of the superior branch, from the lower border of LRM to the entry site of inferior branch, and the widths of the main trunk and superior and inferior branches. The single trunk of the abducens nerve divided into two branches 37 mm from insertion of the LRM, and 22 of 32 (68.8%) orbits showed only two superior and inferior branches with no subdivision. The superior branch entered the LRM more anteriorly (P = 0.037) and the superior branch was thinner than the inferior branch (P = 0.040). The most distally located intramuscular nerve ending was observed at 52.9 ± 3.5% of the length of each muscle. Non-overlap between the superior and inferior intramuscular arborization of the nerve was detected in 27 of 32 cases (84.4%). Five cases (15.6%) showed definite overlap of the superior and inferior zones. This study revealed the detailed anatomy of the abducens nerve in the LRM and provides helpful information to understand abducens nerve palsy. Clin. Anat. 30:873-877, 2017. © 2017 Wiley Periodicals, Inc.

Relationship of the Lateral Rectus Muscle, the Supraorbital Nerve, and Binocular Coordination with Episodic Tension-Type Headaches Frequently Associated with Visual Effort.

Objective: To study the relationship between tension-type headaches and the oculomotor system in terms of binocular coordination, mechanosensitivity of the supraorbital nerve, and myofascial trigger points in the lateral rectus muscle, assessing the influence of visual effort caused by using a computer at work. Design: Observational study with blind evaluation of the response variable. Methods: Two groups were compared: 19 subjects with tension-type headaches and 16 healthy subjects, both exposed to computer use at work. A blinded assessor conducted three tests: measurement of the supraorbital nerve pressure pain threshold using a pressure algometer, evaluation of myofascial trigger points of the lateral rectus using the verbal numerical scale, and assessment of binocular coordination in smooth pursuit eye movements using an innovative video-oculography system. Tests were performed before work began and four hours later, and subjects in the headache group were examined when they presented a headache score of less than or equal to 3 on the verbal numerical scale. Results: The headache group presented a greater sensitivity of the supraorbital nerve and greater local and referred pain of the lateral rectus ( P < 0.05). Visual effort caused a significant worsening of these variables in both groups. However, binocular coordination after visual effort was only significantly affected in the headache group ( P < 0.05), primarily in horizontal movements. Conclusions: The finding of a higher alteration of the sensitivity of the supraorbital nerve, the myofascial trigger points of the lateral rectus, binocular coordination, and the significant influence of visual effort in patients with tension-type headaches suggest a new clinical perspective for problems related to tension-type headaches.