Anatomical Relationship between the Inferior Temporal Septum and the Temporal Branch of the Facial Nerve for Clinical Applications.

BACKGROUND: The inferior temporal septum (ITS) is a fibrous adhesion between the superficial temporal fascia and the superficial layer of the deep temporal fascia. This study identified detailed the anatomical relationship between the ITS and the temporal branch of the facial nerve (TBFN) for facial nerve preservation during temple interventions. METHODS: Among 33 Korean cadavers, 43 sides of TBFNs in temporal regions were dissected after identifying the ITS between the superficial temporal fascia and superficial layer of the deep temporal fascia through blunt dissection. The topography of the ITS and TBFN were investigated with reference to several facial landmarks. Regional relationships with the ITS and TBFN within the temporal fascial layers were histologically defined from five specimens. RESULTS: At the level of the inferior orbital margin by the tragion, the mean distances from the lateral canthus to the anterior and posterior branches of the TBFN were 5 and 6.2 cm, respectively. At the lateral canthus level, the mean distance from the lateral canthus to the posterior branch of the TBFN was similar to that to the ITS, at 5.5 cm. At the superior orbital margin level, the posterior branch of the TBFN ran cranial to the ITS adjacent to the frontotemporal region. The TBFN ran through the subsuperficial temporal fascia layer and the nerve fibers located cranially, and within the ITS meshwork in the upper temporal compartment. CONCLUSION: The area of caution during superficial temporal fascia interventions related to the TBFN was clearly identified in the upper temporal compartment, which is known to lack important structures.

An Unexpected Complication Resulting from Radiofrequency Ablation for Treating Facet Joint Syndrome: A Case Report.

Lumbar facet joints have been identified as a potential source of chronic low back pain (LBP) in 15% to 45% of patients, with the prevalence of such pain varying based on specific populations and settings examined. Lumbar facet joint interventions are useful in the diagnosis as well as the therapeutic management of chronic LBP. Radiofrequency ablation (RFA) of medial branch nerves is recognized as a safe and effective therapy for chronic facet joint pain in the lumbosacral spine, and its efficacy has already been established. The use of RFA is currently widespread in the management of spinal pain, but it is noteworthy that there have been works in the literature reporting complications, albeit at a very low frequency. We present a case of third-degree skin burns following radiofrequency ablation (RFA) for the management of facet joint syndrome. Postoperatively, the patient's skin encircling the needle displayed a pallor and exhibited deterioration in conjunction with the anatomical anomaly. The affected area required approximately 5 months to heal completely. During RFA, heat can induce burns not only at the point of contact with the RF electrode but also along the length of the needle. Vigilant attention is necessary to ensure patient safety and to address any potential complications that may arise during the procedure, including the possibility of minor technical errors.

Effects of Gestational and Lactational Lead Exposure and High Fat Diet Feeding on Cerebellar Development of Postnatal Rat Offspring.

Obesity and heavy metals, such as lead (Pb), are detrimental to the adult brain because they impair cognitive function and structural plasticity. However, the effects of co-administration of Pb and a high-fat diet (HFD) on the developing cerebellum is not clearly elucidated. We investigated the effects of Pb exposure (0.3% lead acetate) on developing cerebellum in the pups of an HFD-fed obese rat model. One week before mating, we fed a chow diet (CD) or HFD to the rats for one week and additionally administered Pb to HFD-fed female SD rats. Thereafter, treatment with Pb and a HFD was continued during the gestational and lactational periods. On postnatal day 21, the pups were euthanized to sample the brain tissue and blood for further analysis. Blood Pb levels were significantly higher in HFD-fed rats than in CD-fed rats. Histologically, the prominent degeneration of Purkinje cells was induced by the co-administration of Pb and HFD. The calbindin-28Kd-, GAD67-, NMDAR1-, and PSD95-immunopositive Purkinje cells and inhibitory synapse-forming pinceau structures were significantly decreased following Pb and HFD co-administration. MBP-immunoreactive myelinated axonal fibers were also impaired by HFD but were significantly damaged by the co-administration of HFD and Pb. Oxidative stress-related Nrf2-HO1 signaling was activated by HFD feeding, and Pb exposure further aggravated oxidative stress, as demonstrated by the consumption of endogenous anti-oxidant in HFD-Pb rats. The pro-inflammatory response was also increased by the co-administration of HFD and Pb in the cerebellum of the rat offspring. The present results suggest that HFD and Pb treatment during the gestational and lactational periods are harmful to cerebellar development.

Topography of the frontal branch of the facial nerve and its clinical implication for temporal direct browplasty.

Due to anatomic proximity to the surgical site, iatrogenic trauma to the frontal branch of the facial nerve (FbFN) with resultant brow paralysis is a recognized major complication of temporal direct browplasty. This study was aimed to elucidate the course of the FbFN in the area superolateral to the brow in order to facilitate safer temporal direct browplasty by preventing facial nerve injury. Forty-five hemifaces from 32 embalmed Korean cadavers were dissected. A horizontal line connecting the tragion to lateral canthus was established. Then, an oblique line passing through the lateral canthus and 45° to the horizontal line was used as reference line. The mean distance from the lateral canthus to the points where the FbFN cross the reference line was measured. The angle between the FbFN and reference line at the crossing points were also recorded. After crossing the zygomatic arch, FbFN continues in an anteriorly inclining curve across the temporal region, passing near the lateral end of the brow as it heads toward frontalis muscles. During the course, the FbFN laying in the innominate fascial layer was divided into 3 branches. The anterior and posterior branch of FbFN crossed the reference line superiorly and laterally at 3 and 4 cm from the lateral canthus, respectively. In conclusion, the oculofacial surgeon must bring the dissection plane of the forehead tissue more superficially around the 3 cm superolaterally to the lateral canthus in the direction of 45° from the horizontal line in order to avoid nerve injury.

Coccydynia: anatomic origin and considerations regarding the effectiveness of injections for pain management.

Coccydynia is a debilitating pain disorder. However, its pathophysiology is not well understood. When approaching coccydynia, the exact underlying cause of pain must be identified to develop an appropriate treatment plan. The specific approach to coccydynia can vary depending on an individual's condition and the underlying cause. Thorough evaluation by a pain physician is essential to determine the most appropriate course of treatment. The purpose of this review is to examine the various causes contributing to coccygeal pain and specifically focus on the exact anatomical neurostructures, such as the anococcygeal nerve, perforating cutaneous nerve, and ganglion impar. We also reviewed the relevant clinical outcomes and suggested recommendations for each anatomical structure.

Treatment outcomes of modified argon laser photocoagulation for conjunctivochalasis.

To determine the effectiveness of conjunctivoplasty using a modified argon laser photocoagulation method on patients with conjunctivochalasis (CCh). This study included 25 cases of symptomatic inferior CCh. After staining the surface of a redundant conjunctiva using a dark-purple marker, low-energy argon laser photocoagulation (500 µm spot size for 0.5 seconds at power 300 mW) was applied under topical anesthesia for a mean of 80 times. The patients were aged 67.6 ±â€…7.1 years (mean ±â€…standard deviation). During a mean follow-up period of 7.8 months (range of 6-12 months), the CCh grades of 21 eyes (84%) decreased after laser conjunctivoplasty. Calculated reduction rates of grades 1, 2, and 3 were 90%, 75%, and 67%, respectively. Patient subjective symptoms were improved in 80% of cases. No postoperative complications such as conjunctival scarring or persistent ocular irritation were observed. Our modified argon laser photocoagulation method employs staining the conjunctival surface to increase the thermal laser energy absorbed by the target. This novel technique is simple and effective for treating mild-to-moderate-grade CCh in outpatient clinics.

Anatomical study of the adductor canal: three-dimensional micro-computed tomography, histological, and immunofluorescence findings relevant to neural blockade.

BACKGROUND: A precise anatomical understanding of the adductor canal (AC) and its neural components is essential for discerning the action mechanism of the AC block. We therefore aimed to clarify the detailed anatomy of the AC using micro-computed tomography (micro-CT), histological evaluation, and immunofluorescence (IF) assays. METHODS: Gross dissections of 39 thighs provided morphometric data relevant to injection landmarks. Serial sectional images of the AC were defined using micro-CT and ultrasonography. The fascial and neural structures of the AC proper were histologically evaluated using Masson's trichrome and Verhoeff-Van Gieson staining, and double IF staining using choline acetyltransferase (ChAT) and neurofilament 200 antibodies. RESULTS: The posteromedial branch insertion of the nerve to vastus medialis (NVM) into the lateral border of the AC proper was lower (14.5 ± 2.4 cm [mean ± SD] above the base of the patella) than the origin of the proximal AC. The AC consists of a thin subsartorial fascia in the proximal region and a thick aponeurosis-like vastoadductor membrane in the distal region. In the proximal AC, the posteromedial branch of the NVM (pmNVM) consistently contained both sensory and motor fibers, and more ChAT-positive fibers were observed than in the saphenous nerve (27.5 ± 11.2 / 104 vs. 4.2 ± 2.6 / 104 [counts/µm2], P < 0.001). CONCLUSIONS: Anatomical differences in fascial structures between the proximal and distal AC and a mixed neural component of the neighboring pmNVM have been visualized using micro-CT images, histological evaluation, and IF assays.

An anatomical and radiological study of the tectorial membrane and its clinical implications.

The radiological image of an intact tectorial membrane (TM) became an important favorable prognostic factor for craniovertebral instability. This study visualized the fascial layers of the TM and adjacent connective tissues with clinical significance by micro-CT and histological analysis. The TM firmly attached to the bony surface of the clivus, traversed the atlantoaxial joint posteriorly, and was inserted to the body of the axis showing wide distribution on the craniovertebral junction. The supradental space between the clivus, dens of the axis, anterior atlantooccipital membrane, and the TM contained profound venous networks within the adipose tissues. At the body of the axis, the compact TM layer is gradually divided into multiple layers and the deeper TM layers reached the axis while the superficial layer continued to the posterior longitudinal ligament of the lower vertebrae. The consistent presence of the fat pad and venous plexus in the supradental space and firm stabilization of the TM on the craniovertebral junction was demonstrated by high-resolution radiologic images and histological analysis. The evaluation of the TM integrity is a promising diagnostic factor for traumatic craniovertebral dislocation.

Modified argon laser therapy for benign tumor of the eyelid.

BACKGROUND: To report about the therapy of benign eyelid tumors with a modified argon laser technique as an alternative to surgery. METHODS: Nineteen benign tumors of the eyelid were included in this study. After staining the surface of the tumor with a violet marker, low-energy argon laser photoablation was performed. A mean number of 312 spots (spot size ranging from 150 to 500 µm) with a power of 200 to 400 mW, and a duration between 0.1 and 0.2 s were applied. RESULTS: The eyelid tumors were located mainly in the lower eyelid (58%). Dermal nevi and papilloma were the most frequently treated lesions. Over a mean follow-up period of 10.5 months (range 6-18 months), all eyelid tumors were successfully treated by a single session of laser therapy. All patients were satisfied with the laser therapy and the cosmetic result. No postoperative complications were observed. No relapses occurred during follow-up. CONCLUSIONS: Our modified method of argon laser therapy utilizes the staining of the surface of the eyelid tumor to increase the amount of thermal laser energy absorbed by the target. This novel technique is simple and effective for treating benign eyelid tumors.

Morphological changes after lower eyelid epiblepharon surgery in Asian children.

BACKGROUND: This study aimed to determine the morphological changes in Asian lower eyelid epiblepharon patients after surgery. METHODS: The medical records of 59 patients who underwent lower eyelid epiblepharon repair were reviewed retrospectively. Eighty-nine patients who underwent strabismus surgery were set as the control group. The photographs for each group were analyzed based on the following factors: inferior half area (IHA) of the eye, eyelash angular direction (EAD), angle between the eyelashes and the cornea, marginal reflex distance 1 (MRD1) and marginal reflex distance 2 (MRD2). RESULTS: After surgery, the medial EAD changed from 92.45° ± 20.21° (mean ± SD) to 79.43° ± 23.31°, while the central and lateral EADs were unchanged. IHA increased from 36.33 ± 9.78 mm3 to 43.06 ± 10.57 mm3, and MRD1 increased from 1.92 ± 0.99 mm to 2.50 ± 0.93 mm, whereas MRD2 did not change. The mean angle between the eyelashes and the cornea increased from 39.64° to 72.19° immediately postoperatively, but had reduced to 58.75° 3 months later, followed by no further significant change at the 6-month and 9-month postoperative follow-ups. CONCLUSIONS: There is morphological changes of the eyelid after lower eyelid epiblepharon surgery, with increases in the IHA and MRD1. In addition, contact between the eyelashes and the cornea occurred mainly in the medial portion of the eyelid the position, which everted and stabilized over 3 months. Thus, follow-up observations are required for at least 3 months to properly evaluate the surgical outcome.

Investigation of the Orbital Arterial Distribution Using Image Superimposition to Determine Safe Zones for Retrobulbar Injection and to Prevent Filler Complications.

BACKGROUND: Retrobulbar filler injection has recently been considered an ideal method for orbital volume enhancement due to its nontoxic, easily reversible, and noninvasive characteristics. This study determined the arterial distribution in the orbit with the aim of defining a safety zone for retrobulbar filler injections used to enhance the orbital volume. METHODS: Twenty-seven orbits of 24 formalin-embalmed cadavers were dissected. The orbital arteries were identified after removal of the eyeball, extraocular muscles, and connective tissues. The course of each orbital artery was then recorded in each specimen, and all of the courses were then superimposed to determine the arterial distribution in the orbit. RESULTS: The superimposition of lined images based on the orbital vasculature of each specimen revealed that the arterial density was highest in the superonasal region and lowest in the inferotemporal region. In particular, orbital arteries were scarce at 8 o'clock and 4 o'clock in the right and left orbits, respectively, and an artery-free zone was demonstrated in the outer part of those directions. CONCLUSIONS: When performing a transcutaneous retrobulbar injection of filler for orbital volume enhancement, the relative safety zone could be considered to be located at 8 o'clock and 4 o'clock in the right and left orbits, respectively. The detailed topographic information about the arterial distribution in the orbit, provided by the present study, may help oculofacial surgeons to avoid injury to major vessels and decrease the risk of retrobulbar hemorrhage and vision-threatening complications.

Improvement in Near Vision Following Silodosin Treatment in Patients With Lower Urinary Tract Symptoms.

PURPOSE: The objective of this study was to investigate the change in near visual function after the administration of oral silodosin to patients with lower urinary tract symptoms (LUTS). METHODS: This prospective study included treatment-naive patients who were scheduled to start treatment with silodosin for LUTS. A comprehensive ophthalmological evaluation including the near vision and the automated pupillometry was performed at baseline and after 3 months of silodosin treatment. For subjective assessment of near visual ability and satisfaction, a Near Activity Visual Questionnaire-10 (NAVQ-10) was also used at the same time (higher scores indicating worse quality). RESULTS: Of 23 patients enrolled in this study, 15 continued with silodosin (8 mg once daily) treatment for 3 months and completed a follow-up evaluation. The mean age of participants was 60.4±8.4 years. Distant visual acuity and spherical error were unchanged after silodosin treatment. However, near vision acuity (logMAR) was improved after treatment (right, 0.47±0.36 vs. 0.38±0.39, P=0.018; left, 0.41±0.37 vs. 0.31±0.34, P=0.068; both, 0.27±0.26 vs. 0.21±0.27, P=0.043). Pupil size under room light decreased significantly in both eyes (right, 3.77±0.60 vs. 3.16±0.58, P=0.001; left, 3.72±0.80 vs. 3.21±0.75, P=0.002). The Rasch scale at NAVQ-10 improved from 54.7±9.9 to 48.5±11.2 (P=0.004). CONCLUSION: This preliminary study demonstrated that highly selective alpha-1A adrenergic receptor antagonists such as silodosin improve near visual acuity and quality in patients with LUTS/benign prostatic hyperplasia. Decrease in pupil size caused by inhibition of adrenergic alpha 1 mediated contraction of iris dilator muscle is a possible mechanism underlying improved near vision.

Transconjunctival versus Transcutaneous Injection of Botulinum Toxin into the Lacrimal Gland to Reduce Lacrimal Production: A Randomized Controlled Trial.

The purpose of this study was to determine and compare the effects between injecting botulinum toxin A (BTX-A) transconjunctivally into the palpebral lobe and transcutaneously into the orbital lobe of the lacrimal gland in patients with epiphora due to lacrimal outflow obstruction. This randomized controlled study included 53 eyes of 31 patients with unilateral or bilateral epiphora. Patients were randomly allocated to receive an injection of BTX-A (3 units) either transconjunctivally (n = 15, 25 eyes) or transcutaneously (n = 16, 28 eyes). For objective assessments, the tear meniscus height and Schirmer's I test with topical anesthesia were measured at baseline and after 2, 6, 12, and 24 weeks of follow-up. Subjective evaluations were performed using the Munk score. After BTX-A injection, patients in both groups experienced significant objective and subjective reductions in tearing at all follow-up times compared to pre-injection (success rate 86.8%), and the effect lasted for a mean duration of 5.63 months. The two delivery routes showed similar clinical effectiveness for a single injected dose of BTX-A. In conclusion, injecting BTX-A via either a transconjunctival or transcutaneous route helps to reduce normal tear production and results in significant improvements in the symptoms in patients with epiphora.

Quantitative measurement of passive duction force tension in intermittent exotropia and its clinical implications.

PURPOSE: To evaluate the passive duction force (PDF) in extraocular muscles (EOMs) in patients with intermittent exotropia (IXT) using a quantitative tension-measuring device. METHODS: This prospective, case-control study enrolled 25 patients with IXT and 26 age- and sex-matched controls. PDF was measured under general anesthesia as the eyeball was rotated medially or laterally away from the direction of the force being tested. The preferred eye for fixation was determined using a cover-uncover test. RESULTS: The PDF in the IXT and control groups were 60.9 g and 52.1 g, respectively, for the lateral rectus (LR) (p = 0.046) and 53.0 g and 48.8 g for the medial rectus (MR) (p = 0.293). When the eyes were examined separately in the IXT group, the PDF of LR was larger in the nonpreferred eye for fixation than in the control group (p = 0.039), whereas there was no difference in the preferred eye for fixation (p = 0.216). Additionally, the relative PDF of LR in the nonpreferred eye compared to the ipsilateral PDF of MR was positively associated with the duration of manifest deviation (p = 0.042) and the average angle of the near and far deviations (p = 0.023). CONCLUSIONS: The PDF in the LR in patients with IXT in the nonpreferred eye for fixation was larger than normal and could increase with the duration of manifest deviation and the angle of deviation. Evaluating the PDF in EOMs could provide information that is useful for managing strabismus and understanding its pathophysiology.

Anatomic, histologic, and ultrasound analyses of the dorsum of the hand for volumetric rejuvenation.

BACKGROUND: Volumetric rejuvenation of the dorsum of the hand with fat grafting or injectable fillers has increased in popularity in recent years. It has become widely accepted that the dorsum of the hand contains three fatty laminae: superficial, intermediate, and deep laminae. The dorsal venous plexus and dorsal cutaneous nerves are known to reside in the dorsal intermediate lamina. However, the superficial vein and cutaneous nerve might not be located in the same layer of subcutaneous tissue, as is the case in other body regions. MATERIALS AND METHODS: Eight hands were dissected in a layer-by-layer fashion from the skin to the extensor tendons. In another 13 hands from among 21 investigated cadavers, samples from the dorsum of the hand were harvested and stained using trichrome stains for histologic analysis. B-mode ultrasound was also performed for identifying structures of the dorsum of the hand. RESULTS: Anatomic dissection and histologic analysis of the dorsum of the hand revealed the presence of an unknown fascia in addition to the three known fascial layers. The additional fascia was located in the dorsal intermediate lamina and separated it into two compartments: one containing the dorsal venous plexus superficially and the other containing the dorsal cutaneous nerves deeply. Ultrasound showed corresponding structures including three hyperechoic fascial layers, three hypoechoic laminae, and additional hyperechoic fascia in dorsal intermediate lamina. CONCLUSIONS: Accurate anatomic knowledge of the dorsum of the hand will help practitioners determine the optimal and safe locations for performing fat grafting and injecting dermal fillers.

New instrument for quantitative measurements of passive duction forces and its clinical implications.

PURPOSE: Evaluating the passive duction force of the extraocular muscles is important for the diagnosis of and surgical planning for strabismus. This is especially relevant in patients with an observable limitation of duction movement. The purpose of this study was to validate passive duction forces in healthy subjects using a novel instrument. METHODS: An instrument for making continuous quantitative measurements of passive duction forces was designed. Tension was measured as the eyeball was rotated horizontally or vertically from the resting position under general anesthesia 10 mm (50°) away from the direction of force to be tested (opposite side). RESULTS: Seventy eyes of 35 subjects were enrolled in this study (age range of 4-80 years and mean age of 36.3 years). The passive duction force was measured at 49.0 ± 15.3 g (mean ± standard deviation) for medial rotation, 44.8 ± 13.2 g for lateral rotation, 50.5 ± 14.8 g for superior rotation, and 53.5 ± 13.8 g for inferior rotation. The passive duction forces were similar for all gaze positions, but it was larger for inferior rotation than for lateral rotation (P = 0.009). The passive duction force was significantly larger for vertical rotation (51.9 ± 14.4 g) than for horizontal rotation (46.9 ± 14.4 g) (P = 0.006). The passive duction force did not differ significantly with sex (P = 0.355), side (P = 0.087), or age (P = 0.872). CONCLUSIONS: These measurements of passive duction forces in a healthy population provide valuable information for diagnosing specific strabismic problems and could be useful for increasing the precision of strabismus surgery. Graphical abstract.

Three-dimensional microstructures of the intracortical canals in the animal model of osteoporosis.

Osteoporosis is a major disease in aged women, increasing the risk for fractures accompanied by changes in the microarchitecture. The aim of this study was to investigate the three-dimensional (3D) histomorphology of femur diaphysis in the animal model for postmenopausal osteoporosis. The cortical bone of femur diaphysis of the rat was serially sectioned at a thickness of 5 µm and evaluated age-associated changes of the intracortical (osteonal) canal networks three-dimensionally. Cortical microstructures of 10-month old rats were not affected by ovariectomy. Intracortical canal networks were radial toward endosteal aspect and frequently interconnected across the neighboring canals with short arciform and irregular canals reminiscent for resorption spaces in ovarectomized 16-month old rats, contrary to intact canals in 16-month old control rat. Increased proportion of the periosteal circumference lamella and deformed endosteal regions with rare cortical canals hampered reconstructive histomorphology in ovarectomized rats of 26 month age. We have shown that 3D reconstruction of rat femur of the aged model over 16-month old is suitable methods that evaluate and microstructural change of the intracortical canals and cortical bone porosity by estrogen depletion.

Macro/microscopic distribution of the dorsal nerve of penis in human glans penis.

This study aimed to elucidate the macroscopic and microscopic distributions of the dorsal nerve of penis (DNP) that provides the greatest sensitivity over the glans penis. The glandes of 23 penises of formalin-embalmed cadavers were investigated to confirm the macroscopic and microscopic distributions of the DNP within the glans penis by whole-mount Sihler's staining and histological sectioning. Superficial regions of the mid-glans were reconstructed in three dimensions to define the microstructure of terminal branches of the DNP that project towards the skin surface. A mean of 6.7 bundles of the DNP consisting of several nerve fibres converged linearly towards the distal end of the penis, rather than diverging laterally as they travelled. Lateral branches of the DNP extended linearly to the distal end with ramifications, while dorsomedial branches of the DNP gave off nerve fibres to the dorsum of the mid-glans and the corona. The intrastromal ramifications of the DNP were more developed in the distal half of the glans penis than the proximal glans containing the corpus cavernosum. These ramifications gave rise to radial nerve fibres that project towards the skin surface to form a plexiform network of terminal branches in the dermis. Linear projections of the main branches of the DNP throughout the glans and fine networks of terminal branches in the dermis were distinctly visualized in the human penis.

Intramuscular Nerves of the Inferior Rectus Muscle: Distribution and Characteristics.

PURPOSE: Knowledge of the distribution of intramuscular nerves of the extraocular muscles is crucial for understanding their function. The purpose of this study was to elucidate the intramuscular distribution of the oculomotor nerve within the inferior rectus muscle (IRM) using Sihler's staining. METHOD: Ninety-three IRM from 50 formalin-embalmed cadavers were investigated. The IRM including its branches of the oculomotor nerve was finely dissected from its origin to the point where it inserted into the sclera. The intramuscular nerve course was investigated after performing Sihler's whole-mount nerve staining technique that stains the nerves while rendering other soft tissues either translucent or transparent. RESULTS: The oculomotor nerve enters the IRM around the distal one-fourth of the muscle and then divides into multiple smaller branches. The intramuscular nerve course finishes around the distal three-fifth of the IRM in gross observations. The types of branching patterns of the IRM could be divided into two subcategories based on whether or not topographic segregation was present: (1) no significant compartmental segregation (55.9% of cases) and (2) a several-zone pattern with possible segregation (44.1% of cases). Possible compartmentalization was less clear for the IRM, which contained overlapping mixed branches between different trunks. CONCLUSION: Sihler's staining is a useful technique for visualizing the gross nerve distribution of the IRM. The new information about the nerve distribution and morphological features provided by this study will improve the understanding of the biomechanics of the IRM, and could be useful for strabismus surgery.