Strabismus surgery

Chapter 85 Strabismus surgery





Introduction


The management of strabismus involves careful assessment of patients, and various forms of treatment, including correction of refractive error, orthoptics, amblyopia therapy, and surgery. Amblyopia should generally be treated prior to performing strabismus surgery.


The goals and risks of surgery should be clearly delineated to the parents, the child, and in the case of adults with strabismus, the patient. Parents should understand the importance of ongoing follow-up, particularly during the period of visual development, which extends through roughly the first decade of life.


The evaluation of surgical patients should include historical information, such as age of onset, direction of the strabismus, changes in the strabismus magnitude or direction over time, prior non-surgical or surgical treatment, and family history. A comprehensive ophthalmologic evaluation is essential, including cycloplegic refraction. Visual acuity should be documented at near and distance with appropriate correction. Refractive error should be fully corrected prior to determining the angle of deviation. The current prescription needs to be measured and, if a prism is present, this should be noted.


An appropriate sensory and motor examination is important. Sensory examination should include tests of fusion and stereopsis in patients old enough to perform them. In older children as well as adults with incomitant strabismus and diplopia, a diagram of the field of single binocular vision may be included. Motor examination is tailored to the unique features and age of the patient. Complex, multiplanar non-concomitant strabismus with limited range of movement requires special attention. A diagram of ocular range of motion for both ductions and versions is helpful.


In patients with prior ocular surgery, anterior segment and retinal findings may influence the choice and technique for surgery. Examination should identify conjunctival surgical scars and, the status of anterior ciliary vessels over the rectus tendons and insertions. Chorioretinal scars from prior surgery should be identified before additional strabismus surgery is performed.



Anatomy is important to strabismus surgery



Conjunctiva


The conjunctiva is a thin mucous membrane comprising the external surface of the eye posterior to the limbus. The conjunctiva fuses with Tenon’s capsule and intermuscular septum 1 mm posterior to the limbus. This zone of fusion is useful during traction testing and when positioning the eye with forceps during surgery. Posterior to the zone of fusion, the conjunctiva can be separated from the underlying Tenon’s capsule.


The conjunctiva is nearly transparent and well vascularized (Fig. 85.1). Adjacent to the limbus, it contributes to the rich anastamotic vascular network providing collateral flow to the anterior segment.1 After topical 2.5% phenylephrine, normal conjunctival vessels constrict; the underlying anterior ciliary vessels do not. The anterior ciliary vessels, their scleral penetration sites and anastamotic branches to neighboring rectus muscles can be seen. The insertion sites of the four rectus muscles can be visualized. The anterior termination of the extraconal fat pad is seen through the conjunctiva roughly 10 mm posterior to the limbus. These features help determine if there has been prior surgery and guide placement of the surgical incision.



The conjunctiva permits full movement of the globe. With scarring the conjunctiva can limit globe movement.



Tenon’s capsule


Tenon’s capsule is a dense, translucent and nearly avascular fascial layer extending from the limbus to the optic nerve. Anteriorly, it is located just beneath the conjunctiva. The conjunctiva can easily be separated from the underlying Tenon’s capsule, beginning 1 mm posterior to the limbus. Three millimeters posterior to the limbus, Tenon’s capsule fuses with the underlying intermuscular septum, forming a single fascial layer.2 Posterior to this zone, Tenon’s capsule envelops the globe, forming a potential cavity (sub-Tenon’s space).


In young people, Tenon’s capsule is thick, white and glistening, becoming thinner in adulthood. The bulbar surface of Tenon’s capsule is smooth, providing movement of one fascial plane over another.


Tenon’s capsule is penetrated by the four rectus muscles, just posterior to the equator of the globe. The penetration sites are approximately 10 mm posterior to the insertion of the rectus muscles. The inferior oblique muscle and superior oblique tendon penetrate Tenon’s capsule just anterior to the equator. The penetration sites of the extraocular muscles resemble a cuff on the sleeve of a sweater and represent a point of attachment between Tenon’s capsule and the capsule of the four rectus muscles, the inferior oblique muscle, and the superior oblique tendon. This point of attachment is an important landmark during strabismus surgery and in the recovery of lost muscles.


The penetration sites of the rectus muscles form a division between anterior and posterior Tenon’s capsule. Anterior Tenon’s capsule extends from the penetration sites to the limbus, while posterior Tenon’s capsule extends from the penetration sites to the optic nerve.


Tenon’s capsule separates the orbital fat from the globe. Anterior Tenon’s separates extraconal fat from the eye; posterior Tenon’s separates intraconal fat from the globe. Fibrous septae extend from the outer surface of Tenon’s capsule to the orbital periosteum.3 It is important to avoid violating Tenon’s capsule during surgery. Failure to do so permits fat to prolapse into sub-Tenon’s space. Scarring may result in fat adherence with restricted eye movement.



Muscle capsule and intermuscular septum


The rectus and oblique muscles and tendons are enveloped in connective tissue capsules. The capsules on the rectus muscles are well developed anterior to the site of the muscles’ penetration of Tenon’s capsule. With age, the capsules thin. Postoperative scarring is reduced if the muscle capsule is left intact in areas not involved with the procedure. Posterior to the penetration site in Tenon’s capsule, the muscle capsules become quite thin.4


The intermuscular septum is a thin, avascular layer of connective tissue that is continuous with the muscle capsules, extending from the border of each rectus muscle to the adjacent rectus muscles (Fig. 85.2). Anterior to the rectus muscles’ penetration of Tenon’s capsule, the intermuscular septum forms a thin, separate layer just beneath Tenon’s capsule, adjacent to the sclera. Posterior to the rectus muscles’ penetration, the intermuscular septum has been thought to separate intraconal from extraconal fat. However, the existence of this portion of the intermuscular septum has recently been questioned: it may be the anterior aspect of the connective tissue pulleys.5 The intermuscular septum is associated with the inferior oblique and forms a roughly 2 mm wide band, extending off the posterolateral margin of the muscle.




Blood supply


The ophthalmic artery supplies the extraocular muscles. The lateral muscular branch of the ophthalmic artery supplies the lateral rectus, superior rectus, superior oblique, and levator palpebrae superioris. The lateral rectus is also supplied by the lacrimal artery. The medial muscular branch of the ophthalmic artery supplies the inferior rectus, medial rectus, and inferior oblique muscles. The inferior rectus and inferior oblique muscles are also supplied by the infraorbital artery.


Each of the four rectus muscles carries anterior ciliary vessels that contribute to the blood supply of the anterior segment; the two oblique muscles do not. In the classic description, each rectus muscle has two anterior ciliary arteries, except the lateral, which has one.6 This diagram of the ocular circulation is reproduced repeatedly in ophthalmic literature6,7 and shows the anterior ciliary vessels traveling within the muscle and tendon. However, the vessels emerge from the substance of the muscle, posterior to the transition from muscle to tendon, and travel on the surface of the tendon8 (Figs 85.3 and 85.4). The number of anterior ciliary vessels is variable.9,10




The contribution of the anterior ciliary vessels to anterior segment blood flow has been studied by iris fluorescein angiography.11 Tenotomy of either of the vertical rectus muscles produces a significant delay in vascular filling in the corresponding segment of the iris.12 Surgery on the vertical rectus muscles impacts more on anterior segment blood flow than surgery on the horizontal rectus muscles and may influence the risk of anterior segment ischemia.





Pulleys of the orbit


Highly complex pulleys in the anterior orbit have been described. Each rectus muscle passes through an encircling ring of connective tissue near the equator of the globe, which attaches to the orbital wall. The pulleys are composed of collagen, bands of smooth muscle, and elastin.13,14 They have an intimate and active relationship with the extraocular muscles, which can include acting as the functional origin and limiting side-slipping.15,16,17 Orbital malformations, disease, trauma, and surgical procedures that affect the integrity of the orbital pulleys may be significant in ocular motility disorders.



Rectus muscles


There are four striated rectus muscles arising from the annulus of Zinn in the apex of the orbit. Each is 40 mm in length and inserts on the sclera anterior to the equator of the globe. Following the “spiral of Tillaux,” the medial rectus inserts 5.5 mm from the limbus, the inferior rectus 6.5 mm, the lateral rectus 6.9 mm, and the superior rectus inserts 7.7 mm from the limbus (Table 85.1). The location of the insertions is actually somewhat variable.18 The insertions of the rectus muscles are curvilinear, particularly the vertical rectus muscles, in which the temporal border is further from the limbus than the nasal border.



The medial rectus is responsible for adduction, the lateral rectus for abduction. The superior rectus supraducts and the inferior rectus infraducts; they have additional actions − adduction and torsion.


The medial rectus muscle courses anteriorly along the medial wall of the orbit inserting on the sclera with a 6 mm arc of contact with the globe. It is at risk for inadvertent damage during ethmoid sinus procedures and nasal pterygium excision. Without fascial attachments to an oblique muscle and its innate tension and relatively short arc of contact, the medial rectus is at the greatest risk of inadvertent loss during surgery.


The lateral rectus courses anteriorly along the lateral orbit inserting on the sclera with a 10 mm arc of contact with the globe. The insertion of the inferior oblique is in close proximity to the lower border of the lateral rectus, 8−10 mm posterior to the lower pole of the lateral rectus insertion. Due to fascial attachments between the lateral rectus and the inferior oblique, the surgeon can often locate the lateral rectus muscle if it becomes detached during surgery or trauma.


The inferior rectus muscle courses anteriorly, laterally, and inferiorly to insert on the sclera. The inferior rectus forms a 23° angle with the visual axis when the globe in the primary gaze position. It has fascial attachments to the inferior oblique muscle and the lower eyelid retractors (Fig. 85.5). If these attachments are not severed during recession or resection of the inferior rectus, eyelid fissure changes may occur. Connective tissue attachments between the superior rectus and the superior oblique may assist the surgeon in locating a ‘lost’ superior rectus muscle.



The superior rectus muscle courses anteriorly, laterally, and superiorly to insert on the sclera. It forms a 23° angle with the visual axis when the globe is in the primary gaze position. The superior rectus has fascial attachments to the superior oblique tendon and the levator palpebrae muscle. If the attachments to the levator palpebrae are not severed during recession or resection of the superior rectus, eyelid fissure changes may occur. Connective tissue attachments between the inferior rectus and the inferior oblique may assist the surgeon in locating a “lost” inferior rectus muscle.



Superior oblique muscle


The actions of the superior oblique are incyclotorsion, depression, and abduction. The superior oblique is an antagonist of the inferior oblique, with respect to torsion. The other actions are not strictly antagonistic with the inferior oblique.


The superior oblique muscle arises from periosteum in the orbital apex above the annulus of Zinn and travels anteriorly along the superomedial orbital wall. It becomes a cord-like tendon, passing through the trochlea to run in a posterolateral direction at an angle of approximately 51° to 54° with the sagittal plane. The tendon passes under the superior rectus and fans out, inserting on the sclera in the superotemporal quadrant (Fig. 85.6). The anterior pole of its insertion is located close to the lateral border of the superior rectus, beginning 4 to 6 mm posterior to the superior rectus insertion. Its tendon is thin and broad, extending posteriorly for about 11 mm, but with considerable variability. The posterior end of the insertion lies 6−7 mm from the optic nerve. The superior temporal vortex vein can exit the sclera temporal to the superior oblique insertion, under the insertion or sometimes split the fibers of the insertion and pass through them.



The superior oblique tendon can be abnormal.19 It may be redundant, lax, or misdirected. It can have an anomalous insertion nasal to the superior rectus or may insert into Tenon’s capsule and the trochlea, or be absent.20 Intraoperative “exaggerated”21,22 traction testing of the superior oblique can demonstrate laxity of the superior oblique tendon (Fig. 85.7).



The nasal aspect of the superior oblique tendon has fascial relationships with the intermuscular septum, which envelops it to form a capsule. If the nasal intermuscular septum is thin, atrophic, or is damaged while performing a nasal tenotomy, the cut ends of the tendon may separate excessively, creating a superior oblique palsy. The ends of the tendon may be difficult to recover. There is a frenulum between the capsule on the underside of the superior rectus and superior surface of the superior oblique tendon. The frenulum must be lysed for significant procedures on either muscle (Fig. 85.8).




Inferior oblique muscle


The actions of the inferior oblique are excyclotorsion, elevation, and abduction. The inferior oblique forms an antagonist pair with the superior oblique with respect to torsion. The additional actions of the inferior oblique are not strictly antagonistic with the superior oblique.


The inferior oblique muscle originates from the maxillary bone adjacent to the lacrimal fossa. It passes posteriorly and laterally, forming approximately a 51° angle with a sagittal plane passing through the origin of the muscle. After passing beneath the inferior rectus, the inferior oblique travels upward inserting on the sclera, close to the macula.23 The tendon of the inferior oblique is 1−2 mm long, the shortest of the extraocular muscle tendons. The inferior oblique insertion is 8 to 12 mm posterior to the lateral rectus insertion, adjacent to its lower border. There is considerable variability in the location and configuration of the inferior oblique insertion.


The inferior temporal vortex vein lies close to the inferior oblique. It can be damaged when the surgeon isolates the inferior oblique muscle or when placing an inferior oblique muscle to be recessed at its new insertion site, which may be close where the vortex vein exits the sclera. The scleral exit of the inferior temporal vortex vein is variable, but is often close to the lateral border of the inferior rectus, 8−10 mm posterior to the lateral pole of the inferior rectus insertion.


The neurovascular bundle enters the inferior oblique muscle as it passes beneath the inferior rectus muscle. The neurovascular bundle may serve as the effective origin of the inferior oblique, particularly after anterior transposition of the muscle.24


Overaction of the inferior oblique is common, particularly in congenital esotropia, intermittent exotropia, and superior oblique palsy. Overaction of the inferior oblique is clinically graded on a scale of 1−4.25 Overaction of the inferior oblique must be distinguished from other causes of elevation of the globe in adduction. Overaction of the inferior oblique commonly coexists with dissociated vertical deviation.26



General principles of surgery








Traction testing


Traction testing is performed at the beginning of every procedure. If abnormal, the test may be repeated several times intraoperatively as the muscles are released. The position of the surgeon should be consistent for each traction testing. Traction testing consists of two components: force generation and passive range of motion.


Force generation testing is performed with the patient awake and able to follow commands, with no anesthetic induced akinesia or hypokinesia of the extraocular muscles. It qualitatively assesses the strength of the extraocular muscles by stabilizing the globe in one position and asking the patient to voluntarily move the eye in specific directions.


Passive range of motion testing can be performed in the office or the operating room. It qualitatively assesses the resistance imparted by the extraocular muscles as well as orbital tissues during manual rotation of the globe. It can be performed with the patient awake or under general or local anesthesia. The “volume effects” of any anesthetic agent injected in the orbit may alter the passive range of the traction test.


Intraoperative traction testing can be performed using different techniques. Most commonly, it is performed with two toothed forceps placed 180° apart adjacent to the limbus. The rectus muscles are evaluated by rotating the globe medially, temporally, superiorly, and inferiorly, while placing gentle anterior traction on the globe, to place tension the rectus muscles.


To test the oblique muscles, the globe is rotated into extorsion and intorsion with gentle posterior pressure on the eye (retropulsion). This places the oblique muscles, with their anterior functional origins, under tension.


The exaggerated traction test of the superior oblique determines whether superior oblique laxity is present and may be helpful in Brown’s syndrome.32 It is performed by grasping the eye with two toothed forceps adjacent to the limbus. The eye is adducted while placing the eye in retropulsion, external rotation, and elevation. While maintaining this position, the eye is moved into abduction. A palpable “thump” is perceived with a normal superior oblique. An absent or reduced “thump” is evidence of superior oblique laxity. This test requires a considerable experience.



Incisions for strabismus surgery




Fornix or cul-de-sac incision


The fornix or cul-de-sac incision is also commonly employed. It reduces postoperative discomfort and places the surgical scar is beneath the eyelid (Fig. 85.14). It requires a skilled assistant, familiar with ocular anatomy.



The fornix incision does not gain direct access to the sclera by penetrating the conjunctiva, Tenon’s capsule, and intermuscular septum together in a single incision. Proper placement is important, particularly to avoid bleeding, inadvertent entry into the orbital fat, and, potentially, surgery on the wrong muscle.


The conjunctiva is opened as an isolated layer. Depending on the location of the anterior termination of the extraconal fat, the incision is placed 1−2 mm anterior to the fornix extending for 8 mm parallel to the fornix. A second incision is made through Tenon’s capsule and the underlying intermuscular septum at a right angle to the conjunctival incision. It is important to avoid extending the incision in Tenon’s capsule more than 10 mm posterior to the limbus, due to the anterior border of the extraconal fat. When the sclera is exposed, a muscle hook is used to engage the extraocular muscle to be operated.


Fornix incisions may be performed in any of the four oblique quadrants. By employing only an inferior temporal and superior nasal incision, the surgeon can gain access to all six extraocular muscles. Avoid incising the plica semilunaris when performing an inferonasal quadrant fornix incision.



Swan incision


The Swan incision is made directly over the rectus muscle insertion.33 It is less popular due to the interpalpebral location of the wound with scar formation and potential bleeding from the underlying anterior ciliary vessels. A modified Swan incision may be useful in reoperations.




Extraocular muscle surgery





Tissue adhesives


Tissue adhesives have been used in conjunctival closure during strabismus surgery37,38 but have not gained popularity in securing the muscles to the sclera.3941




Rectus muscle surgery


Proper exposure of the extraocular muscles is essential for successful strabismus surgery. Dissection of excess connective tissue at the suture line provides better exposure for precise suture placement and decreases the risk of slipped or lost muscles (Fig. 85.15). This requires excision of redundant muscle capsule and intermuscular septum. The muscle capsule and intermuscular septum can be lifted off the rectus muscle adjacent to the insertion and excised without disrupting the anterior ciliary vessels. Cauterizing anterior ciliary vessels prior to passing sutures or making incisions in the tendon or muscle reduces bleeding and decreases scarring.




Weakening procedures on the rectus muscles



Recessions


Recessions are the most common weakening procedure on the rectus muscles. The maximal effect is in the field of action of the recessed muscle. However, recessions also have a significant effect on primary gaze alignment. Recessions are generally more comfortable postoperatively than resections; causing less swelling, dellen formation, inflammation, and scarring.


Recession results in a small resection of tendon. The method and point of measurement for recessions varies. Because of this and other factors, a 5 mm recession performed by one surgeon is not identical to one performed by another. Suture placement 1 mm posterior to the insertion minimizes the concurrent resection and allows disinsertion to be performed without inadvertent suture transection. Techniques to place the suture securely in the tendon include placement of a central tie in the tendon and double locking sutures at each border of the tendon.


The preferred site for measuring a recession varies. Measurement from the limbus avoids the potential variability in the position of the muscle insertion.42 Those who measure from the insertion of the tendon feel the amount of recession is dependent upon the change in position relative to the original scleral attachment point, rather than the limbus. Measurement from the insertion should be determined prior to disinsertion; the elastic properties of the sclera allow the insertion to shift anteriorly following detachment of the muscle,43 especially with tight extraocular muscles.


Recessions can be performed by attaching the muscle to the sclera at the desired position or by employing “hang-back,” “hemi hang-back,” or various modifications.


Direct fixation of the recessed muscle to the sclera is widely used (Fig. 85.16A,B). The scleral entry position of the needles is at the location of the desired recession and should be directly posterior to the original insertion site. Each pole should be spaced to maintain the width of the recessed muscle to avoid “central sag.” If sagging occurs, the center of the muscle can be sutured to the sclera (Fig. 85.17). Because the muscle is sutured directly to the sclera, it allows accurate supra- and infraplacement and “slanting” the recession, if desired, in “A” and “V” patterns.




Hang-back and hemi hang-back techniques are commonly employed in recessions (Fig. 85.16C,D).The hang-back technique suspends the muscle on a suture attached at or near the terminal poles of the original insertion or can be located near the mid-portion of the original insertion (see Fig 85.20). Hang-back recessions may reduce scleral perforations by placing the sutures in thicker sclera at the original insertion. However, with large recessions, the muscle may side-slip or creep anteriorly during or after surgery; this is reduced by placing shallow scleral “belt-loops” close to the recessed muscle or using an anchored hang-back suture (Figs 85.16E and 85.18).



In the hemi hang-back technique, the suture engages the sclera posterior to the original insertion site but anterior to the recessed muscle (Fig. 85.16D). Indications include: surgical exposure, thin sclera, scarring, the presence of an oblique muscle (particularly the superior oblique tendon), or a scleral buckle, glaucoma implant or other device on the sclera. Hemi hang-back sutures with large recessions may reduce the potential for side-slipping or muscle creep.


In a loop recession, a non-absorbable suture is placed through each pole of the muscle and sutured to the sclera behind the insertion (Fig. 85.16F).



Horizontal muscle recession


Dose-response tables for horizontal rectus recessions and resections are available. As a general rule, the medial rectus can be recessed a maximum of 7 mm without reducing adduction and the lateral rectus recessed up to 10 mm. Exceptions to these limits are common, particularly with restrictive and paretic strabismus, when much larger recessions are commonly employed. However, 7 mm bilateral medial rectus recessions may increase the risk of consecutive exotropia in children with congenital esotropia.4446 The dose-response with large recessions is non-linear and less predictable. The guideline values listed in the dose-response tables are most useful in uncomplicated strabismus (Tables 85.2 and 85.3).




The quantity of surgery required to correct horizontal deviations is dependent upon a number of factors, especially the magnitude of the preoperative deviation. Axial length and refractive error are not usually significant.47 Recession of unoperated rectus muscles is more predictable than recession of previously operated muscles. Restrictive disorders, particularly thyroid orbitopathy, and recession of antagonist to a paretic muscle are associated with a reduced effect per millimeter of recession. Very large recessions combined with resections may result in limitation of movement.


Recessions can be measured using a curved ruler or calipers. Curved rulers follow the circumference of the sclera, measuring the length of the arc (Fig. 85.19). Calipers measure the length of the chord: this disadvantage can be reduced by measuring the total recession as two small chord lengths, whose sum is equal to a large recession.




Inferior rectus muscle recession


Inferior rectus recessions are employed in complex non-concomitant vertical strabismus. Indications for inferior rectus recession include thyroid orbitopathy, blowout fracture, congenital fibrosis of the extraocular muscles, “double elevator” palsy, superior rectus palsy, superior oblique palsy in the contralateral eye, and anesthetic block induced vertical strabismus.


Recession of the superior rectus in the contralateral hypertropic eye is often preferred over recession of the inferior rectus in the hypotropic eye in non-restictive strabismus. In patients with over 15 prism diopters (PD) of deviation, recession of the ipsilateral inferior rectus and contralateral superior rectus can be considered.


Although inferior rectus recessions employ basic techniques similar to horizontal recessions, there are several differences. The inferior rectus is closely associated with the inferior oblique muscle and the retractors of the lower eyelid.


There are no dose-response tables for vertical rectus recessions or resections. On average, 1 mm of inferior rectus recession will result in correction of 3 PD of vertical deviation in primary gaze and 5 PD in downgaze.48


Recessions of the inferior rectus for non-paretic, non-restrictive disorders should generally be limited to 5 mm or less; larger recessions commonly cause lower eyelid retraction. However, inferior rectus recessions of less than 5 mm may cause lower eyelid retraction in restrictive strabismus, particularly thyroid orbitopathy. Severe restrictive disorders often require large recessions resulting in significant retraction of the lower eyelid. The patient should be warned of this preoperatively.


Techniques to reduce lower eyelid retraction include:



Delayed overcorrection is a significant problem following inferior rectus recession. This is usually accompanied by limited depression in the operated eye with diplopia, particularly in downgaze. Delayed overcorrection is more likely to occur with thyroid orbitopathy treated with adjustable sutures. It occurs in 10−21% of cases.52,53,54


A number of mechanisms may contribute to “late slippage” of the inferior rectus.55,56,58 These include:



Undercorrections after inferior rectus recessions are associated particularly with restrictive processes and reduced contractility of the opposing superior rectus. In severe thyroid orbitopathy, even recessions of 15 or more millimeters from the insertion may fail to correct the hypotropia. Significant restriction in elevation may persist, even while the inferior rectus is disconnected from the globe during surgery. Postoperative undercorrection in primary gaze with hypertropia in downgaze indicates a tight superior rectus. Restriction following orbital blowout fractures frequently is associated with alterations in the elastic properties of the surrounding orbital tissues.


Poor or absent superior rectus function is a cause for undercorrection. “Double elevator” palsy and superior rectus palsy are likely to be undercorrected with inferior rectus recessions alone. Failure of superior rectus development in congenital fibrosis of the extraocular muscles causes disappointing results following inferior rectus recession.60,61 Retrobulbar and peribulbar block induced vertical strabismus can be complex and is often associated with paretic and restrictive components.6267


Bilateral recessions of the inferior rectus muscles can create exotropia in downgaze, forming an “A” or “λ” pattern, especially in thyroid orbitopathy where large inferior rectus recessions have been performed. Nasal displacement of the inferior rectus muscles reduces the tendency for exotropia in downgaze. However, this may be associated with intorsion.63



Superior rectus muscle recession


There are also no dose response tables for superior rectus recessions or resections. Each millimeter of superior rectus recession generally corrects 3 to 4 PD of vertical deviation up to 6 mm of recession. Recessions of greater than 6 mm are avoided, except in dissociated vertical deviation (DVD), when hang-back recessions of up to 10 mm may be performed (Fig. 85.20).64,65 Superior rectus recessions beyond 4 mm require lysis of the fascial attachments between the underside of the superior rectus and the superior oblique tendon (see Fig. 85.8B). For very large recessions, it is important to dissect and cut fascial attachments and check ligaments on the superior rectus as far posteriorly as possible and identify the superior oblique tendon, both nasal and temporal to the superior rectus. The superior oblique insertion is in close proximity to the temporal border of the superior rectus. The thin fibers of the superior oblique near its insertion can be mistaken for intermuscular septum and inadvertently transected (Fig. 85.6).



Superior rectus recessions do not commonly cause upper eyelid retraction.66 Because of the potential problems associated with inferior rectus recessions, surgery for concomitant vertical deviations of up to 15 PD is often performed by superior rectus recession in the hypertropic eye.


Non-concomitant hypertropia that increases on downgaze is usually treated by recession of the ipsilateral superior rectus. In the absence of oblique dysfunction, hyperdeviations that increase in abduction are treated by superior rectus recession in the hypertropic eye. However, hyperdeviations that increase in adduction (without oblique dysfunction) are commonly treated by recession of the inferior rectus of the hypotropic eye. Deviations larger than 15 PD in primary gaze are often treated with recession of the superior rectus in the hypertropic eye and recession of the inferior rectus in the hypotropic eye.


Jun 4, 2016 | Posted by in OPHTHALMOLOGY | Comments Off on Strabismus surgery
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