Transactions 29th European Strabismological Association Meeting – de Faber (ed) © 2005 European Strabismological Association, ISBN 04 1537 211 9

Etiology of paralytic strabismus

N. Sefi Yurdakul, S. Ugurlu, G. Aydeniz & A. Maden

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Atatürk Education and Research Hospital, I zmir, Turkey

ABSTRACT:

Purpose: To evaluate the etiologies and clinical features of patients with paralytic strabismus. Methods: The records of the patients followed with the diagnosis of paralytic strabismus were studied retrospectively.

Results: Of 122 patients, 53 were women (43%), 69 were men (57%), and the average age was 32.1 23.8 years (range, 1–80 years). Abducens nerve palsy was determined in 47 (38.5%), trochlear in 36 (29.5%), oculomotor in 31 (25.4%) and multiple nerve palsies in 8 patients (6.6%). Etiologies were congenital in 39 (31.9%), trauma in 34 (27.9%), vascular in 20 (16.4%), undetermined in 13 (10.7%) and other causes in 16 cases (13.1%). The most commonly affected nerve was trochlear (p 0.000) in the pediatric group and abducens (p 0.006) in the adult group.

Conclusion: Congenital and vascular diseases are the major causes of paralytic strabismus in childhood and adulthood, respectively. Each patient with paralytic strabismus should undergo appropriate investigation after a complete neuro-ophthalmologic examination.

1INTRODUCTION

Paralytic strabismus appears secondary to lesions that involve the muscle, neuromuscular junction, peripheral nerve, nuclear or supranuclear pathways (von Noorden & Campos 2002). Information regarding the etiology is of utmost importance in acquired paralytic strabismus as it will aid both diagnosis and management. In the current study, we have evaluated patients with paralytic strabismus retrospectively, and analyzed the findings in the adult and the pediatric population.

2MATERIAL AND METHODS

The records of patients followed with the diagnosis of paralytic strabismus between August 1999–December 2003 were studied retrospectively. Patients with strabismus secondary to restrictive or myopathic causes were not included in the study. Patient charts were reviewed to identify features of orthophtic, neuroophthalmologic and systemic evaluations as well as imaging studies. Patients were classified according to the type of nerve palsies and the etiology. Time of detection of motor nerve palsy was used to describe patients with pediatric onset (age 18 years) and with adult onset (age 18 years). If paralytic strabismus was noted since birth, it was classified as congenital; those with no clear etiologic reason were grouped as undetermined. Statistical analysis was carried out by SPSS version 10.0 (SPSS Inc., Chicago, IL) using chi-square test. P value below 0.05 was considered significant.

3RESULTS

Of the 122 patients with paralytic strabismus 53 were women (43%), 69 were men (57%), and the average age of was 32.1 23.8 years (range, 1–80 years). Abducens nerve palsy was determined

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Table 1. Distribution of etiology of paralytic strabismus in the pediatric group.

Table 2. Distribution of etiology of paralytic strabismus in the adult group.

in 47 (38.5%), trochlear in 36 (29.5%), oculomotor in 31 (25.4%), and multiple nerve palsies in 8 patients (6.6%). Etiologies were congenital in 39 cases (31.9%), trauma in 34 cases (27.9%), vascular in 20 cases (16.4%), and undetermined reasons in 13 cases (10.7%). Other causes such as meningitis-encephalitis (n 4), intracranial intervention (n 3), cavernous sinus lesions (n 2), multiple sclerosis (n 2), intracranial neoplasm (n 3), aneurysm (n 1) and arachnoid cyst (n 1) were noted in 16 cases (13.1%).

Distribution of etiologies are given in Tables 1 and 2 for pediatric and adult patients, respectively. Trochlear nerve palsy and congenital palsies were more frequent in the pediatric population (p 0.000). Abducens nerve palsy (p 0.006) and vascular factors (p 0.000) were more prevalent in the adult patient.

4DISCUSSION

Despite ample data, there is no consensus on frequencies of cranial nerve palsies leading to paralytic strabismus. In several studies, abducens nerve palsy was reported to be the most frequently observed palsy, followed by oculomotor and trochlear nerve palsy. The convoluted, lengthy course of abducens nerve was felt to be the reason of frequent involvement (Rucker 1966, Rush & Young 1981, Richards et al. 1992). On the other hand, von Noorden et al. (1986) reported that trochlear nerve palsy was the most frequent cranial nerve palsy, followed in decreasing order of frequency by abducens and oculomotor nerve palsies. In the current study, abducens nerve palsy was the leading palsy followed trochlear, oculomotor and multiple nerve palsies in decreasing order of frequency when all the patients were considered.

Comparison of frequencies of cranial nerve palsies according to the age of presentation has shown conflicting results. Kodsi & Young (1992) reported acquired abducens cranial nerve palsies significantly more often in the pediatric population and acquired trochlear cranial nerve palsies in the adult population. The proportions of cases involving acquired oculomotor cranial nerve palsies in the pediatric group were similar to those in the adult population. In contrast, in the current study, comparison of pediatric and adult groups yielded trochlear nerve palsy and abducens nerve palsy as the major causes of paralytic strabismus, respectively. With elimination of the congenital strabismus cases, abducens nerve palsy became the most frequent palsy in both groups.

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Previous studies have revealed different etiology as the major causes of paralytic strabismus in pediatric and adult populations. The microvascular diseases like hypertension, diabetes mellitus and atherosclerosis are known to be more prevalent in the elderly patients (Rush & Younge 1981). Berlit (1991) reported microvascular diseases to be the most frequent cause in patients older than 14 years. Similar results were observed in the current study. Patients above 18 years suffered from microvascular diseases; patients below 18 years had congenital nerve palsies and palsies secondary to trauma.

Trauma was reported to be the most frequent reason for acquired cranial nerve palsy in the pediatric patients (Kodsi & Young 1992). In the current study exclusion of cases with congenital origin resulted in a similar outcome; acquired palsies were of traumatic origin in the majority of the pediatric patients. It was the second commonest reason in adult patients, too. In our study group, trauma appears to play a significant role which may be attributed to high prevalence of both traffic and occupational accidents in Turkey.

Undetermined reasons have been reported to be the leading reason in paralytic strabismus in some studies among adult patients (Rush & Young 1981, Richards et al. 1992). This was not the finding in the current study, yet, this group was statistically significantly more prevalent in the adult group compared to the pediatric group. Undetermined reasons are felt to be composed of diseases associated with microvascular diseases that cannot be diagnosed with certainity. With progress in the currently available diagnostic methods, those that have been described as undetermined would probably decrease over the years.

In this study several other intracranial diseases were observed to cause cranial nerve palsy both in the adult and the pediatric patients which were classified as ‘others’. Advanced imaging techniques and detailed neurologic examination are to be performed depending on the clinical features of acquired paralytic strabismus so as to identify the specific intracranial diseases.

5CONCLUSION

Different outcomes regarding frequencies and etiology of paralytic strabismus in various studies are reported. The variable outcome might be attributed to different patient populations that have been studied, and to different study settings. Regardless of the relative frequency of any cranial nerve palsy, each patient with paralytic strabismus should undergo appropriate investigations including a complete neuro-ophthalmologic examination.

REFERENCES

Berlit P. 1991. Isolated and combined pareses of cranial nerves III, IV and VI. A retrospective study of 412 patients. J Neurol Sci 103: 10–15.

Noorden GK von, Murray E & Wong SY. 1986. Superior oblique paralysis. A review of 270 cases. Arch Ophthalmol 104: 1771–1776.

Noorden GK von & Campos EC. 2002. Paralytic strabismus. In Binocular vision and ocular motility. Theory and management of strabismus. 6th ed. St. Louis: Mosby: 414–457.

Kodsi SR & Younge BR. 1992. Acquired oculomotor, trochlear, and abducent cranial nerve palsies in pediatric patients. Am J Ophthalmol 114: 568–574.

Rucker CW. 1966. The causes of paralysis of the third, fourth and sixth cranial nerves. Am J Ophthalmol 61: 1293–1298.

Rush JA & Younge BR. 1981. Paralysis of cranial nerves III, IV, and VI. Cause and prognosis in 1,000 cases. Arch Ophthalmol 99: 76–79.

Richards BW, Jones FR Jr & Younge BR. 1992. Causes and prognosis in 4,278 cases of paralysis of the oculomotor, trochlear, and abducens cranial nerves. Am J Ophthalmol 113: 489–496.

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Transactions 29th European Strabismological Association Meeting – de Faber (ed) © 2005 European Strabismological Association, ISBN 04 1537 211 9

Clinical, pedigree and genetic analysis of congenital fibrosis of extraocular muscles

B.T. Öztürk*, E.C. Sener¸ & A.S¸. Sanaç¸

Hacettepe University, Faculty of Medicine, Department of Ophthalmology, Ankara, Turkey * Currently assigned at the Ankara Güven Hospital

N. Akarsu

Pediatrics, Hacettepe University Medical Faculty, Ankara, Turkey

K. Yamada & E.C. Engle

Division of Genetics, Children’s Hospital Boston and Harvard Medical School, Boston, MA, USA

ABSTRACT: Our study aimed to investigate the clinical characteristics and genotyping of CFEOM in the Turkish population. During a period of 10 years (1993–2003) 56 cases with CFEOM were followed at one university hospital setting. Three of these families and 4 of the sporadic cases were genetically analysed. We demonstrated that a CFEOM2 individual reduced to homozygosity across the CFEOM2 locus and harbored a homozygous mutation in PHOX2A. One CFEOM1 family was consistent with linkage to both CFEOM1 and CFEOM3 loci and the affected individuals had a pathogenic heterozygous mutation in KIF21A. In addition, we identified that one CFEOM3 pedigree was linked to the CFEOM1 locus and the affected individuals harbored another KIF21A mutation. The clinical and genetical analysis of the CFEOM patients reveals a complex disease condition in which further information may bring better treatment hope for the severely affected individuals.

1OBJECTIVE

CFEOM is an ocular motility disorder characterized by ptosis and restrictive ophthalmoplegia in the oculomotor and trochlear nerve distribution. Three genetic loci for CFEOM have been identified (CFEOM1–3) already which lead to a new classification of the disease which combines both genetic etiology and clinical presentation (Engle, 1995; Wang, 1998; Doberty, 1999; Engle, 2002). Our study aimed to investigate the clinical characteristics and genotyping of CFEOM in the turkish population.

2MATERIAL AND METHOD

During a period of 10 years (1993–2003) 56 cases (29 male, 27 female) with CFEOM were followed at one university hospital setting. The age of the patients at the time of the study ranged between 6 months and 74 years. Following the selection of the index cases from the charts, pedigree analysis and sample collection were prospectively carried out in the field. Genetic analysis was completed when possible.

3RESULTS

3.1Clinical Findings

In primary position, the affected eye was hypotropic in 69.6% of cases, associated with esotropia in 25% and exotropia in 19.6%. Clinical findings of 46.4% of participants were consistent with

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Figure 1. Photographs of a classic CFEOM case from pedigree 1.

Figure 2. Photographs of an individual from pedigree 1 showing variations from classical CFEOM.

that described for classic CFEOM (Figure 1). The restrictive strabismus can be very mild to very severe in the same family (Figures 1, 2). Amblyopia was noted in 95% and ptosis in 83.9% of the CFEOM cases. Associated ocular anomalies included nystagmus, microcoria, situs inversus, tilted disc, increased cupping and systemic anomalies included corpus callosum agenesis, sensorineural hearing deficit and facial paralysis.

3.2Pedigree analysis

Thirteen of the CFEOM cases were sporadic and the remaining 43 belonged to 6 families. Pedigree 1 (Figure 1) consists of 94 individuals 29 of which were affected by the disease. This pedigree presents autosomal dominant trait with variable expressivity (S¸ener, 2000). In 18 of affected members the phenotypic expression of the disorder is consistent with that described for classic CFEOM. The remaining 11 affected members had more variable clinical phenotypes that did not meet CFEOM1 criteria and so the pedigree was classified as CFEOM3. Pedigree 2 and 4 showed autosomal dominant trait with classic CFEOM1 patients. Pedigree 3, 5 and 6 presents features of CFEOM3 as the affected members presents findings variable from classic CFEOM.

3.3Genetic Analysis

Three of these families and 4 of the sporadic cases were genetically analysed (Table 1). We demonstrated that one of our sporadic CFEOM2 individual (Case1) reduced to homozygosity across the CFEOM2 locus and harbored a homozygous mutation in ARIX (PHOX2A) (Nakano, 2001). The CFEOM1 family (Pedigree 2) was consistent with linkage to both CFEOM1 and CFEOM3 loci and the affected individuals had a pathogenic heterozygous mutation in KIF21A (Yamada, 2003). In addition, we identified that the CFEOM3 family in pedigree 1 was linked to the CFEOM1 locus and the affected individuals harbored another KIF21A mutation (¸Sener, 2000; Yamada, 2004).

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Figure 3. Pedigrees of Turkish CFEOM families.

Table 1. Results of genetic analysis.

L: linked; cw: consistent with linkage; rp: reduced penetrance.

4CONCLUSIONS

CFEOM is one of the rare inherited ocular motility disorders. As the genetic basis of the disease becomes known the way it is being classified is changing. Studies led to definiton of three genetic loci (CFEOM1-3) and three phenotypes arranged according to these genetic loci (Engle, 2002). The

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findings that CFEOM1 results from a primary absence of the superior division of the oculomotor nerve and that affected patients harbor mutations in KIF21A and that CFEOM2 results from absence of the oculomotor and trochlear nuclei and that affected patients harbor mutations in ARIX ( PHOX2A) provide insight that has allowed these disorder to be classified as neurogenic rather than myopathic (Yamada, 2004). Genetic analysis of several of the Turkish CFEOM pedigrees revealed mutations both of these genes and supports this hypothesis (Nakano, 2001; Yamada, 2003). The clinical and genetical analysis of the CFEOM patients reveals a complex disease condition in which further information may bring better treatment hope for the severely affected individuals.

REFERENCES

Doberty E.J. 1999. CFEOM 3: A new extraocular congenital fibrosis syndrome that maps to 16q24.2–24.3.

Inves Ophthalmol Vis Sci 40(8):1691–4.

Engle E.C. 1995. Congenital fibrosis of the extraocular muscles (Autosomal dominant congenital external ophthalmolplegia): Genetic homogeneity, linkage refinement and physical mapping on chromosome 12.

Am J Hum Genet 57:1086–94.

Engle E.C. 1997. Oculomotor nerve and muscle abnormalities in congenital fibrosis of the extraocular muscles. Ann Neurol 41:314–25.

Engle E. 2002. The molecular basis of the congenital fibrosis syndrome. Strabismus 10(2): 125–8.

Nakano M. 2001. Homozygous Mutations in ARIX(PHOX2A) result in congenital fibrosis of the extraocular muscles type 2. Nat Genet 29:315–20

Sener¸ E.C. 2000 A Clinically Variant Fibrosis Syndrome in a Turkish Family Maps to the CFEOM1 Locus on Chromosome 12. Arch Ophthalmol 118:1090–97.

Wang S.M. 1998. Congenital fibrosis of the extraocular muscles type 2, an inherited exotropic strabismus fixus, maps to distal 11q13. Am J Hum Genet 63:517–25.

Yamada K. 2003. Heterozygous mutations of the kinesin KIF21A in congenital fibrosis of the extraocular muscles type 1 (CFEOM1). Nat Genet. 35:318–21.

Yamada K., 2004. KIF21A mutations are a rare cause of congenital fibrosis of the extraocular muscles Type 3 (CFEOM3). Invest Ophthalmol Vis Sci. [in press]

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Transactions 29th European Strabismological Association Meeting – de Faber (ed) © 2005 European Strabismological Association, ISBN 04 1537 211 9

Abnormal lateral rectus insertion associated with V-pattern exotropia and up-shoot

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Y. Uysal, F.M. Mutlu, C. Erdurman, H.I Altınsoy S.M.Z. Bayraktar

GATA Department of Ophthalmology, Ankara, Turkey

D. Ceyhan

Gendarmerie Military Hospital, Ankara, Turkey

ABSTRACT:

Purpose: To report the clinical characteristics, preoperative, intraoperative, postoperative, anatomic findings of four cases of V-pattern exotropia, with up-shoot in one eye and inferior oblique over-action in the other eye.

Materials and Methods: We reviewed retrospectively the data of four patients who had V-pattern exotropia and up-shoot with abnormal lateral rectus insertion. All four patients underwent strabismus surgery and inferior oblique myectomy and lateral rectus recession procedures were performed.

Results: Mean age was 22.2 (ranged from 21 to 23) years. There was exotropia and up-shoot in all patients. During the operation, we observed that lateral rectus muscles inserted posterior and inferior of the expected insertion site of the eye with up-shoot and also extended from posterior and inferior part of the orbit. After the operation in all patients, substantial decrease in up-shoot was obtained and exotropia was decreased to less than 10 prism diopter.

Conclusion: In cases with both V-pattern and up-shoot, the abnormal insertion of the lateral rectus muscles should be considered during the operation planning phase. MRI scan focusing on the extraocular muscles may be beneficiary.

1INTRODUCTION

Up-shoot is the elevation of the eye during adduction (strabismus sursoadductorius). Patients with up-shoot complain about the disappearance of the eye during inward movement. There is also loss of fusion during side gaze, which may cause functional impairment. This clinical entity is mostly seen with Duane’s syndrome. It is also seen with exotropia (XT), esotropia (ET) and as an isolated clinical picture. If it is with exotropia, there is usually V-pattern strabismus (von Norden, 1996a).

V-pattern XT constitutes 23–30% of all A- and V-pattern strabismus cases (Rosenbaum). It is not usual to see cases with both up-shoot and V-pattern. The co-existance of V-pattern and up-shoot is a challenging problem to the clinician, regarding the etiology and treatment of these cases, and the existance of abnormal muscle insertions have been rarely reported (Lee, 1996).

We present clinical, preoperative, operative, and post-operative findings of 4 cases of V-pattern XT, with up-shoot in one eye, and propose a possible embryologic explanation to these cases.

2REPORT OF CASES

Case 1: 23 years old male patient complains about outward turning of his eyes. In examination visual acuity was 20/20 in both eyes and there was an XT of 40 prism diopter (pD) with V-pattern. Although he was not much concerned, his right eye (RE) was up-shooting during left gaze. Also

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there was a slight up-shoot of his left eye. We thought that IO (inferior oblique) OA (over acting) contributes to the up-shoot of the eye. Bilateral IO myectomy and bilateral lateral rectus (LR) 7 mm recession, RE adjustable, was planned.

First, LE was operated. After, IO myectomy of the right eye was completed, and we observed that the lateral rectus of the RE (the eye with more up-shoot) inserted posterior and inferior of the expected insertion site. Also the LR muscle was extending from the posterior inferior part of the orbit. The insertions of inferior and superior rectus were normal. Lateral rectus was supraplaced and sutured beyond the expected insertion site, measuring from limbus. During the first postoperative day there was an 18 pD of XT and no up-shoot and IOOA. After 6 weeks the XT became an XT of 20 pD. The patient has undergone resection of 5.5 mm of both medial recti. After this operation patient has an XT of 8 pD and no up-shoot or IO OA.

Case 2: The second case had almost the same findings preoperatively. A V-pattern XT of 35 pD and up-shoot of the right and a slight up-shoot of the left eye. The operation plan was bilateral inferior oblique myectomy and bilateral lateral rectus recessions of 6.5 mm.

During the operation it was observed that, the lateral rectus of the right eye inserted posterior and inferior of the expected insertion site. Like previous case the muscle was also extending from inferior and posterior of the orbit. Other operated muscles and the inferior rectus insertion site were normal. The LR was reattached beyond the expected insertion site, measuring from the limbus. After the operation there was an XT of 10 pD and, a substantial decrease in up-shoot and IO OA

Case 3: This case is 23 years old and complains about the outward turning of his eyes. He had an alternating XT of 20 pD and a V-pattern strabismus. His left eye was elevating during inward movement; also right eye was elevating slightly during adduction. First, IO muscle of both eyes were disinserted, and the LR of the left eye planned to be recessed 6 mm. During the operation LR was seen to insert inferior and posterior of expected insertion site. This muscle was supraplaced and reattached behind the expected insertion site. Also this muscle was stitched to sclera 4 mm posterior of new insertion site. After the operation there was a 5 pD of XT and there was a decrease of the up-shoot of both eyes.

Case 4: 21 years old male patient complains about outward turning of his eyes. A V-pattern XT of 20 pD, dissociated vertical deviation (DVD) of the left eye together with up-shoot and ( ) 4 IO OA, and ( ) 1 OA of the right IO muscle. First, anterior transposition of the left IO muscle was performed then LR was seen to insert inferior and posterior of expected insertion site. This muscle was supraplaced and reattached 7 mm behind the expected insertion site. Also this muscle was stitched to sclera 4 mm posterior of new insertion site. After the operation there was a 5 pD of XT and there was a decrease of the up-shoot of left eye, and a significant decrease of V-pattern and DVD.

3DISCUSSION

Regarding the etiology of V-pattern strabismus, there are excellent reviews discussing the possible effects of horizontal, vertical, oblique muscles or anomalies of muscle insertions and orbital structural differences (Von Norden, 1996b; Von Norden, 1986; Kushner, 1991). There should be no single etiologic factor causing these complex clinical pictures.

In our cases, it is hard to propose a relationship between abnormal insertion of lateral rectus in one eye and the existence of V-pattern. We did not see an abnormal insertion of the lateral rectus of the eye without up-shoot. So, abnormal lateral rectus insertion may be only a contributing factor to V-pattern, not the major cause of the entity. The abnormal insertion may be the only detectable part of a more generalized sub-clinical abnormality of orbital contents, resulting both V-pattern exotropia and the elevation during inward gaze.

Up-shoot is mostly studied with Duane’s Syndrome. The possible etiologic factors are reviewed in some reports (Von Norden,1986). It is usually believed to be the result of the:

a)Spasmodic contraction of the inferior oblique;

b)Paradoxical synergistic innervations between medial and superior rectus muscles;

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c)A bridle effect of two horizontal muscles; proposing that as the muscle planes change, the horizontal muscles become elevators, and up-shoots the eye.

Regarding the findings of versions; in the cases with up-shoot, the effect of inferior oblique muscles is the first to be considered. The unsuccessful results of inferior oblique surgery with upshoot in Duane’s syndrome showed the need for another explanation. In our cases we observed that the IO surgery together with LR recession decreased the up-shoot of in both eyes. IO muscle maybe caused at least a limited effect on elevation during adduction (up-shoot) of eyes, but it is speculative without any evidence except abnormal LR insertion.

Kuschner (1991) reported that in V- and Y-pattern strabismus, some hypertropia during adduction might be confused with IO OA. He proposes that IO OA appears during whole adduction, pseudo IO OA occurs only when the eye goes up over the horizontal level. He also proposes that this kind of movement may be a form of co-contraction abnormality. Although there should be some effect of IO on the over elevation of our cases, supraplacing the lateral rectus, that inferiorly located, has a relieving effect for up-shoot too. We believe that the abnormal insertion of LR has more effect on up-shoot of these eyes, because over elevation of the eyes with abnormal insertion was marked.

Jampolsky reported that the all the knife-edge up-shoot was always related to abnormal mechanics or structure of lateral rectus muscle (Jampolsky, 1999). We think the up-shoot of the eyes of our cases should be the result of the abnormal insertion of the lateral rectus. There was not any other anatomic finding that explain the up-shoot of the eye, nor an abnormal insertion of the lateral rectus in eyes without up-shoot. We could not recognize abnormal lateral rectus insertion in eyes with slighter up-shoot. There may be an undetectable insertion abnormality of the lateral rectus of these eyes.

More recently, “muscle pulleys” and extraocular muscles’ relation with these pulleys and the effect of these structures on strabismus have been studied (Demer, 2002b). Heterotopy of rectus pulleys was reported to be the cause of some incomitant cases. Demer (2002a) reports that the inferior location of lateral, relative to medial rectus pulley causes the medial rectus act as a relative elevator in adduction. The “heterotopy” of LR of our cases may cause over-elevation in adduction. According to our findings, this, like bridle theory, accounts to be the most relevant explanation of the up-shoot of the cases (Von Norden,1986). This muscle should become an elevator, when the muscle planes change during inward movement. We used a posteior fixation suture to pull the muscle horizontal plane but we could not observed clinically significant difference with respect to the cases without posterior fixation suture. Also the effect of over-acting IO may augment the elevator effect of the abnormally inserted LR.

It is hard to predict the total effect of the abnormal insertion site of LR about the etiology of V-pattern and up-shoot according to our findings. We believe that, the abnormal insertion of lateral rectus should be the only visually detectable pathology in orbital contents, causing this clinical picture. Some sub-clinical differences should contribute to the existence of the whole findings.

Embryologically, the extraocular muscles develops as condensations in the paraxial mesoderm surrounding the optic vesicle (Mann,1964). While the muscles differentiate from the apex of the orbit forward, the sclera simultaneously differentiates in the opposite direction (Jacobiec, 1982). The muscles that innervated by different nerves have different embryological origins. The muscles innervated by III nerve derives from premandibular condensations; and the lateral rectus derive from the tissues adjacent to maxillomandibular mesoderm. The nerves of these muscles develop at different weeks of fetal development. Also the collagen fibers enveloping muscles and connective tissue septa develop after the muscles.

The abnormal insertion of these muscles may be the result of an embryological insult during development of these particular parts, at their particular development time. The co-existence of craniofacial dysostosis and extraocular muscle insertion abnormalities are reported; and also coexistence of heterotopias of extraocular muscles with facial asymmetry is reported (Coats, 2000). We propose that, cases like ours are a slight form of the cases with craniofacial anomalies, which frequently co-exist with muscle abnormalities. The existence of facial asymmetry should be a warning sign for the clinician, for muscle abnormalities, during treatment planning phase.

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Although a detailed oculomotor evaluation is performed, the exact cause of up-shoot and V-pattern could not be understood clearly. Before deciding to operate on certain muscles, all possible etiologic factors should be thought and the surgeon should be ready to change the operation plan. In cases with both V-pattern and upshoot, the abnormal insertion of the lateral rectus muscles should be considered, during the operation-planning phase. If it is possible an MRI scan focusing on the extraocular muscles may be beneficiary.

REFERENCES

Coats D.K. et al. 2000. Surgical management of V-pattern strabismus and oblique dysfunction in craniofacial dysostosis, JAAPOS 4:338–421.

Demer J.L.2002. Behind the insertions: New concepts of extraocular muscles for orbital and strabismus surgeons, AAO/PAAO joint Meeting Orlando.

Demer J.L. et al. 2002. A 12-year, prospective study of extraocular muscle imaging in complex strabismus. JAAPOS 6:337–347.

Jacobiec F.A. 1982. Ocular anatomy embryology and teratology, Philadelphia, Harper & Row Publishers. p. 783. Jampolsky A. 1999. Duane syndrome In A.L. Rosenbaum & A.P. Santiago (eds), Clinical strabismus

management: 326–344. Philadelphia, W.B. Saunders Co. p.335.

Kushner B.J.1991. Pseudo inferior overaction associated with Y- and V-patterns Ophthalmol. Oct 98: 10: 1500–1505.

Lee J.P. 1992. Congenital extraocular muscle defects, Eye 6: 181–183.

Mann I. 1964. The development of the human eye, New York, Grune & Stratton Inc. p.256.

Von Noorden G.K & Murray E.1986 Upand downshoot in Duane’s retraction syndrome JPOS 23: 212–215. Von Noorden Gunter K. Up-shoot in adduction 1996a. Binocular Vision and Ocular Motility 5th Ed. Mosby

Year Book Inc. p.367–368.

Von Noorden Gunter K Binocular Vision and Ocular Motility 5th Ed. Mosby-Year Book Inc. 1996 A- and V-patterns p.376–391.

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