Strabismic Complications Following Endoscopic Sinus Surgery: Diagnosis and Surgical Management

Transcription

1 Strabismic Complications Following Endoscopic Sinus Surgery: Diagnosis and Surgical Management Neepa M. Thacker, MD, a Federico G. Velez, MD, a Joseph L. Demer, MD, PhD, a,b Arthur L. Rosenbaum, MD a Introduction: Endoscopic surgical techniques improve the surgeon s view of sinus structures but are subject to extraocular muscle complications that cause permanent diplopia. Methods: A series of 15 patients with strabismus following endoscopic sinus surgery was reviewed retrospectively to characterize the type of muscle injury and report the results of surgical correction. Results: A variety of insults to the medial rectus (MR) muscle occurred, ranging from contusion, hematoma, oculomotor nerve damage with paralysis, muscle transection, and muscle destruction. Inferior rectus and superior oblique muscle trauma was observed. High-resolution computed tomography and magnetic resonance imaging scans proved essential in determining the extent and nature of muscle injury. Surgical approaches included anterior orbitotomy with muscle recovery and transposition procedures. Conclusions: Several extraocular muscles may be traumatized. Timing and type of surgical treatment depend on severity, type of injury, and number of muscles involved. If the remaining posterior segment of the MR muscle is longer than 20 mm and is contractile, muscle recovery via anterior orbital approach is suggested. If injury is more severe, muscle transposition procedures may be helpful. In cases where there is coexistent medial and inferior rectus injury, transposition procedures may not be possible. Inactivation of the antagonist and use of an orbital periosteal flap as a globe tether to center it may be options. (J AAPOS 2004;8: ) D uring the past decade, endoscopic techniques have been developed to improve the surgeon s view of sinus structures and to facilitate diagnosis and treatment of sinus diseases. 1 These new procedures entail risk of orbital and ocular complications if the orbit is entered. Endoscopic surgery undertaken by surgeons for chronic sinus disease is often complicated by the finding that the lamina papyracea separating the orbit from the sinus is either completely damaged or markedly attenuated because of the nature of the sinus disease. This and the very nature of the surgery, even with endoscopic visualization, is still fraught with risk. Reported orbital complications include periorbital ecchymosis, proptosis, retrobulbar hemorrhage, nasolacrimal duct injury, damage to the From the Jules Stein Eye Institute, Department of Ophthalmology, and Department of Neurology, University of California, Los Angeles, CA Presented at the Annual Meeting of the American Association for Pediatric Ophthalmology and Strabismus, Seattle, March 2002, under the title Strabismic Complications Following Endoscopic Sinus Surgery: Diagnosis and Surgical Management. Supported by core grant EY to the Department of Ophthalmology at the University of California, Los Angeles. Also supported by an unrestricted grant from Research to Prevent Blindness. Joseph L. Demer is Laraine and David Gerber Professor of Ophthalmology. Submitted October 18, Revision accepted September 2, Reprints requests: Arthur L. Rosenbaum, MD, Jules Stein Eye Institute, Loo Stein Plaza, UCLA, Los Angeles, CA rosenbaum@jsei.ucla.edu Copyright 2004 by the American Association for Pediatric Ophthalmology and Strabismus /2004/$ doi: /j.jaapos medial rectus (MR) muscle, and injury to the optic nerve. 2,3 Extraocular muscle damage may cause permanent strabismus with troublesome diplopia. The newer powered devices used for endoscopic sinus surgery reduce the risk of hemorrhage during sinus surgery but have a greater potential to damage extraocular muscles when accidentally misdirected. 4 The aim of this study was to characterize the type of muscle injury and report the results of surgical correction. METHODS This is a retrospective review of 15 referred cases over the 8-year period 1994 to 2002, who presented with strabismus as a complication of endoscopic sinus surgery. No patient in this series had history of strabismus or strabismus surgery prior to the endoscopic sinus surgery. Two patients (Case 4 and 7) in this series have been reported as parts of previous publications. 5,6 Each patient underwent a complete ophthalmic and ocular motility examination, including best-corrected visual acuity in each eye. Characteristics of any anomalous head position were measured with a goniometer as the patient read binocularly at distance and near. 7 Facial asymmetry or lid anomalies were noted. Strabismic deviation was measured in the six cardinal gaze positions as well as head tilts where appropriate. Versions were assessed in all nine gaze positions. Ocular torsion was measured subjectively using double Maddox rods and objectively by viewing the fundus with indirect 488 October 2004

2 Volume 8 Number 5 October ophthalmoscopy. Sensory status was evaluated with and without an abnormal head position using the Titmus fly stereo acuity test (Titmus Optical Co., Inc., Petersburg, VA) and/or the Worth four dot test (Western Ophthalmic Corp., Lynwood, WA). Forced duction and force generation tests were performed, as described, on all patients. 8 Topical anesthetic was applied to the eye being tested and the other eye was covered. The patient was instructed to look in the direction of suspected limited rotation. The examiner grasped the globe with a toothed forceps, as close to the limbus as possible opposite the side of gaze limitation. If the globe could not be passively rotated further than the patient s effort, restriction was diagnosed; if passive rotation was possible, paresis was diagnosed. The force generation test was performed concurrently with the forced duction test with the same grasp of the globe with the patient maintaining the same position. The examiner applied traction in the opposite direction and evaluated the resistance encountered. The forced generation test estimated muscle force and graded muscle function as normal, reduced (paretic muscle), or absent (palsied muscle). Saccadic velocity was observed clinically. The patient was asked to cover one eye and alternate gaze between two targets separated at least 20 degrees horizontally or vertically. Saccades were measured in gaze fields with an unrestricted range of movement. The briskness of the generated saccade was noted and the agonist and antagonist velocities and saccades from the fellow normal eye in the same direction were compared. Slow or floating saccades indicated muscle weakness. 9 Three of the 15 patients had a Hess screen test before and after surgery. Multipositional surface coil magnetic resonance imaging (MRI) of the orbits was performed in 14 of the 15 cases. A computed tomography (CT) and a MRI scan of the orbits done elsewhere was available with one patient and hence this was not repeated. Multipositional MRI scans of the orbits were obtained according to a previously described protocol. 10 Images were obtained by using target lights within the scanner to control gaze directions or by asking the patient to maintain a particular gaze position. Multiple positions, particularly the field of action of the muscle in interest and its opposite field of gaze, demonstrated the muscle contractility. Images were obtained with T1 weighting, 2- or 3-mm thickness at a pixel resolution of 312 to 390 urn. Axial, coronal, quasicoronal (perpendicular to the orbital axis), and sagittal views were obtained as needed. Iris angiography was performed in 6 of the 15 patients. These were patients who would require surgery on multiple rectus muscles of the injured eye. The surgical strategy in each case was individualized based on the nature of muscle injury, the time of presentation, and clinical picture at presentation and type of previous orbital and muscle surgery. When indicated, anterior orbitotomy with recovery of the functional muscle stump was performed with the assistance of an orbital surgeon. 5 The orbit was approached through a fornixbased transconjunctival incision. Dissection towards the orbital apex proceeded along the internal periosteal surface. The rectus muscle stump was identified and freed of adjacent scar tissue and a non-absorbable double-armed suture was placed through the edge. The muscle stump was advanced as far as possible anteriorly, without creating significant restriction to ocular rotation and sutured to the sclera. Full-tendon width rectus muscle transposition procedures were performed to replace function in the field of action of a totally destroyed or palsied muscle. 11 When full tendon-width vertical rectus muscle transpositions were performed to the medial rectus insertion, a 4-mm resection of each vertical rectus was added to reduce the created slack and enhance the effect. Augmentation with posterior fixation sutures as described by Foster 12 was also used to enhance the effect of the transposition. In cases with high risk of developing anterior segment ischemia or when the iris angiogram showed delayed iris filling or evidence of filling defects, ciliary vessel sparing full tendon-width transpositions or partial augmented vertical rectus transpositions were performed. In partial tendon-width vertical rectus muscle transposition procedure, the muscle was split in half from its insertion to 9 mm posteriorly, each half having its ciliary vessel branch. One-half of the split muscle was transposed to the desired insertion site. The other non-transposed half with its preserved ciliary vessel remained attached to its original insertion site. This procedure was performed to preserve patency of the anterior segment ciliary circulation and reduce the incidence of anterior segment ischemia. 13 Botulinum toxin (Allergan, Irvine, CA) was injected into the antagonist muscle during the recovery phase of a palsied muscle to prevent its contracture. In the office, 1.25 to 2.5 units of botulinum was injected transconjunctivally under electromyographic control into the muscle belly around the nerve muscle function. 14 Intraoperatively botulinum was injected under direct visualization about 6 to 8 mm from the insertion into the muscle belly, thus avoiding the tendon. RESULTS This is a retrospective review of 15 patients who sustained injury to the extraocular muscles or their nerves during endoscopic sinus surgery. We found a variety of insults to the extraocular muscles, ranging from contusion, hematoma, damage to the oculomotor nerve entry zone, or transection to complete destruction with entrapment in scar tissue. The type of endoscopic surgical procedure performed in each case, the extraocular muscles involved, and the corresponding injury are listed in Table 1. Seven of the 15 (46%) patients had injury to only one extraocular muscle, while 7 (46%) had injury to two muscles, and 1 (6%) patient had involvement of three muscles. The MR muscle was the most commonly involved (13 of 15 cases,

3 490 Volume 8 Number 5 October 2004 TABLE 1 Type of endoscopic sinus surgery, extraocular muscles involved, and type of injury Patient No. Type ESS EOM Damaged Nature of Injury 1 Unilateral ethmoidectomy MR Injury to nerve with muscle hematoma 2 No details MR Damage with muscle contusion 3 Bilateral ethmoidectomies MR Damage with incomplete destruction 4 No details MR Transection 5 Bilateral pasinusotomy* MR Damage with incomplete destruction 6 Bilateral pansinusotomy MR Transection Damage to nerve 7 Bilateral ethmoidectomies MR Transection Damage 8 Bilateral pansinusotomy MR Transection Contusion 9 Bilateral pansinusotomy MR Destruction Destruction 10 Bilateral maxillary antrostomies Destruction 11 No details MR Entrapment in bony defect Entrapment in bony defect 12 Bilateral pansinusotomy MR Destruction with entrapment in scar tissue Destruction with entrapment in scar tissue Contusion with mild damage 13 Bilateral pansinusotomy Mild damage with paresis 14 Bilateral pansinusotomy MR Injury to nerve, mild damage to post 1/3 Injury to nerve 15 Bilateral pansinusotomy MR Transection Mild damage with paresis ESS endoscopic sinus surgery; EOM extraocular muscle; inferior rectus muscle; MR medial rectus muscle; superior oblique muscle. *Represents sinus surgery on all three sinuses consisting of ethmoidectomy, sphenoidectomy, and maxillary antrostomy. Contusion injury of a muscle was defined as the muscle being as paretic; no anatomic abnormalities noted on MRI scans, and the muscle subsequently recovering its function. 86%). Interestingly, in addition to the MR, we also found various degrees of damage to the inferior rectus (; 7 of 15 cases, 46%) and superior oblique () muscles (4 of 15 cases, 26%). All patients had unilateral extraocular muscle damage, the right eye being more commonly involved (11 of 15 cases, 73%). Injury to the MR was most commonly associated with ethmoidectomy procedures. injury occurred when maxillary antrostomies were performed. Details of type of sinus surgery performed were not available in three patients. Details regarding the use of powered devices during the endoscopic procedures were not available except in two cases with severe muscle damage. One case resulted in total destruction of the MR and muscles, as shown by preoperative imaging. In the other case there was complete MR transection with loss of a large portion of the muscle. Four patients (Cases 3, 4, 6, and 7) had previous orbital and extraocular muscle surgery for this complication before they were referred to us. Their details are shown in Table 2. Orbital repair had been done for one patient for a cerebrospinal fluid (CSF) rhinorrhea (Case 7). Table 2 shows the preoperative alignment, imaging findings, previous surgeries if any, management strategies, and postoperative alignment of the patients. Preoperatively four patients had a normal head posture. In these patients the strabismic deviation was so large that they did not attempt to overcome it with a compensatory head posture. In the 15 patients, preoperative face turn ranged from 0 to 40 degrees (mean 14.5 degrees) and chin position ranged from 0 to 15 degrees (mean 6.6 degrees). Postoperatively the face turn ranged from 0 to 7 degrees (mean 2 degrees) (P 0.006) and the chin position ranged from 0 to 3 degrees (mean 1 degree) (P 0.1). Postoperatively eight of these patients had a normal head position and the other five had residual anomalous head posture of less than 7 degrees. Six of the 11 (Cases 3, 4, 5, 7, 8, and 12) (54%) patients who underwent surgery had preoperative iris angiography to determine the state of the anterior segment circulation. Five of these showed normally filling iris circulation and one patient (Case 4) showed delayed iris filling with filling defects in two quadrants. No surgical intervention was performed in two patients (13%). Three patients (20%) had an anterior orbitotomy to recover the functional muscle stump (20%). Five patients (33%) had transposition procedures to replace lost muscle function. One patient (6%) had an orbitotomy and a subsequent transposition procedure. One patient (6%) had an extirpation of the lateral rectus (LR) combined with a medial periosteal globe fixation procedure to center the globe. One patient (6%) had a recession of the contralateral to correct the hypertropia secondary to ipsilateral paresis (6%). Two patients (13%) presented recently and are awaiting management. Seven of the 11 patients (63%) who had surgical correction required two or more surgical procedures. In Cases 1 and 2 where the MR was intact but paretic due to contusion injury, no surgery was performed and the patients were observed. Case 1 had a mild contusion to the

4 Volume 8 Number 5 October TABLE 2 Preoperative alignment, findings on imaging, previous surgical procedures (if any), management strategies, and postoperative findings Patient No. Preop Dev MRI Findings 1 RXT-25 Hematoma MR, damage to nerve branch to MR, contusion injury MR Previous Procedures Surgery Postop Dev None Small XP 2 18 RXT, 3 LHT RMR intact but not contracting Botox RLR 4 XT P, 20 XT LG 3 20 RXT, 6 RHT Partial damage, thin filament in 1. RLR recess 1. Ant orbitotomy recovery of RMR 4XP continuity of RMR attachment to globe, RLR 4 12 RHT, 14 XT Stump of proximal LMR at 20 mm with some function 5 40 RXT Strand of RMR present along full length 6 50 RXT, RHT 4, excyclo Transection RMR, middle missing, 12-mm proximal stump 7 70 RXT, 12 RHT, excyclo 5 10-mm proximal RMR stump 8 50 RXT Transection MR, adhesion between MR stump and optic nerve rerecess 2. Partial TWT of 2. Rerecess RLR* RSR, R to RMR 1. Orbital 1. Ant orbitotomy, recovery, 12 EP exploration advancement LMR, botox LLR 2. Hummelsheim 2. Botox LLR twice 6 RHT 3. L recess 1. Ant orbitotomy recovery RMR, 20 XT post 7-mm stump found and attached to globe, Botox RLR 1. Orbital exploration 1. Orbital repair CSF leak 2. Partial aug transp with resec RSR, R to RMR, Botox RLR 1. Full-tendon augmented transposition with resection of RSR, R to RMR, botox RLR 8XT 2. RIO recess 2 RHT 1. Full-tendon augmented transp 4XP with resection of RSR R to RMR, ciliary sparing, botox RLR 2. Harada-Ito R 2 LHT 1. Partial aug transp with resec 4 Rhypo RSR, R to RMR with ciliary vessel sparing, recess RLR 2. Rerecess RLR 9 50 RXT Absent RMR and R 1. Full tendon transp with resection of RSR, R to RMR, botox RLR 10 RHT 10P, RHT 40D Tethering of R to orbital floor with scar tissue XT, 12 RHT, pupil dilated Entrapment/transection RMR, R, and inf division third nerve 12 XT-100 Destruction LMR and L with no function, damage to L 8 RHT 2. L recess 8 XT 3. LLR Faden 1. Full-tendon augmented Ortho in prim. transposition of RMR, RLR to R 1. Ant orbitotomy with repair bony defect medial wall, freeing, restoration of orbital contents 1. Nasal periosteal globe fixation, extirpation of LLR, orbitotomy repair of floor fracture LXT-6 13 LHT 14 L intact, paretic 1. R recess 2 LHT RXT, 30 RHT Mild destruction of post-third Plan: Botox RLR, RSR MR, R intact LXT, 15 LHT LMR transection, L intact but not contracting Plan: LLR to orbital wall Ant anterior; aug augmented; Botox botulinum toxin; CSF cerebrospinal fluid; D downgaze; EP esophoria; ET esotropia; HT hypertropia; hypo hypotropia; Inf inferior; IO inferior oblique muscle; inferior rectus muscle; L left; LG left gaze; LR lateral rectus muscle; MR medial rectus muscle; ortho orthophoria; P primary position; partial TWT partial tendon-width transposition; R right; resec resection; superior oblique muscle; SR superior rectus muscle; transp transposition; U upgaze; XP exophoria; XT exotropia. *The procedures in the table are numbered to represent their sequence. 18 XT LHT-4

5 492 Volume 8 Number 5 October 2004 FIG 2. Axial MRI view of Case 11 suggestive of either entrapment of the MR in the sinus or its transection. Sagittal views showed the MR to be intact throughout its length but pulled into the sinus near the middle of the muscle, confirming its entrapment. FIG 1. Axial MRI views of Case 4 showing left medial rectus transection in the anterior third with the remaining posterior muscle segment intact and functional. MR and had a rapid recovery with full function over a three-month period. Case 2 had a slower recovery. Botulinum toxin injection of the antagonist LR was performed in the clinic. Incomplete recovery of MR function resulted in limitation to adduction in the involved right eye and exotropia in left gaze. The patient was satisfied with correction of his head turn and single vision in the primary position and refused the suggested faden procedure on the left LR. In Case 14, there was damage to the posterior third of the MR and contusion to the with possible injury to the inferior division of the third nerve with associated paresis of both MR and. We plan to inject botulinum toxin into the LR and superior rectus and observe muscle recovery. In Cases 3, 4, and 5 the MR was recovered through an anterior orbitotomy approach and was reattached to the globe. This was combined with botulinum toxin injection in the antagonist LR. These were the cases of muscle transection where the remaining posterior MR segment was long; the muscle showed some contractility on multipositional MRI scanning (Figure 1) or the muscle was only partially damaged. In Case 11, on axial MRI scans it was difficult to distinguish muscle transection from entrapment in the FIG 3. Preoperative clinical photos of Case 11 showing right exotropia of 35 prism diopters and right hyperopia of 12 prism diopters with limitation of adduction and elevation. Note dilated fixed right pupil. medial orbital wall bony defect (Figure 2). The mid portion of the muscle segment seemed transected. Sagittal views showed the MR to be intact throughout its length, ruling out transection. This emphasizes the need for assessment of different image planes. Clinically there was evidence of MR and damage. An ipsilateral fixed pupil suggested that the inferior division of the third nerve was involved (Figure 3). Anterior orbitotomy was performed to explore the medial orbit. The MR and muscles were found intact in the ethmoid sinus and repositioned in the orbit. Postoperatively the pupil returned to normal size, shape, and reactivity and the muscle function has continued to improve (Figure 4). In Cases 6, 7, and 8, the MR was transected but the remaining proximal stumps were very short and no attempts were made to recover the stumps. In Case 9, the MR and in Case 10 the were irreparably damaged (no

6 Volume 8 Number 5 October FIG 4. Postoperative clinical photo of Case 11 after orbitotomy and repositioning the intact MR and into the orbit. Note that the right pupil has normalized. significant muscle tissue remained). Appropriate transposition procedures were hence performed in these cases. Case 5 needed transposition as a second procedure following reattachment of a short 7-mm MR posterior stump. Even though the MR stump was reattached, it was nonfunctional. In Cases 12, 4, and 15, the vertical rectus muscle transpositions to the MR insertion would have been valuable but were infeasible due to coexistent damage. In Case 12, there was severe destruction and no function of both the ipsilateral MR and muscles. Hence a nasal orbital periosteal flap was created and anchored to the globe at the MR insertion site. 15 This was combined with extirpation of the ipsilateral LR muscle. The globe was fixed in the primary position. In Case 4, the original injury from the endoscopic surgery was to the MR alone, but a nasal rupture of the ipsilateral complicated a Hummelscheim procedure at another institution (Figure 5). Preoperative iris angiography performed five months after the initial injury revealed delayed filling along the medial and inferior iris quadrants and transposition surgery was not performed. Preoperative multipositional MRI scan of the orbit revealed a functional posterior 20-mm MR stump. A repeat orbitotomy recovered the MR. Marked improvement in horizontal alignment was achieved after the MR posterior stump was reattached to the sclera (Figure 6). Case 15 had imaging evidence of MR transection with no recoverable posterior segment, and ipsilateral paresis with no significant recovery of function. A transposition procedure is thus not an option. We plan to disinsert the LR and reattach it to the lateral orbital wall. Case 13 had mild damage only to the, whose function did not return completely after 8 months. Contralateral recession was performed to correct the ipsilateral hypertropia. FIG 5. Preoperative clinical photos of Case 4. Note left exotropia of 14 prism diopters and left hypotropia of 12 prism diopters with limitation of adduction. Also note the limitation to elevation, which was due to repair of incidental rupture on earlier attempted transposition surgery prior to being seen at our institution. The previous surgeon secured the rupture together which presumably caused a shortening or restriction effect on the. FIG 6. Postoperative clinical photos of Case 4 after orbitotomy, recovery, and reattachment of the proximal functional 20-mm MR stump. No horizontal heterotropia was noted postoperatively in the primary position. There was a residual left hypotropia of 6 prism diopters in the primary position. Two cases had associated optic nerve damage impairing vision to 20/100 in Case 8 and complete blindness of an eye in Case 15. Postoperatively 10 of the 11 (91%) operated cases had a small residual deviation in the primary position and were functioning binocularly in daily life. Case 11 had a residual 7-degree left face turn and a 20-prism diopter exotropia. DISCUSSION Varying degrees of damage can occur to several extraocular muscles as a complication of endoscopic sinus surgery. The resultant strabismus may leave the patient severely incapacitated due to abnormal head position and/or diplopia. Management of these complications is challenging. Retrieval of a transected muscle is difficult as the posterior muscle portion may retract posteriorly, necessitating or-

7 494 Volume 8 Number 5 October 2004 bital surgical approaches. Muscle recovery is not always possible because of muscle destruction or severe damage with entrapment in scar tissue. In our series, the MR was the most commonly traumatized muscle. There are other reports of isolated MR muscle injury complicating endoscopic sinus surgery. 17,18,19 In addition, we found that the and muscles may also be damaged. To our knowledge, there have been no previous reports of either or muscle damage noted with endoscopic sinus surgery. Two of the patients in this series had associated optic nerve damage. There have been two previous reports of similar injuries. 16,19 High-resolution CT and surface coil MRI proved essential in determining the extent and nature of muscle injury. The added benefit of multipositional MRI was that it demonstrated muscle contractility. This provided a more precise diagnosis in complicated cases and helped to devise the most suitable treatment plan. We suggest that multipositional MRI scanning be part of the standard protocol for the work-up of such cases. Iris angiography was informative in complicated cases where multiple surgeries were required on multiple muscles. It guided us to alter surgical plans to avoid anterior segment ischemia. Timing and type of surgical intervention depend on severity, type of injury, and number of muscles involved. Based on the results of our experience with these cases, the following management strategy is suggested. In cases where the involved muscle is intact but paretic due to contusion injury or injury is to its nerve (as noted on imaging), no immediate surgical intervention is suggested. The antagonist rectus muscle may be injected with botulinum toxin while awaiting recovery of the paretic muscle to avoid its contracture. In more severely damaged muscles, early surgical intervention is appropriate and the surgical strategy depends on the nature of the muscle injury. We suggest that in cases with transection injury, if the remaining posterior segment of the MR is longer than 20 mm and is functional, muscle recovery via anterior orbital approach should be attempted. This requires the added expertise of an orbital surgeon. If the injury is more severe with excessive muscle destruction, muscle transposition procedures may be helpful and the potentially hazardous posterior orbital exploration may be avoided. In cases where there is coexistent injury, vertical rectus muscle transposition procedures may not be possible. Inactivating the antagonist muscle and creating a force upon the eye to center it with the use of an orbital periosteal flap can be performed in such cases. References 1. Schaefer SD, Manning S, Close HG. Endoscopic paranasal sinus surgery: Indications and consideration. Laryngoscope 1989;99: Etizen JP, Elsas FJ. Strabismus following endoscopic intranasal sinus surgery. J Pediatr Ophthalmol Strabismus 1991;28: Neuhans RW. Orbital complications secondary to endoscopic sinus surgery. Ophthalmology 1990;97: Krouse JH, Stankiewiez JA. Complications of powered endoscopic sinus surgery and their management. In: Krause JH, Christmas DA, editors. Powered Endoscopic Sinus Surgery, Chapter 12. Baltimore, MD: Williams and Wilkins; Underdahl JP, Demer JL, Goldberg RL, Rosenbaum AL. Orbital wall approach with preoperative orbital imaging for identification and retrieval of lost or transacted extraocular muscles. J Am Assoc Pediatr Ophthalmol Strabismus 2001;5: Shin GS, Demer JL, Rosenbaum AL. High resolution, dynamic, magnetic resonance imaging in complicated strabismus. J Pediatr Ophthalmol Strabismus 1996;33: Mehta A. Chief complaint, history and physical examination. In: Rosenbaum AL, Santiago AP, editors. Clinical Strabismus Management: Principles and Surgical Techniques, Chapter 1. Philadelphia: WB Saunders; pp Metz HS. Forced duction, active force generation and saccadic velocity tests. Int Opthalmol Clinics 1976;16: Rosenbaum AL. The clinical application of saccadic velocity testing. In: Souza-Diaz C, editor. Smith Kettlewell Symposium on Basic Sciences in Strabismus. Mechanical Factors on Strabismus Diagnosis and Surgery. Annex to the 5th Congress of the Latin American Council of Strabismus, Guaruya, CLADE; Demer JL, Miller JM. Orbital imaging in strabismus surgery. In: Rosenbaum AL, Santiago AP, editors. Clinical Strabismus Management: Principles and Surgical Techniques, Chapter 6. Philadelphia: WB Saunders; pp Santiago AP, Rosenbaum AL. Selected transposition procedures. In: Rosenbaum AL, Santiago AP, editors. Clinical Strabismus Management: Principles and Surgical Techniques, Chapter 36. Philadelphia: WB Saunders; pp Foster RS. Vertical muscle transpositions augmented with lateral fixation. J Am Assoc Pediatric Ophthalmol Strabismus 1997;1: Velez FG, Rosenbaum AL. Partial augmented transpositions. In: Smith Kettlewell Eye Research Institute, editor. Festschrift for Arthur Jampolsky. San Francisco, CA: The Smith Kettlewell Eye Research Institute, pp McNeer KW, Magoon EH, Scott AB. Chemodenervation therapy: Technique and indications. In: Rosenbaum AL, Santiago AP, editors. Clinical Strabismus Management: Principles and Surgical Techniques, Chapter 32. Philadelphia: WB Saunders; Goldberg RL, Rosenbaum AL, Tong JT. Use of apically based periosteal flap as globe tethers in severe paretic strabismus. Arch Ophthalmol 2000;118: Stankiewicz JA. Blindness and intranasal endoscopic ethmoidectomy. Prevention and management. Otolaryngol Head Neck Surg 1989; 101: Rene C, Rose GE, Lenthall R, Moseley J. Major orbital complications of endoscopic sinus surgery. Br J Ophthalmol 2001;85: Buus DR, Tse DT, Farris, BK. Ophthalmic complications of sinus surgery. Ophthalmology 1990;97: Corey JP, Bumsted R, Panje W, Namson A. Orbital complications in functional endoscopic sinus surgery. Sect Otolaryngol Head and Neck Surg 1993;5: