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Authors' Response: Active Pulleys in the Anophthalmic Socket
Role of Rectus Extraocular Muscle Pulleys
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Joseph Demer, Professor of Ophthalmology & Nuerology Jules Stein Eye Institute, UCLA
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jld{at}ucla.edu Joseph Demer
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Dr. Gigantelli raises some interesting issues regarding the possible role of the insertions of the orbital layers of the rectus extraocular muscles (EOMs) on their connective tissue pulleys in the anophthalmic socket. Our paper dealt with normal orbital anatomy and physiology.1 However, we have made a point to photograph the orbital layer insertions on each of the pulleys during enucleation surgery. If the EOM tenotomies are performed without excessive disssection of the pulley tissues, the EOMs will following enucleation of the globe retract only to the points of insertion of the orbital layers on the pulleys. This is true for the inferior oblique as well as for the rectus EOMs. On mechanical grounds, it seems likely that contraction of the orbital layers would continue to posteriorly displace the pulleys even in the anophthalmic socket. Confirmation of this supposition by magnetic resonance imaging (MRI) is a challenging proposition due to postsurgical distortions of orbital anatomy. As suggested by Dr. Gigantelli as one surgical option, it is our practive following enucleation to implant a silicone sphere in the orbit posterior to the dense circumferential portion of posterior Tenon’s fascia.2 We then suture the four ends of the rectus tendons together over the central opening in posterior Tenon’s fascia in no particular relationship to the spiral of Tilleaux, and over this close anterior Tenon’s fascia and the conjunctiva in layers. Although we do not place a peg in the sphere or make any other attempt to mechanically couple the prosthesis to it, post-operative motility of the prosthesis seems quite satisfactory. Similar satisfactory motility is also has been achieved even without implantation of any orbital sphere at all, provided that the orbital layers of the rectus EOMs are not detached from the pulley tissues. It is clear that the mechanically coupled network of the pulleys and posterior Tenon’s fascia is coupled to the eyelids and conjunctival fornices, and that this network is under the dynamic influence of the orbital layers of the rectus EOMs even after enucleation. Movement of the orbital connective tissues might even be chiefly responsible for prosthesis motility following enucleation. Conversely, the extensive dissection of pulley tissues required by alternative surgical approaches that isolate and suture individual EOMs to the sphere might conceivably impair the motility of the orbital connective tissues due to disinsertion of the orbital layers of the EOMs. Dr. Gigantelli raises a number of provocative questions regarding the mechanics of prosthesis motility, and the influence of technical aspects of surgical enucleation and sphere implantation. Having conducted only preliminary MRI imaging in anophthalmic orbits, we lack data to answer these questions. Such data might be provided by careful orbital imaging closely correlated with precisely-defined variation in surgical techniques. John L. Demer
References 1. Demer JL, Oh SY, Poukens V. Evidence for active control of rectus
extraocular muscle pulleys. Invest Ophthalmol Vis Sci. 2000;41:1280-
1290.
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James Gigantelli, Ophthalmic Plastic and Orbital Surgeon Department of Ophthalmology, University of Nebraska Medical Center
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jgigantelli{at}unmc.edu James Gigantelli
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I congratulate Dr. Demer and associates on their recent manuscript describing the existence of both orbital and global layers within the extraocular muscles.1 Through this manuscript and earlier publications, these investigators continue to advance our understanding of the complex role of orbital soft tissue relationships in ocular motility.2-8 While the authors' publications have thus far described normal relationships and relationships in orbits containing globes with dysmotility, the basic orbital anatomy and motility physiology also assists those of us who clinically manage anophthalmic sockets. Have the authors had an opportunity to translate their new findings to the anophthalmic socket, particularly following enucleation of the globe? At the time of enucleation, most individuals undergo placement of an alloplastic sphere implant within the extraocular muscle cone. They are then fit with an ocular prosthesis that is worn within the space created between the palpebral and former bulbar conjunctiva. For a few select individuals, motility of the prosthesis is elicited through rotational movement of the spherical intraconal implant. This is aided through coupling of the prosthesis to a biointegrated porous polyethylene or hydoxyapatite implant by means of a complex pegging system.9 The majority of anophthalmic patients do not undergo this coupling procedure. For these individuals, motility occurs through a different mechanism. Conventional belief has been that the ocular prosthesis displays passive motility resulting from conjunctival fornix deepening upon horizontal and vertical gaze.10 Have the authors investigated these extraocular muscle relationships in the anophthalmic socket? During surgical enucleation, the insertions of the extraocular muscle (global layer) are severed from the scleral surface of the globe. How does this process individually disturb the individual global and orbital layers of the extraocular muscles and their respective pulleys? To what level do either or both muscle layers contribute to conjunctival fornix deepening and postenucleation prosthetic motility? Some surgeons advocate "reinserting" the extraocular muscles onto the implant surface. Are these surgical efforts to reconstruct the Tillaux's spiral worthy relative to the physiology of postenucleation motility? Does the size of the orbital sphere implant alter extraocular muscle course and function, or prosthesis motility? I once again congratulate the authors and look forward to any insight they might provide to those of us who confront dysmotility not of the spherical globe but of noncoupled, aspherical anophthalmic prostheses. James W. Gigantelli References 1. Demer JL, Oh SY, Poukens V. Evidence for active control of rectus
extraocular muscle pulleys. Invest Ophthalmol Vis Sci. 2000;41:1280-1290.
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