Strabismus Surgery and Its Complications
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Strabismus Surgery and its Complications von David K Coats, Scott E Olitsky 1. Auflage Springer-Verlag Berlin Heidelberg 2007 Verlag C.H. Beck im Internet: www.beck.de ISBN 978 3 540 32703 5 Zu Inhaltsverzeichnis schnell und portofrei erhältlich bei beck-shop.de DIE FACHBUCHHANDLUNG Part I Surgical Management of Strabismus Chapter Surgically Important Anatomy 1 1 A clear grasp of the relevant anatomy and an understanding leys, and by transmitting forces generated by contraction of the of important anatomical variations are obvious prerequisites extraocular muscles indirectly to the sclera. Even a “lost” rec- for the strabismus surgeon. The strabismus surgeon must not tus muscle may continue to have a minor to moderate ability only be familiar with the anatomy of the extraocular muscles, to move the eye through these secondary attachments with the but must also be cognizant of adjacent structures in the orbit globe, despite complete disruption of the normal anatomical and the ocular adnexa. Much of the anatomy that the strabis- insertion. mus surgeon must be familiar with is covered routinely during This chapter will highlight key elements of ocular and or- the normal course of training in an ophthalmology residency bital anatomy that are important for the strabismus surgeon program. This standard training should be considered as an in- to understand. Major structures of anatomical importance in- troduction. The strabismus surgeon needs to understand many volving the eyelids, conjunctiva, Tenon’s fascia, and other or- intricacies of the ocular anatomy as they relate to cause and bital tissues will be reviewed, concluding with an assessment surgical treatment in order to both effectively plan and execute and review of key elements of the ocular and orbital anatomy surgery to correct strabismus. that the strabismus surgeon may encounter during surgery on A clear understanding of the implications of the palpebral individual extraocular muscles. Cross-referencing to chapters fissures and orbital shape, for example, is important not only on the recognition, prevention, and treatment of strabismus because it may affect surgical access to the extraocular muscles, surgery complications is made throughout the chapter as ap- but because anatomical clues may also provide insight about propriate. the etiology of the ocular motility disturbance. Indeed, many patients who present with concerns about ocular misalign- ment actually have pseudostrabismus because of an illusion 1.1 The Ocular Adnexa created by normal and abnormal ocular adnexa. Additionally, unwanted lid fissure changes induced by strabismus surgery are not uncommon because of the close anatomical relation- 1.1.1 Surgical Access ship between the extraocular muscles and eyelid structures. The implications for changes in eyelid shape and/or position following strabismus surgery should be clearly understood, Rarely does the shape or size of the palpebral fissures signifi- and reviewed with patients preoperatively, when applicable. cantly alter the surgical approach for strabismus surgery. How- While the conjunctiva is often inappropriately considered ever, small palpebral fissures and deeply set eyes can make sur- to be little more than a structure that must be incised to gain gical access more difficult. Recognition of these features prior surgical access to the extraocular muscles, an understanding to surgery can be important in helping the surgeon to estimate and recognition of key features of the conjunctival anatomy, es- the amount of time the procedure will take and in determin- pecially nasally, is necessary to devise and carry out appropri- ing the skill level of the surgical assistant that is needed during ate conjunctival incisions to optimize access to the extraocular surgery. Surgical access is most likely to be compromised when muscles, to assure proper conjunctival closure and good cos- performing large recessions on the medial rectus muscles of mesis following surgery, and to avoid scarring and contracture small infants and when operating on elderly patients with sig- of the conjunctiva which can produce unanticipated restric- nificant lid fissure abnormalities and deeply set eyes as a result tive strabismus postoperatively. We have encountered many of orbital fat atrophy. While these anatomical issues should not patients who have obtained good alignment following strabis- deter the surgeon from performing surgery, they may impact mus surgery but who were unhappy with the results of surgery the surgical plan. A limbal incision, which provides broad, un- because of the appearance of their conjunctiva afterwards. impeded access to the extraocular muscles for example, may be Tenon’s fascia and other orbital tissues have a direct im- a good option to facilitate surgery in the two examples cited. pact on the function of the extraocular muscles and on ocular Just as small palpebral fissures and deeply set eyes may limit alignment, both by helping to direct and alter the paths of the surgical access, prominent eyes, and wide palpebral fissures extraocular muscles through the formation of soft tissue pul- may facilitate access. Proptosis in a patient with thyroid-re- 4 Surgically Important Anatomy Chapter 1 lated ophthalmopathy may be associated with greater ocular The recognition of atypical strabismus in a patient with a cra- discomfort and a greater risk for exposure keratopathy follow- niofacial abnormality may prompt consideration of neuroim- ing surgery. aging studies to evaluate for abnormalities in muscle positions within the orbit, absent muscles, and other abnormalities [2] (Chap. 27). 1.1.2 Eyelid Fissure Orientation 1.1.3 Facial Asymmetry Careful analysis of the ocular adnexa can provide import clues as to the etiology of strabismus in some patients and may help guide preoperative evaluation and surgical management. For Facial asymmetry has been reported in association with con- example, strabismus is not only common in patients with cra- genital superior oblique palsy [3, 4]. It is manifested as midfa- niofacial syndromes, but it is often atypical, involving both cial hemihypoplasia on the side of the face in the direction of horizontal and/or vertical deviations and is commonly associ- the head tilt. Thus it most commonly is seen on the side of the ated with marked overaction and/or underaction of the oblique face opposite the superior oblique palsy. The nose and mouth muscles that may be secondary to incyclorotation or excyclo- are typically deviated toward the hypoplastic side of the face rotation of the globe in these cases or due to the absence of one (>Fig. 1.2). This facial asymmetry is thought to be associated or more oblique muscles and/or tendons, most commonly the with congenital and early-onset superior oblique palsies. This superior oblique tendon. A combination of several different facial asymmetry has been postulated to occur as a result of factors may lead to the development of strabismus in patients a chronic head tilt from a young age [5] though others have with craniofacial syndromes. Recognizing that the patient has questioned its association at all [6]. Many strabismus surgeons strabismus due to a craniofacial skeletal abnormality should believe that the presence of facial asymmetry as characterized prompt the surgeon to carefully evaluate for an A- or V-pat- above and/or the presence of a chronic head tilt in a patient tern, oblique muscle dysfunction, and other disturbances. with a recently diagnosed superior oblique palsy is sufficient Often the facial features of a patient with a craniofacial ab- evidence to warrant a diagnosis of congenital or early-onset normality will be subtle, but may still have an important im- superior oblique palsy, negating the need for neurologic evalu- pact on both the etiology and treatment of strabismus. In gen- ation. Patients with congenital superior oblique palsy are of- eral, patients with significant down-slanting palpebral fissures ten found to have a “floppy” or otherwise abnormal superior tend to demonstrate apparent inferior oblique overaction dur- oblique tendon at surgery [7]. This finding may help to dictate ing adduction and may have V-pattern strabismus (>Fig. 1.1), the surgical approach used in these patients. while those with up-slanting palpebral fissures tend to dem- Patients with unilateral coronal synostosis (plagiocephaly) onstrate apparent superior oblique overaction during adduc- often present with an ocular motility condition that clinically tion and may have A-pattern strabismus. Patients with spina resembles superior oblique muscle palsy. The apparent “palsy” bifida, for example, commonly have A-pattern horizontal stra- is due to asymmetric orbital growth. The trochlea on the in- bismus in association with up-slanting palpebral fissures [1] volved side does not advance anteriorly as would occur in a (>Fig. 1.1). Anatomical variation in paths of the extraocular normal orbit where it ultimately is located anterior to the equa- muscle through the orbit have been shown to be altered and tor of the globe. The resulting position of the trochlea more heterotopia of rectus muscle pulleys has been implicated as the posterior than normal relative to the equator of the globe re- cause of A-pattern horizontal strabismus in these patients [1]. sults in a reduction of depressing action during contraction Fig. 1.1a,b. Lid fissure anatomy may provide initial clues in evaluat- ing a patient with strabismus. a V-pattern strabismus and apparent inferior oblique overaction in a patient with down-slanting palpebral fissures. b A-pattern strabismus is common in patients with up-slant- ing palpebral fissures 1.1 The Ocular Adnexa 5 gist may be the first physician to recognize the presence of the condition, prompting referral to a neurosurgeon for surgical treatment. Flattening of the forehead and mild to moderate prominence of the eye resulting from the presence of a shallow orbit on the involved side, and skull asymmetry are notewor- thy findings in these patients. Neurosurgical treatment of coronal synostosis may alter ocular alignment, changing the ultimate surgical plan, or even eliminating the need for strabismus surgery altogether.