Surgical Treatment of Strabismus Secondary to Glaucoma Drainage Device

CLINICAL SCIENCES Surgical Treatment of Strabismus Secondary to Glaucoma Drainage Device

Alejandra Roizen, MD; Noa Ela-Dalman, MD; Federico G. Velez, MD; Anne L. Coleman, MD, PhD; Arthur L. Rosenbaum, MD

Objective: To describe surgical strategies in a series of mary position was eliminated in 5 patients and mark- patients with diplopia following implantation of a glau- edly improved in 3 patients. coma drainage device. Conclusions: Strabismus following implantation of a Methods: Retrospective review of 9 consecutive pa- glaucoma drainage device is an uncommon but serious tients who underwent strabismus surgery because of stra- complication. Restoration of ocular alignment is a com- bismus and diplopia after implantation of a glaucoma plex undertaking requiring strabismus and glaucoma sur- drainage device. gical expertise. Multiple surgical complications may oc- cur. Surgical intervention may require complete removal Results: Seven patients with marked limitation to ocu- of the fibrous capsule surrounding the implant and in- lar rotations and incomitant strabismus underwent sur- volved adjacent structures. Size reduction of the im- gery on the eye with the implant. Two patients with mild plant plate is helpful and did not interfere with postop- limitation to ocular rotations of the involved eye under- erative intraocular pressure control in this study. Surgery went surgery on the contralateral eye. All patients had a on the contralateral eye is an option in patients with mild large fibrous capsule surrounding the implant plate, ad- restriction. jacent muscles, and sclera. Intraocular pressure was not elevated postoperatively. Postoperative diplopia in the pri- Arch Ophthalmol. 2008;126(4):480-486

TRABISMUS FOLLOWING IM- incidence of ischemia, necrosis, direct plantation of a glaucoma trauma, and scarring between muscles drainage device has been re- and the implant.2,8 Implantation of a glau- ported by several authors.1-12 coma drainage device in the superonasal In many cases, the diplopia is quadrant has been reported to cause transient because it is caused by extraocu- pseudo-Brown syndrome.3,8-11 S 1 lar muscle and orbital tissue edema. How- Treatment of strabismus following im- ever, there are cases of permanent strabis- plantation of glaucoma drainage devices mus secondary to a mass effect, a posterior is challenging. Deviations are usually in- fixation suture effect, the incorporation of comitant. Some patients may be reluc- extraocular muscles in the capsule sur- tant to consent to surgery on the contra- rounding the implant, fat adherence to the lateral eye. In addition, strabismus surgery implant, and/or direct trauma to the ex- on the eye containing the glaucoma drain- traocular muscles.1-7 age device may jeopardize the implant’s The incidence of permanent strabis- function.1,5 mus after implantation of glaucoma drain- To our knowledge, there have been no age devices ranges from 6% to 100% and reports describing the different surgical ap- appears to depend on the type of implant proaches for correcting strabismus after the Author Affiliations: Pediatric used, where the implant is placed, and the implantation of glaucoma drainage de- Ophthalmology and Strabismus 1 and Glaucoma Divisions, implant material. The bigger the im- vices. The purpose of this study was to de- Department of Ophthalmology, plant, the higher the risk of developing scribe the different surgical strategies used Jules Stein Eye Institute, motility disturbances. Implants that re- in a series of patients with diplopia fol- University of California, quire positioning of the device’s edges un- lowing implantation of a glaucoma drain- Los Angeles. der the extraocular muscles have a higher age device.

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Figure 1. Patient 9. A, After Ahmed valve implantation, exotropia and hypertropia are evident in the left eye. B, The limitation to adduction and downward rotation in the left eye markedly improved postoperatively.

METHODS ment of the nonfixing eye. In cases where the visual acuity in either eye was 1.3 or more logarithm of the minimum angle of resolution lines, the Krimsky test was performed to assess ocu- We conducted a retrospective review of 9 patients with stra- lar alignment.13 Sensory response was evaluated with the Tit- bismus and diplopia after implantation of a glaucoma drain- mus stereo test (Stereo Optical Co, Inc, Chicago, Illinois). age device. All patients had extraocular muscle surgery per- Subjective torsion was measured with the double Maddox formed by the same surgeon (A.L.R.) between January 1, 1997, rod test. Two Maddox rod cylinders, one red and one green, and December 31, 2005. Appropriate internal review board ap- were placed in a trial frame. The patient was asked to rotate proval was obtained. each knob on the frame until the red and green lines were both All patients underwent an ocular examination that in- cluded the measurement of distance acuity, near visual acuity, parallel to the floor. The amount of cyclotorsional deviation and cycloplegic refraction (with the use of cyclopentolate hy- (in degrees) was determined directly from the axis scale on the drochloride 1%); a slitlamp examination; and a dilated fundus trial frame after the patient made the proper adjustment. Ob- examination. The visual acuity was measured for distance with jective torsion was determined by the position of the macula best correction using a binocular testing system (Mentor Bin- relative to the optic nerve during examination of the posterior ocular Visual Acuity Testing; Medtronics Solan, Jacksonville, pole with the use of an indirect ophthalmoscope and a 20- 14 Florida) with Snellen optotypes at 20 feet. Intraocular pres- diopter lens, as described elsewhere. sure was measured with the Goldman applanation tonometer A forced-duction test was performed at the beginning of the preoperatively and postoperatively on the first day after sur- surgical procedure and then intraoperatively to determine the gery, 2 months later, and then periodically as recommended area of mechanical restriction and to confirm release of the re- by the glaucoma specialist. All patients’ ductions and versions striction, respectively. This was performed by carefully grab- were assessed preoperatively and postoperatively in the 9 gaze bing the limbus with a toothed forceps on the opposite side of positions (Figure 1).11 the gaze limitation, causing slight protrusion of the eye, and Motor alignment was determined by prism cover testing while then rotating the eye in the direction of the limited duction.15 the subject was fixing at a 20/70 target at 6 meters and at 35.6 In all cases, the origin of restriction was determined to be in cm. A prism bar was held in front of the affected eye while an the area of the valve. optical occluder covered the prism over the nonfixing eye. The The ultimate goal was to free all restrictions. To achieve this, patient was asked to fix with the unaffected eye. The optical we removed (as much as technically possible) the fibrous cap- occluder was then moved away from the affected eye to cover sule surrounding the valve and its extensions (Figure 2 and the unaffected eye. The angle of deviation was determined by Figure 3). A limbal incision was performed to isolate the su- measuring the amount of prism required to neutralize the move- perior rectus and lateral rectus muscles. In dissecting these

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C D

Figure 2. Patient 2. A, The scissors point to the thick fibrotic capsule (FC) covering the implant; the FC extends from the superior rectus muscle (SR) (arrow) to the lateral rectus muscle. B, The implant with part of the FC (arrow) dissected. C, The valve plate is almost fully exposed. D, Note the implant’s size relative to the eye. The scissors are cutting a fibrous band that goes through the valve’s pore.

muscles, we encountered the fibrous capsule adjacent to or ex- horizontal, and torsional diplopia. The mean interval be- tending along the bellies of the superior rectus or lateral rec- tween implantation of the glaucoma drainage device and tus muscles. It then was necessary to excise the fibrous cap- the onset of diplopia was 23.5 days (range, 1-90 days). sule to reveal the muscle and free the restriction. No patient had diplopia before the glaucoma drainage device was implanted. RESULTS Six of 9 patients (67%) had exotropia and vertical deviation in the primary position. Four of those 6 patients The preoperative and operative patient characteristics are (67%) had hypotropia of the affected eye and 2 of the 6 summarized in Table 1. The mean age at the time of patients (33%) had hypertropia of the affected eye. Two strabismus surgery was 71.2 years (age range, 49-86 years). of the 9 patients (22%) had esotropia and vertical devia- Eight of the 9 patients reported diplopia. Six of those 8 tion in the primary position. patients (75%) had vertical and horizontal diplopia, 1 The mean preoperative intraocular pressure was 12.7 (12%) had vertical diplopia, and 1 (12%) had vertical, mm Hg preoperatively (range, 6-16 mm Hg). Eight pa-

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LR LR

Figure 3. Patient 2. A, The hook is under the lateral rectus muscle (LR). The fibrotic capsule (FC) covering the implant extends to the LR. B, The LR is disinserted and reflected from the sclera. The scissors are cutting the FC extensions between the sclera and the LR. C, The FC extensions (top arrow) continue to be removed from the LR (bottom arrow) and sclera far posteriorly.

Table 1. Preoperative and Operative Patient Characteristics

Patient No./ Diplopic Alignment Torsion, IOP, Stereopsis, EOM Glaucoma Age, y Implant/Location Field in PP, PD Degrees mm Hg Seconds of Arca Operation Implant Surgery 1/74 Baerveldt/OS SN LG RHT, 1; 5 Ex 10 400 RLR: rec 12 mm, None RG XT, 4; res 7.5 mm; LG ET, 10 RMR: Faden procedure 2/70 Baerveldt/OS ST All gazes XT, 20; 13 Ex 16 Fly LSR: rec 6 mm; Capsule excision, LHoT, 14 LLR: rec 6 mm; Baerveldt removal, LSO: reatt Ahmed valve implantation IN 3/58 Ahmed/OD SN None XT, 25; RHoT, 15 5 Ex 16 Fly RIR: rec 4 mm; Capsule excision (poor VA) RLR: rec 9 mm 4/86 Ahmed/OD ST All gazes XT, 20; RHT, 18 3 Ex 16 NA RLR: rec 6 mm; Capsule excision, RSR: rec 6 mm adhesion released between RSO and valve 5/49 Ahmed/OS ST All gazes ET, 15; NA 12 Fly LMR: rec 3 mm Scar tissue removal LHoT, 3 6/65 Ahmed/OD SN All gazes XT, 15; NA 12 Fly RSO: rep; Capsule excision, and STb RHoT, 20 RLR: rec 7 mm adhesion release; RSR, valve insertion SN; valve trimming 7/81 Ahmed/OD ST PP, LG ET, 8; 5 Ex 12 Fly RIR: rec 4 mm Scar tissue excision RHoT, 14 8/80 Ahmed/OS ST All gazes XT, 10; 5 Ex 6 Fly RLR: rec 7.5 mm; None LHoT, 8 RSR: rec 4.5 mm 9/78 Ahmed/OS ST All gazes XT, 35; 5 In 14 Fly LSR: rec 7 mm; Capsule excision; LHT, 20 LLR: rec 7 mm; revision valve LSO: rep

Abbreviations: EOM, extraocular muscle; ET, esotropia; Ex, excyclotorsion; In, incyclotorsion; IN, inferonasal; IOP, intraocular pressure; LG, left gaze; LHoT, left hypotropia; LHT, left hypertropia; LLR, left lateral rectus muscle; LMR, left medial rectus muscle; LSO, left superior oblique tendon; LSR, left superior rectus muscle; NA, not available; OD, right eye; OS, left eye; PD, prism diopters; PP, primary position; reatt, reattachment; rec, recession; rep, repositioning; res, resection; RG, right gaze; RHoT, right hypotropia; RHT, right hypertropia; RIR, right inferior rectus muscle; RLR, right lateral rectus muscle; RMR, right medial rectus muscle; RSO, right superior oblique tendon; RSR, right superior rectus muscle; SN, superonasal; ST, superotemporal; VA, visual acuity; XT, exotropia. a Fly indicates 3000 seconds of arc. b This patient had 2 implants in 1 eye.

tients had 1 implant in 1 eye and 1 patient had 2 im- One patient with a superotemporal implant had restric- plants in 1 eye. Seven devices were implanted in the su- tion to downgaze and adduction. perotemporal quadrant and 3 were implanted in the The surgical approach was individually tailored to each superonasal quadrant. patient. All of the surgical procedures, except for 1 re- Intraoperative forced-duction test results showed reoperation, were performed with the patient under gen- striction to ocular rotations in all 9 patients. Four pa- eral anesthesia. All patients underwent limbal conjunc- tients had restriction to ocular rotations in all fields. Two tival incision near the drainage device. The incision was of the 3 patients with superonasally implanted devices extended with 2 radial incisions to the area of the adja- had restriction to adduction and elevation in adduction. cent rectus extraocular muscle for better exposure of the

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Patient F/U, IOP, Alignment Torsion, Stereopsis, Patient Strabismus No. mo mm Hg in PP, PD Degrees Seconds of Arca Diplopic Field Satisfaction Reoperation 1 3 18 Ortho, LG None Fly− Extreme RG Yes No 2 12 10 Ortho 3 Ex 50 No Yes RMR rec 6 mm, res 3 mm 3 4 15 XT, 4; RHoT, 10 None Fly No Yes No 4 12 NA XT, 2; RHT, 2 None NA Vertical Yes No; required 2 PD 5 1 14 Ortho None Fly No Yes No 6 4 12 XT, 5 None 3000 No Yes No 7 12 9 HT, 3 None 3000 No Yes RIR adv 2 mm 8 48 12 ET, 2; LHoT, 4 3 Ex Fly Intermittent in PP No No 9 4 14 XT, 6 None Fly Reading position Yes No; separate reading Rx

Abbreviations: adv, advancement; ET, esotropia; Ex, excyclotorsion; F/U, follow-up; HT, hypertropia; IOP, intraocular pressure; LG, left gaze; LHoT, left hypotropia; NA, not available; ortho, orthotropia; PD, prism diopters; PP, primary position; rec, recession; RG, right gaze; RHoT, right hypotropia; RHT, right hypertropia; RIR, right inferior rectus muscle; RMR, right medial rectus muscle; Rx, prescription; XT, exotropia. a Fly indicates 3000 seconds of arc.

muscle, drainage device, and scar tissue. All patients un- mm Hg). After surgery, no patient had uncontrolled in- derwent strabismus surgery with an adjustable suture tech- traocular pressure on any examination. Two patients with nique; sutures were adjusted on the first postoperative preoperative diplopia and 1 patient without preopera- day. At the end of the procedure, 0.5 mL of dexameth- tive diplopia owing to poor vision were diplopia free in asone was injected subconjunctivally in the area adja- all fields of gaze after the initial strabismus surgery. Two cent to the extraocular muscle undergoing operation. patients were diplopia free in the primary position after Seven patients underwent surgery on the eye with the they underwent a second strabismus surgery because of implant. All of them had marked limitation to ocular ro- an inferior rectus muscle slippage. Diplopia in the pri- tations and incomitant strabismus. Two patients with mild mary position improved but persisted in 3 patients: 2 pa- limitation to ocular rotations of the involved eye under- tients had a smaller deviation and were diplopia free with went strabismus surgery on the contralateral eye. prisms and 1 had intermittent diplopia. All patients had a large fibrous capsule surrounding the implant plate, adjacent muscles, and sclera. Once the capsule was trimmed and opened, aqueous fluid was dis- COMMENT charged. To prevent a flat chamber and complications such as cataract, severe hypotony, or decentered intraocular The incidence of strabismus following implantation of lenses, a clear corneal paracentesis was performed by the glaucoma drainage devices is variable; it appears to be glaucoma specialist (A.L.C.) and the anterior chamber more common following placement of large-plate im- was reformed by injecting either sodium hyaluronate plants. Previous authors1,14,16,17 have reported more than (Healon; Advanced Medical Optics Uppsala AB, Uppsala, an 80% incidence of strabismus following implantation Sweden) or balanced saline solution through the para- of the 350-mm2 Baerveldt implant or the Krupin valve centesis. In all of the patients, scar tissue incorporated with disc. In our study, 7 patients had had an Ahmed valve the adjacent extraocular muscles. implanted. To our knowledge, the incidence of strabis- In 2 patients, the implant was trimmed and reposi- mus following Ahmed valve implantation is not re- tioned, which eliminated the mass effect of the implant. ported in the literature, and there are only a few reports Three patients with superonasal implants had scar tis- of strabismus after implantation of the device.6,18 The sue between the superior oblique tendon and the supe- Ahmed valve may induce fewer motility disturbances be- rior rectus muscle. In these 3 patients, the scar tissue was cause its surface area (184 mm2) is smaller than that of removed and the superior oblique tendon was reposi- the double-plate Molteno (270 mm2) or the Baerveldt (350 tioned. In 1 patient the anterior portion of the superior mm2) implant.1,19 oblique tendon was disinserted from the sclera and was We found that limitation to ocular rotations in fields attached to the surrounding scar tissue. Another patient of gaze away from the implant and deviation toward the with a functional Baerveldt implant had a dense capsule implant is most likely due to the presence of the fibrous between the superior and lateral rectus muscles that ex- capsule surrounding the implant, which causes marked tended 21 mm posteriorly to the limbus. It was neces- restriction to ocular rotations. Superonasal implanta- sary to remove the Baerveldt implant to expose all the tion may create hypotropia with limitation to elevation scar tissue attachments and to release the restriction. The in adduction.2,6,9 Two of our patients had limitation to Baerveldt implant was replaced with an Ahmed glau- elevation in adduction; both patients had implants in the coma drainage device, which was implanted inferona- superonasal quadrant. sally to avoid the superotemporal quadrant. One patient had 13° of excyclotorsion. Surgical ex- Postoperative follow-up ranged from 1 to 48 months ploration showed partial disinsertion of the anterior half (Table 2). At the last postoperative follow-up visit, the of the superior oblique tendon, which was sitting di- mean intraocular pressure was 13.0 mm Hg (range, 9-18 rectly under the implanted valve. As soon as the valve

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SOT SR

Figure 4. Patient 2. A, The forceps are holding the insertional edge of the superior oblique tendon (SOT) (arrow), which was inadvertently disinserted when the glaucoma drainage device was implanted. The scissors are pointing to the anterior edge of the SOT’s insertional stump. B, Reinsertion of the SOT with nonabsorbable sutures. C, The superior rectus muscle (SR) (arrow) was recessed with an adjustable suture. An Ahmed valve was implanted inferonasally (not shown) as a replacement for the removed implant.

was elevated, prior to any tissue dissection, it was ap- terior chamber with sodium hyaluronate or balanced sa- parent that the tendon was not in its normal location. The line solution and maintain intraocular pressure. Once the anterior portion of the superior oblique tendon most likely anterior chamber is reformed and the pressure is nor- was accidentally detached from its insertion during im- malized, strabismus surgery can continue, restrictions can plantation of the valve. The superior oblique tendon was be relieved, and the appropriate muscles can be re- reinserted in its normal position with a nonabsorbable cessed. Then, the glaucoma specialist can address the is- suture, resulting in the absence of excyclotorsion post- sues of valve reduction and removal of viscoelastic ma- operatively (Figure 4). terial. Extensive scar tissue dissection may result in We found it necessary to eliminate the restriction damage to the conjunctiva. Careful conjunctival dissec- caused by the fibrous capsule that surrounds the im- tion is warranted to prevent complications during con- plant in 5 of our 9 patients. We also found it necessary junctival closure and to decrease the potential risk of en- to explore the extraocular muscles adjacent to the im- dophthalmitis in a patient who has a glaucoma drainage plant in all cases to ensure that they were intact and to device. excise the fibrous capsule. This was contrary to previ- Strabismus surgery secondary to a glaucoma drain- ous reports that recommended only recession of the ad- age device is a complex procedure with potential com- jacent or opposing muscles to avoid creating a persis- plications such as cataract, decentered intraocular lens, tent restriction.1 hypotony, difficulties with conjunctival closure, post- The fibrous capsule was almost impossible to dissect operative infection, endophthalmitis, and intraocular pres- in its entirety. The scar tissue, which was extensive in sure spikes owing to retained viscoelastic material. The all cases, was removed until the restriction on forced- postoperative intraocular pressures in our patients are duction testing was released or until it was no longer tech- shown in Table 2. Postoperative intraocular pressure fol- nically possible to continue. The fibrous capsule will prob- low-up ranged from 1 to 48 months. No patient re- ably recur once the implant begins to function because quired additional medication or glaucoma surgery. How- of the continuous aqueous flow. However, the smaller ever, this study was limited by the small number of size of the drainage device (accomplished by trimming patients and short follow-up. Longer postoperative fol- the valve or replacing it with a smaller device), exten- low-up with a glaucoma specialist is required to moni- sive dissection, intraoperative corticosteroid injection un- tor changes in intraocular pressure and in the optic nerve. der the Tenon capsule, and the fact that the implant was Treatment of strabismus following the implantation situated as far as possible from the adjacent extraocular of a glaucoma drainage device is challenging. Nonsur- muscles may prevent recurrence of the restriction. gical treatment is limited. Prisms usually do not help be- The main concern when operating on the eye that has cause the deviations are incomitant and sometimes large. the drainage implant is the risk of damaging the im- To our knowledge, there are no reports of the use of che- plant’s ability to control intraocular pressure.1,2,19 These modenervation in these patients.1 In cases of mild re- patients usually have advanced glaucoma and intraocu- striction of the ocular rotations and a comitant strabis- lar pressure that is difficult to control. It is advanta- mus deviation, surgery on the contralateral eye has the geous to have a glaucoma surgeon available to help with advantage of being technically easier, more predictable, managing changes in aqueous flow when the fibrous cap- and associated with less risk of damaging the glaucoma sule is opened, trimming or replacing the glaucoma drain- drainage implant. age implant, and reforming the anterior chamber. When From this study, we cannot conclude which charac- the integrity of the fibrous capsule is violated, aqueous teristics of the deviation predict the need for capsule ex- humor is immediately discharged and the anterior cham- cision. Almost every case required some degree of scar ber flattens. This is the primary reason for including a tissue removal, especially when the forced-duction test glaucoma specialist, who can immediately reform the an- result was positive. Because the fibrous capsule is very

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©2008 American Medical Association. All rights reserved. Downloaded From: https://jamanetwork.com/ on 09/27/2021 extensive, the location of the drainage device should be 5. Mun˜oz M, Parrish R II. Strabismus following implantation of Baerveldt drainage explored directly if the restriction needs to be released. devices. Arch Ophthalmol. 1993;111(8):1096-1099. 6. Dobler-Dixon AA, Cantor LB, Sondhi N, Ku WS, Hoop J. Prospective evaluation In summary, strabismus after implantation of a glau- of extraocular motility following double-plate Molteno implantation. Arch coma drainage device is an uncommon but serious com- Ophthalmol. 1999;117(9):1155-1160. plication. Removal of the fibrous capsule surrounding the 7. Wilson-Holt N, Franks W, Nourredin B, Hitchings R. Hypertropia following in- implant is essential to release restrictions identified on sertion of inferiorly sited double-plate Molteno tubes. Eye. 1992;6(pt 5):515- forced-duction testing. However, appropriate rectus ex- 520. traocular muscle recession with the use of adjustable su- 8. Prata JA Jr, Minckler DS, Green RL. Pseudo-Brown’s syndrome as a complication of glaucoma drainage implant surgery. Ophthalmic Surg. 1993;24(9):608- tures is required to achieve ocular alignment. 611. 9. Ball SF, Ellis GS Jr, Herrington RG, Liang K. Brown’s superior oblique tendon Submitted for Publication: April 19, 2007; final revi- syndrome after Baerveldt glaucoma implant. Arch Ophthalmol. 1992;110(10): sion received July 26, 2007; accepted August 5, 2007. 1368. Correspondence: Arthur L. Rosenbaum, MD, Depart- 10. Coats DK, Paysee EA, Orenga-Nania S. Acquired Pseudo-Brown’s syndrome immediately following Ahmed valve glaucoma implant. Ophthalmic Surg Lasers. ment of Ophthalmology, Jules Stein Eye Institute, 100 1999;30(5):396-397. Stein Plaza, University of California, Los Angeles, Los An- 11. Dobler AA, Sondhi N, Cantor LB, Ku S. Acquired Brown’s syndrome after a double- geles, CA 90095 ([email protected]). plate Molteno implant. Am J Ophthalmol. 1993;116(5):641-642. Financial Disclosure: None reported. 12. Rhee DJ, Casuso LA, Rosa RH Jr, Budenz DL. Motility disturbance due to true Funding/Support: Dr Rosenbaum is a recipient of a Re- tenon cyst in a child with a Baerveldt glaucoma drainage implant. Arch Ophthalmol. search to Prevent Blindness Physician Scientist Merit 2001;119(3):440-442. 13. Metha A. Chief complaint, history and physical examination. In: Rosenbaum A, Award. Santiago P, eds. Clinical Strabismus Management. Philadelphia, PA: WB Saun- Previous Presentation: This study was presented at the ders Co; 1999:3-21. Annual Meeting of the American Association for Pedi- 14. Phillips PH, Hunter DG. Evaluation of ocular torsion and principles of management. atric Ophthalmology and Strabismus; April 14, 2007; Se- In: Rosenbaum A, Santiago P, eds. Clinical Strabismus Management. Philadel- attle, Washington. phia, PA: WB Saunders Co; 1999:52-72. 15. Rosenbaum A, Santiago P. Test of muscle function. In: Rosenbaum A, Santiago P, eds. Clinical Strabismus Management. Philadelphia, PA: WB Saunders Co; 1999: REFERENCES 37-51. 16. Cardakli UF, Perkins TW. Recalcitrant diplopia after implantation of a Krupin valve 1. Rosenbaum A, Santiago P. Strabismus after glaucoma implant procedures. In: with disc. Ophthalmic Surg. 1994;25(4):256-258. Rosenbaum A, Santiago P, eds. Clinical Strabismus Management. Philadelphia, 17. Frank JW, Perkins TW, Kushner BJ. Ocular motility defects in patients with the PA: WB Saunders Co; 1999:304-307. Krupin valve implant. Ophthalmic Surg. 1995;26(3):228-232. 2. Smith SL, Starita RJ, Fellman RL, Lynn JR. Early clinical experience with the 18. Ventura MP, Viana RN, Souza Filho JP, Solari HP, Curi RL. Acquired Brown’s Baerveldt 350-mm2 glaucoma implant and associated extraocular muscle syndrome secondary to Ahmed valve implant for neovascular glaucoma. Eye. imbalance. Ophthalmology. 1993;100(6):914-918. 2005;19(2):230-232. 3. Christmann LM, Wilson ME. Motility disturbances after Molteno implants. J Pe- 19. Damji K, Freedman S, Moroi S, Shafranov G. Drainage implant surgery. In: Alling- diatr Ophthalmol Strabismus. 1992;29(1):44-48. ham R, Damji K, Freedman S, Moroi S, Shafranov G, Shields B, eds. Shield’s 4. Mun˜oz M, Parrish R. Hypertropia after implantation of a Molteno drainage device. Textbook of Glaucoma. 5th ed. Philadelphia, PA: Lippincott Williams & Wilkins; Am J Ophthalmol. 1992;113(1):98-99. 2005:610-621.

Correction

Error in “Report of a Case” Section. In the Case Report titled “Dorsal Midbrain Syndrome With Bilateral Supe- rior Oblique Palsy Following Brainstem Hemorrhage,” published in the December 2006 issue of the Archives (2006;124(12):1786-1788), on page 1786, third col- umn, line 9, the incorrect published statement reads “Right head tilt revealed 20 ⌬ esotropia with 12 ⌬ left hypertropia, and left head tilt showed 25 ⌬ esotropia with 4 ⌬ left hypertropia.” The statement should have said that on left head tilt the patient showed 25 ⌬ esotropia with 4 ⌬ right hypertropia.

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