Non-Arteritic Ischemic Optic Neuropathy Following COVID-19 Vaccination in Korea: A Case Series

Background@#To report the clinical manifestations of non-arteritic anterior ischemic optic neuropathy (NAION) cases after coronavirus disease 2019 (COVID-19) vaccination in Korea. @*Methods@#This multicenter retrospective study included patients diagnosed with NAION within 42 days of COVID-19 vaccination. We collected data on vaccinations, demographic features, presence of vascular risk factors, ocular findings, and visual outcomes of patients with NAION. @*Results@#The study included 16 eyes of 14 patients (6 men, 8 women) with a mean age of 63.5 ± 9.1 (range, 43–77) years. The most common underlying disease was hypertension, accounting for 28.6% of patients with NAION. Seven patients (50.0%) had no vascular risk factors for NAION. The mean time from vaccination to onset was 13.8 ± 14.2 (range, 1–41) days. All 16 eyes had disc swelling at initial presentation, and 3 of them (18.8%) had peripapillary intraretinal and/or subretinal fluid with severe disc swelling. Peripapillary hemorrhage was found in 50% of the patients, and one (6.3%) patient had peripapillary cotton-wool spots. In eight fellow eyes for which we were able to review the fundus photographs, the horizontal cup/ disc ratio was less than 0.25 in four eyes (50.0%). The mean visual acuity was logMAR 0.6 ± 0.7 at the initial presentation and logMAR 0.7 ± 0.8 at the final visit. @*Conclusion@#Only 64% of patients with NAION after COVID-19 vaccination have known vascular and ocular risk factors relevant to ischemic optic neuropathy. This suggests that COVID-19 vaccination may increase the risk of NAION. However, overall clinical features and visual outcomes of the NAION patients after COVID-19 vaccination were similar to those of typical NAION.

Long-term Outcome of a Muscle Union Procedure in Patients with Horizontal Paralytic Strabismus

PURPOSE@#To report the long-term surgical outcomes of a muscle union procedure in patients with paralytic strabismus.@*METHODS@#We retrospectively reviewed the medical records of 20 patients who underwent muscle union procedure for paralytic strabismus from September 2010 to March 2018. We analyzed the clinical results before and at the final visit after surgery. We also compared the outcomes of the first year after surgery between patients with sixth cranial nerve palsy, with third cranial nerve palsy and with medial rectus muscle rupture after endoscopic sinus surgery.@*RESULTS@#The mean follow-up duration was 42 ± 20 months (12–79 months). The mean age at surgery was 40 ± 19 years (7–65 years). Eleven patients underwent surgery for sixth cranial nerve palsy, six patients underwent surgery for third cranial nerve palsy, and three patients underwent surgery for medial rectus rupture after endoscopic sinus surgery. The mean horizontal deviation at the primary eye position was 58 ± 19 prism diopters before surgery and decreased to 14 ± 17 prism diopters at the final visit. The success rate at the last visit was 60%. The mean horizontal deviation at postoperative 1 year was 4 ± 9 prism diopters in the sixth nerve palsy group and 26 ± 16 prism diopters in the third nerve palsy group (p = 0.002). The success rate was 91% in the sixth nerve palsy group and 33% in the third nerve palsy group at postoperative 1 year (p = 0.017). There were no complications during surgery or anterior segment ischemia for any of the patients.@*CONCLUSIONS@#A muscle union procedure had good long-term surgical outcomes in patients with paralytic strabismus, especially in patients with sixth cranial nerve palsy. However, in the case of third cranial nerve palsy or rupture of the medial rectus muscle, the effects were limited.

Clinical Features of Acute Opthalmoplegia Associated with Anti-GQ1b Antibody

PURPOSE@#To investigate the clinical features of acute ophthalmoplegia associated with anti-GQ1b antibody in the Republic of Korea.@*METHODS@#From January 2011 to July 2018, we retrospectively reviewed the medical records of all patients who tested positive for anti-GQ1b antibody, and who had been concurrently diagnosed with acute ophthalmoplegia at a tertiary hospital in the Republic of Korea. Ophthalmic and neurological features were carefully reviewed. Laboratory results including ganglioside antibody panels and treatment outcomes were analyzed.@*RESULTS@#Thirty-three patients were enrolled in the study and 8 (24%) of them showed pure Miller-Fisher syndrome with all three cardinal symptoms of ophthalmoplegia, ataxia, and areflexia. One patient (3%) showed ophthalmoplegia, areflexia, and pharyngeal- cervical-brachial weakness without ataxia and 2 patients (6%) showed only ophthalmoplegia and pharyngeal-cervical- brachial weakness without ataxia and areflexia. Twenty-two patients (67%) showed only ophthalmoplegia without any other neurological symptom. Early immunosuppressant treatment was used to treat 17 patients, and observation only was conducted as the initial treatment for 16 patients (48.5%). Twenty-four patients (72.7%) showed improvement and 9 patients showed persistent strabismus and diplopia. The average duration until recovery was 2.52 ± 2.11 months.@*CONCLUSIONS@#The symptoms of acute ophthalmoplegia associated with anti-GQ1b antibody can manifest in various forms that overlap with clinical features of demyelinating neuropathy, so it is important to recognize such characteristics when treating acute ophthamoplegia.

Association of Optic Neuritis with Neuromyelitis Optica Spectrum Disorder and Multiple Sclerosis in Korea

PURPOSE: To describe the clinical characteristics and course of optic neuritis (ON) and its association with neuromyelitis optica spectrum disorder (NMOSD) and multiple sclerosis (MS) in Korea. METHODS: In this retrospective case series, 125 eyes of 91 Korean patients with ON were included. The medical documents of adult patients with ON were retrospectively reviewed. Patients were assigned into idiopathic ON, NMOSD, and MS groups according to the presence of an association with NMOSD or MS for subgroup analysis. Clinical characteristics, disease course, and visual and systemic prognosis were analyzed. RESULTS: During the mean follow-up of 3.7 years, 73 patients were diagnosed as idiopathic ON, 14 patients were diagnosed as NMOSD, and four patients developed definite MS. At the final visit, there were 13 (13%) eyes out of 100 eyes with idiopathic ON, nine (43%) eyes out of 21 eyes with NMOSD, and one (25%) eye out of four eyes with MS had a severe visual loss of 20 / 200 or less. The mean Expanded Disability Status Scale was 3.1 ± 1.5 in NMOSD and 1.8 ± 1.5 in the MS group at the final visit. In the NMOSD group, 50% of patients showed severe visual loss in at least one eye or were unable to ambulate without assistance at the final visit (5.3 ± 4.4 years after the initial episode of ON). CONCLUSIONS: Fourteen percent of patients showed positive results for NMO-immunoglobulin G test and 50% of patients with NMOSD showed a severe visual loss in at least one eye or were unable to ambulate without assistance. The proportion of MS was relatively low in Korean ON patients.

Initial Pattern of Optic Nerve Enhancement in Korean Patients with Unilateral Optic Neuritis

PURPOSE: The purpose of this study was to demonstrate whether the pattern of optic nerve enhancement in magnetic resonance imaging (MRI) can help to differentiate between idiopathic optic neuritis (ON), neuromyelitis optica (NMO), and multiple sclerosis (MS) in unilateral ON. METHODS: An MRI of the brain and orbits was obtained in patients with acute unilateral ON. Patients with ON were divided into three groups: NMO, MS, and idiopathic ON. The length and location of the abnormal optic nerve enhancement were compared for ON eyes with and without NMO or MS. The correlation between the pattern of optic nerve enhancement and the outcome of visual function was analyzed. RESULTS: Of the 36 patients with ON who underwent an MRI within 2 weeks of the onset, 19 were diagnosed with idiopathic ON, 9 with NMO, and 8 with MS. Enhancement of the optic nerve occurred in 21 patients (58.3%) and was limited to the orbital segment in 12 patients. Neither the length nor the location of the optic nerve enhancement was significantly correlated with visual functions other than contrast sensitivity or the diagnosis of idiopathic ON, MS, or NMO. Patients with greater extent of optic nerve sheath enhancement and more posterior segment involvement showed higher contrast sensitivity. CONCLUSIONS: Our data revealed that the pattern of optic nerve enhancement was not associated with diagnosis of idiopathic ON, NMO, or MS in Korean patients with unilateral ON. We believe further studies that include different ethnic groups will lead to a more definitive answer on this subject.

Ocular Manifestations of Pediatric Systemic Disease / 한양의대학술지

Pediatric diseases are important because diagnosis and care for these can be complex. Among them, specific diseases have been associated with ocular involvement. This review presents the ocular manifestations of various pediatric diseases relevant to the clinician. An array of ocular manifestations of hyperthyroidism, hypoparathyroidism, diabetes mellitus, porphyria, cystinosis, mucopolysaccharidosis, Wilson disease, juvenile idiopathic arthritis, systemic lupus erythematosus, Marfan syndrome, Weill-Marchesani syndrome are described. In this review we will review ocular manifestations of systemic pediatric diseases for comprehensive understanding of eye involvement. With this review, authors can recognize the ocular manifestations for diagnosis and management of pediatric systemic diseases.

The Changes in Myosin Heavy Chain Isoforms After Extraocular Muscle Recession in Rabbits

PURPOSE: To study the changes in the amount and isoform pattern of the myosin heavy chain (MyHC) in rabbit extraocular muscle (EOM) fibers after recession. METHODS: Sixteen New Zealand white rabbits were used. Recession surgery was performed on the right superior rectus (SR) muscle by 3 mm in eight rabbits, and performed by 8 mm in other eight rabbits. The left SR muscles were left intact as the control groups. The SR muscles in both eyes were harvested from two rabbits from each recession group at 3 days and 1, 2, and 4 weeks after surgery. The changes in MyHC amount and isoform pattern were analyzed by gel electrophoresis. RESULTS: Total MyHC content decreased from 1 week after surgery in the 3-mm recessed group and from 3 days in the 8-mm group. The type IIb MyHC (MyHCIIb) plus EOM-specific MyHC (MyHCeom) showed similar proportional changes to the total MyHC at the different time points after surgery. CONCLUSIONS: The fast MyHCIIb plus the superfast MyHCeom decreased after EOM recession, and these results appear to be related to the changes in the global layer rather than in the orbital one. This suggests that the global layer might be the fast and the superfast twitch portions of rabbit EOM, which perform the fast saccades in ocular movements.

The Changes in Myosin Heavy Chain Isoforms After Extraocular Muscle Recession in Rabbits

PURPOSE: To study the changes in the amount and isoform pattern of the myosin heavy chain (MyHC) in rabbit extraocular muscle (EOM) fibers after recession. METHODS: Sixteen New Zealand white rabbits were used. Recession surgery was performed on the right superior rectus (SR) muscle by 3 mm in eight rabbits, and performed by 8 mm in other eight rabbits. The left SR muscles were left intact as the control groups. The SR muscles in both eyes were harvested from two rabbits from each recession group at 3 days and 1, 2, and 4 weeks after surgery. The changes in MyHC amount and isoform pattern were analyzed by gel electrophoresis. RESULTS: Total MyHC content decreased from 1 week after surgery in the 3-mm recessed group and from 3 days in the 8-mm group. The type IIb MyHC (MyHCIIb) plus EOM-specific MyHC (MyHCeom) showed similar proportional changes to the total MyHC at the different time points after surgery. CONCLUSIONS: The fast MyHCIIb plus the superfast MyHCeom decreased after EOM recession, and these results appear to be related to the changes in the global layer rather than in the orbital one. This suggests that the global layer might be the fast and the superfast twitch portions of rabbit EOM, which perform the fast saccades in ocular movements.

Innervated Myotendinous Cylinders Alterations in Human Extraocular Muscles in Patients With Strabismus

PURPOSE: To analyze innervated myotendinous cylinders (IMCs) in the extraocular muscles (EOMs) of normal subjects and strabismic patients. METHODS: The rectus muscles of 37 subjects were analyzed. Distal myotendinous specimens were obtained from 3 normal subjects, 20 patients with acquired strabismus, 11 with infantile strabismus, and from 3 with congenital nystagmus, and were studied by using light microscopy. Some specimens (6 rectus muscles) were also examined by transmission electron microscopy. RESULTS: IMCs were found in the distal myotendinous regions of EOMs. The IMCs of patients with acquired strabismus showed no significant morphological alterations. However, significant IMCs alterations were observed at the distal myotendinous junction of patients with congenital strabismus and congenital nystagmus. CONCLUSIONS: This study supports the notion that IMCs in human EOMs function mainly as proprioceptors, along with effector properties, and a disturbance of ocular proprioceptors plays an important role in the pathogenesis of oculomotor disorder. We suggest that a proprioceptive feedback system should be stimulated and calibrated early in life for the development of binocular vision.

Effect of Age Wearing Prescription Glasses on Changes of Refractive Error in Accommodative Esotropia

PURPOSE: To evaluate the effect of age wearing prescription glasses on changes in refractive error in accommodative esotropia. METHODS: We retrospectively reviewed the charts of 63 patients with accommodative esotropia. The patients were divided into three groups according to their age when glasses were prescribed. Changes of the refractive error between the three groups were compared. RESULTS: The mean age at the first visit was 4.1+/-2.0 years and the mean follow-up period was 5.7+/-2.7 years. In children that began wearing glasses before two years of age, the spherical equivalent (SE) refractive error initially increased, peaked 2.5 years after starting to wear glasses, and slowly decreased thereafter. In children who started wearing glasses after two years but not before four years of age the SE refractive error increased and peaked 1.5 years after starting to wear glasses. For children who began wearing glasses after four years of age the SE refractive error increased and peaked after one year. Changes in the refractive error in the youngest age group were significantly different from the other two groups (p=0.064). CONCLUSIONS: The age when glasses are prescribed may influence normal emmetropization in accommodative esotropia. However, further studies with longer follow-ups will be needed to determine the effect of wearing glasses on the final SE refractive error.

Distribution of Myosin Heavy Chain Isoform in Human Extraocular Muscles

PURPOSE: To provide quantitative data on the distribution of MyHCeom and compare the proportion of myosin heavy chain (MyHC) isoforms between the central and peripheral regions of human extraocular muscles (EOMs). METHODS: Medial rectus, lateral rectus, superior rectus, inferior rectus, superior oblique, and inferior oblique muscle samples were taken from three men with brain death. To examine the longitudinal distribution of myosin isoforms, the muscles were divided into central and peripheral portions of equal length. Electrophoresis and densitometry were used to quantify the distribution of MyHC isoforms. RESULTS: Electrophoresis of whole-muscle extracts of sampled EOMs revealed four MyHC bands that were identified as MyHCI, MyHCeom, MyHCIIa, and MyHCIIx. The proportion of MyHCeom was higher in the central region, whereas the proportion of MyHCIIa was higher in the peripheral region. The relative proportions of MyHCI, MyHCeom, and MyHCIIa were not significantly different among the EOMs. There was a tendency for higher levels of MyHCIIx in the inferior rectus muscle. CONCLUSIONS: The proportion of MyHCeom was higher in the central region of human EOMs. Further studies are needed to investigate the consequences of this distributional difference on the function of EOMs.

Prevention and Treatment of School Myopia

Myopia is the most common refractive error throughout the world. Exact and relative etiologies of myopia have not been investigated in detail, although the high prevalence rate of myopia in school children has been well documented. Patients with myopia must endure the physical and financial burden of spectacles or contact lenses throughout their lives. The National Eye Institute estimated that the costs of refractive eye examinations amount to $1 billion annually, with another $1.5 billion spent on eyeglasses each year. The age of onset of myopia is frequently between 5 to 15 years. There has been a dramatic increase in the prevalence rates of myopia over the past decades in Korea and other parts of Asia. The prevalence rate was 8~15% in 1970s, 23% in 1980s, 38% in 1990s, and 46.2% in 2000s in Korean school children. The remarkable increase in Asian school children suggests that life style risk factors during the school periods may have a great impact on the development of school myopia and the overall population prevalence rate of myopia. Because the gene pool has not changed significantly over the past decades, the rapid increase of the prevalence rates of myopia has been attributed to increases in near-work activities and environmental factors. Atropine is effective in preventing myopia by a non-accommodative mechanism. Atropine is a broad-band muscarinic antagonist that binds to all five identified muscarinic receptors. Animal and clinical studies have shown that the M1-selective muscarinic antagonist, pirenzepine, is effective in reducing axial length enlargement and preventing myopia.

Causes and Natural Course of the Sixth Cranial Nerve Palsy

PURPOSE: To evaluate the causes and natural course of sixth nerve palsy. METHODS: The records of 37 patients with the sixth nerve palsy were reviewed to analyze the age of onset, etiology, angle of deviation, natural course of the palsy, and percentage of intervention. RESULTS: The mean age of onset was 38.3 (3~77) years old. Causes and associations were: head trauma (n=11, 30%), idiopathic cause (n=9, 24%), neoplasm (n=7, 19%), aneurysm (n=2, 5%), and others (n=8, 22%). Complete recovery was observed in 80% of patients with nonhemorrhagic trauma and 33.3% with hemorrhagic trauma; 78% of patients with idiopathic cause; and 42.9% of patients with neoplasm. CONCLUSIONS: Head trauma was the most common cause of the sixth nerve palsy. Spontaneous complete recovery was observed in 80% of nonhemorrhagic trauma and 78% of idiopathic cases.

The Natural Course of Strabismus associated with Thyroid Ophthalmopathy

PURPOSE: This study investigated the natural course of strabismus associated with thyroid ophthalmopathy. METHODS: A retrospective review was performed on the medical records of 31 patients with strabismus associated with thyroid ophthalmopathy who had been followed up for more than 6 months and had not received surgery. For the purpose of this study, a significant change of deviation angle was defined as more than 10 prism diopters in the primary position. RESULTS: Forty-two percent of patients showed a significant change in deviation angle during the observation period of 23.8+/-17.7 months. The direction of the change was vertical in 32%, horizontal in 3%, and vertical and horizontal in 6% of patients. A significant change of deviation angle developed in 30% of patients within 6 months from the initial ophthalmologic examination, in 24% between 6 and 12 months, and in 13% of patients between 12 and 18 months from the initial examination. CONCLUSIONS: Although the deviation angle of strabismus associated with thyroid ophthalmopathy tended to stabilize with time, it nonetheless was susceptible to change even 12 months after the initial ophthalmologic examination. In addition, a vertical change in the deviation angle was more frequent than a horizontal change.

The Clinical Feature and Surgical Outcome of Infantile Exotropia

PURPOSE: To investigate the clinical features and treatment of infantile exotropia which developed in the first year of life. METHODS: The medical records of infantile exotropia operated on in our hospital were reviewed for preoperative and postoperative deviation, cycloplegic refraction, Worth 4-dot test and Titmus stereo acuity test. RESULTS: Preoperative mean deviation was 37 prism diopters. The average post-operative follow-up period was 26.5 months (12~86 months). Twelve patients (71%) had successful horizontal alignment with final horizontal deviations of less than 8 prism diopters, and five patients were undercorrected between 10 and 20 prism diopters. None were overcorrected. Six patients (35%) had fusion at distance and near as well as stereoacuity of 200 seconds of arc or less. Both preoperative and postoperative associated anomalies were inferior oblique muscle overaction (35%), dissociated vertical deviation (18%), both inferior oblique muscle overaction and dissociated vertical deviation (18%), nystagmus (12%) and V-pattern (6%). CONCLUSION: Although infantile exotropia is rare, it has similarities to infantile esotropia. Infantile exotropia features a large-angle deviation, accompanied with inferior oblique muscle overaction and dissociated vertical deviation. After operation, no cases were overcorrected, while high levels of binocular function, and stereoacuity developed in some cases.

Histologic Analysis of the Myotoxic Change by Bupivacaine and Ricin mAb 35 on Extraocular Muscle in Rabbits

PURPOSE: To analyze the acute histologic change of extraocular muscles (EOM) induced by injection of bupivacaine or Ricin mAb 35. METHODS: The superior rectus and inferior rectus of white rabbits were injected with either bupivacaine (0.4 mg in 0.3ml) or Ricin mAb 35 (0.2 micro gram/kg in 0.3 ml). One, two, and four weeks after injection, the rectus muscles were harvested and the post-injection changes were histologically analyzed. RESULTS: Both the orbital and the global layers of EOM showed myotoxic changes induced by bupivacaine and Ricin mAb 35. However, the inflammation and destruction of myofiber by bupivacaine injection were localized to the injection site, whereas changes induced by Ricin mAb 35 were diffuse. Regenerating myofibers with a central nucleus were found at one week after myotoxin injection. Four weeks after injection, the acute changes induced by these two toxins were much recovered with prominent myofiber regeneration. Bupivacaine-induced myotoxic change was more prominent in the global layer in contrast to the more prominent damage in the orbital layer induced by Ricin mAb 35. CONCLUSIONS: We found that EOM have a superb ability to recover from the acute injury induced by bupivacaine or Ricin mAb 35 and that the two myotoxins cause unique damage including the predilection of muscle layers and the duration for which the damage persisted. Further investigation into the functional change during recovery from the myotoxin-induced injury of EOM is needed.

The Effect of Previous Orbital Decompression on Outcome of Strabismus Surgery in Patients with Thyroid Ophthalmopathy

PURPOSE: To determine the effect of prior orbital decompression on the outcome of strabismus surgery in patients with thyroid ophthalmopathy. METHODS: The medical records of patients operated on for strabismus related to thyroid ophthalmopathy were retrospectively reviewed RESULTS: Thirty patients were included in this study. Seventeen patients had previously undergone orbital decompression, thirteen patients had not. There was no significant difference between the two groups in the average angle of preoperative horizontal or vertical deviation, the average numbers of muscle operated on, the percentage of unidirectional surgery and the outcome of strabismus surgery. CONCLUSIONS: The previous orbital decompression surgery has no significant effect on the outcome of strabismus surgery in patients with thyroid ophthalmopathy.

The Changes of Myosin Heavy Chain Isoforms after Tenotomy on Extraocular Muscle Layers of Rabbits

PURPOSE: Extraocular muscle (EOM) consists of two layers, the global and the orbital layer, which are readily distinguished by their histopathology. This study was conducted to investigate the changes of myosin heavy chain (MHC) and MHC isoforms of the global and the orbital layers of EOM after tenotomy. METHODS: Twenty four New Zealand white rabbits were used. The rectus muscles were harvested on day 3, week 1, week 2, week 3, week 4, and week 8 after EOM tenotomy. The change of MHC amount was measured using an electrophoresis. The changes of MHC isoforms were also measured quantitatively using western blot immunostaining. RESULTS: The amount of total MHC, fast MHC isoform, and slow MHC isoform decreased maximally at 1-week after EOM tenotomy and recovered at 4-week and 8-week after tenotomy. There was no significant change in the amount of the neonatal and developmental MHC isoform. CONCLUSIONS: Fast and slow MHC isoform changed mainly due to the changes in the global layer rather than in the orbital layer after EOM tenotomy.

Long-Term Outcome of Patients with Partially Accommodative Esotropia Who had Augmented Surgery

PURPOSE: To investigate the long-term outcome of patients with partially accommodative esotropia who had augmented surgery. METHODS: Twenty patients with partially accommodative esotropia who underwent augmented surgery were studied retrospectively. The amount of medial rectus recession was measured based on the average of the near deviation with and without spectacle correction. During the follow-up period, the changes of refractive error and angle of deviation were evaluated and the Titmus test and Worth 4-Dot test were performed. The follow-up period was at least 24 months. RESULTS: The average follow-up period was 51.6+/-18.16 months (28~86 months). Seventeen patients showed postoperative deviations of 10 PD or less, one patient was overcorrected, two patients were undercorrected. Sensory tests were performed in 17 patients. Worth 4-dot test resulted in a fusion response at far in 6 patients and at near in 8 patients. Titmus stereotest resulted in positive fly (3000 seconds of arc) in all patients and more than 80 seconds of arc in 3 patients. CONCLUSIONS: Surgical overcorrection in patients with partially accommodative esotropia who had augmented surgery is not worrisome and augmented surgery provides some degrees of stereoacuity and fusion.

The Change of Extraocular Muscle Layers After Tenotomy: Histologic and Immunohistochemical study

PURPOSE: Extraocular muscle (EOM) consists of two layers, orbital and global layers which are readily distinguished by their histology. This study was conducted to investigate the changes of histology, myosin heavy chain (MHC), and MHC isoforms of the global and orbital layers of EOM after tenotomy. METHODS: Forty-two New Zealand white rabbits were used. The rectus muscles were harvested at day 3, week 1, week 2, week 4, and week 8 after EOM tenotomy. EOM mass change was measured. The EOM were serially sectioned in coronal plane and stained with Masson's trichrome. The diameters of muscle fibers and cross sectional areas of two layers were measured in the middle of the muscles. Changes of MHC isoforms were also measured using immunohistochemistry. RESULTS: The EOM mass was decreased at all periods of surgery especially at day 3 and week 1, increased maximally at week 8. The diameters of EOM fibers in global layer were decreased at day 3, week 1, and week 2 after EOM tenotomy and increased maximally at week 8. The immunohistochemical stains of fast and slow MHC were weakened in the global layer at week 1 after tenotomy. CONCLUSIONS: EOM changes due to atrophy appeared at day 3, week 1, and week 2 after EOM tenotomy while EOM atrophy was recovered at week 4 and week 8 after the surgery. These changes did not appear on the EOM orbital layer but was shown in EOM global layer. These results were due to the histological and functional differences between the EOM global and orbital layers.