Ординатура / Офтальмология / Английские материалы / Pediatric Ophthalmology Current Thought and A Practical Guide_Wilson, Saunders, Trivedi_2008

Contents

11.3Examination  . . . . . . . . . . . .   143

11.5Preoperative Discussion  . . . . . . . .   143

11.7Surgical Repair  . . . . . . . . . . .   144

11.8.1Stretched Scar  . . . . . . . . . . . .   145

11.9.1Partial Avulsion of a Rectus Muscle

(Flap Tear)  . . . . . . . . . . . . .   146

11.9.2Lost Muscle   . . . . . . . . . . . .   148

Core Messages

•Perform a thorough history. Most of the information needed to manage complex strabismus is obtained by the history.

•Keep an open mind until the diagnosis is certain. Do not try to fit the patient into your first diagnostic impression.

•Allow time for thorough evaluation, and measure ocular motility yourself.

Schedule a return office visit, if necessary.

•Additional diagnostic tests are selectively chosen as needed; orbital CT scan to rule out fracture, chronic sinusitis and view extraocular muscles, MRI scan of brain, tensilon test, laboratory tests for thyroid function, and rheumatologic disease.

•Final diagnosis may await the intraoperative assessment, including forced ductions to rule out fibrosis, restrictions, or weakness, and direct visualization of the extraocular muscles to rule out trauma, malposition, or healing abnormality following prior strabismus surgery.

•During surgery, be flexible in approach to allow for unexpected findings.After repair, use spring-back test to assure centration of the eye, and reposition muscle(s) if necessary. Use non-absorbable sutures when poor healing is suspected or

tendons are under high tension.

•Postoperatively tailor steroid use to the condition, and use adjunctive procedures such as motility exercise and in-office forced duction to expand range of motion.

11.1 Introduction

All strabismus cases require a thorough diagnostic approach, but some cases are unusually complex and those are the focus of this chapter. Some diagnoses may seem straightforward on initial impression, but due to incomplete information, complexities are overlooked, and outcomes are unsuccessful. Methodical acquisition of information combined with careful observation is the key to success. Complex cases are less daunting if they are approached methodically, and enough time is allotted to obtain an adequate history and complete exam. It may not be possible to achieve the full range of ocular motion in every patient, but just about every eye can be centered and many can have restoration of functional motility.

11.2 History

The patient’s history is the most important factor in diagnosis (footnote), yet we often allow little time for the history and proceed directly to the exam. In most cases the history will suggest the diagnosis provided that the correct questions are asked. Was the onset abrupt or gradual? Was there any trauma proceeding onset of symptoms? Patients usually need to be prodded on these questions, as they often forget seemingly minor, but significant, blunt trauma. When strabismus occurred due to trauma, was there loss of consciousness? How long? Was there facial trauma, skull or facial fracture, or ecchymosis? Did the face hit an air bag?

Is there a history of smoking, chronic disease, recurrent sinusitis, hyperflexibility, poor wound healing, or poor nutrition? Is the strabismus worse with fatigue or upper respiratory infection? Is there associated pain or eyestrain? Is there a family history of strabismus?

Acute onset of strabismus will occur with a vascular event, and the patient should be able to recall exactly when he or she first noticed symptoms. The entire motility deficit develops in one event, followed by stable alignment or gradual improvement, with vascular or traumatic cranial nerve paresis.

Subacute onset followed by stability of alignment is the usual time course of strabismus due to partial

avulsion of an extraocular muscle by blunt trauma (flap tear) [7, 8]. The motility deficit usually develops as the muscle fibroses to surrounding connective tissue. Subacute onset followed by progression of alignment abnormality would be the pattern usually seen with accommodative esotropia, intracranial compressive lesion, raised intracranial pressure, acute sinusitis, orbital myositis, orbital floor collapse, or some cases of thyroid ophthalmopathy.

Chronic, gradually progressive onset of strabismus is the most common form of acquired strabismus and the patient’s history of onset is usually vague. There may be years of prism wear with gradual increase until the prism requirement becomes too great and the patient is referred for surgery. Increasing head tilt or head turn may cause neck pain, prompting the patient to seek treatment. Old photographs may be needed to document the time of onset of head tilt or turn. Some patients notice periods of stability, with bouts of exacerbation, which they associate temporally with upper respiratory illness. Patients who have had successful alignment after prior strabismus repair may develop gradual consecutive strabismus from stretching of the scar between the sclera and muscle tendon, which may accelerate during bouts of illness, malnutrition, and pregnancy [6, 9]. Conditions that usually present with chronic onset include presumed sinus-related strabismus [10], myasthenia gravis, and slow-growing intracranial lesion. Some congenital syndromes, such as Duane’s syndrome and congenital fourth cranial nerve palsy, may deteriorate gradually. Consecutive exotropia in monofixation syndrome without prior strabismus surgery, and stretched scar due to prior strabismus repair [6, 9], usually have a slowly progressive time course. Extraocular muscle fibrosis syndromes, such as thyroid ophthalmopathy and chronic orbital myositis, may be gradually progressive.

Variable onset and variable expression of strabismus is seen in some patients with chronic strabismus and good fusional vergence ability. These patients may have symptoms that seem out of line with the minimal or no strabismus manifest in the office. For example, a child’s parent sees esotropia in the evening, but the office exam shows minimal esophoria.

An adult complains of severe diplopia but has minimal phoria on exam. The history can alert you to the possibility that strong fusional vergence is masking

the true deviation, and suggest the need to perform prism adaptation. Myasthenia gravis should always be considered in the differential diagnosis of acquired strabismus, especially when symptoms and alignment measurements show variability.

11.3 Examination

Measure motility carefully, including alignment in all directions of gaze, cover–uncover and alternate cover test and version testing. Stereopsis is measured as well as subjective torsion (double Maddox, Bagolini lens, or Lancaster red-green test), and objective torsion (dilated fundus exam).

The Parks’ three-step test [11] is a tool to identify a single paretic muscle. It does not apply to muscle fibrosis or direct muscle trauma. Fibrosis of an inferior rectus of one eye may produce the identical pattern on the three-step test result as superior oblique palsy in the contralateral eye. It is important to discriminate this for each patient. Mild extorsion in the lower eye, rather than marked extorsion in the higher eye, may be a clue that a fibrotic, rather than paretic, etiology is present. Forced duction may be needed to distinguish between the two. Large fusional vergence has traditionally been considered as diagnostic of a congenital paretic etiology but may also be present with vertical deviations of gradual onset.

In office prism adaptation is a useful tool to uncover the full deviation in patients with suspected large fusional vergence, and reduce the frequency of surgical undercorrection. The measured deviation is placed into trial frames with loose prisms and best correction (with near add if necessary). The patient reads for 20 min, the deviation is remeasured, and prism increased accordingly. This process is continued until a small deviation in the opposite direction is produced. The trial frames are then removed, and alignment testing is performed in all gaze directions both distance and near. This “adapted alignment” is used to calculate the surgical correction.

Repeat evaluation on a different date and preferably at a different time of day is useful when variability or active progression or regression is suspected, as with myasthenia gravis, evolving thyroid ophthalmopathy, or improving cranial nerve palsy.

11.4 Diagnostic Testing

If orbital disorder or thyroid ophthalmopathy are suspected by exam, imaging of the orbits may be needed.

A CT scan best demonstrates the bony orbits and sinuses, but intrinsic orbital lesion is better seen with MRI. Select the technique that corresponds to your leading differential diagnoses [2]. Laboratory tests may be performed to rule out thyroid dysfunction or rheumatologic disorder. Tensilon test should be performed if myasthenia gravis is suspected. Negative antiacetylcholine receptor antibody test is frequently negative in ocular myasthenia and is only helpful in diagnosis if positive.

Presumed sinus-related strabismus is a form of atypical acquired strabismus that may mimic cranial nerve palsy, high AC/A ratio, or thyroid ophthalmopathy [10]. Acute or chronic sinusitis may lead to adjacent fibrosis of the extraocular muscles and surrounding orbital tissues as well as secondary strabismus. Warning features include atypical age of onset, no family history of strabismus, normal refraction, and evidence for normal development of binocularity. Some patients relate the onset of strabismus to an upper respiratory infection, but others are unaware of sinus symptoms. If ongoing sinusitis is the cause of strabismus and is not treated, recurrence may occur despite good initial surgical correction. Sinus CT scan is the most accurate method to rule out sinus disease (Fig. 11.1). Sinus and nasopharyngeal carcinoma, mucoceles, and other sinus lesions are rare causes of gradually progressive strabismus, which will also be detectable by imaging.

Malposition of extraocular muscles may be congenital (orbital malformation, pulley abnormalities) or acquired (high myopia with lateral rectus displacement). Coronal sections on orbital CT or MRI scan will demonstrate these abnormalities [2].

11.5 Preoperative Discussion

Prior to undertaking surgery, discussion with the patient needs to stress that you are undertaking a reconstructive process, which may require multiple procedures to achieve final success. Most patients are relieved to learn that you are committed and will not

abandon their case if the first procedure is not fully satisfactory.

Patients may have systemic disease, which will influence surgical decision making, and they should be involved in any related discussion. Systemic anticoagulation will increase the risk of bleeding from local anesthetic injection, but that may be preferred rather than the increased risk of embolic event if anticoagulants are discontinued. Strabismus surgery under general anesthesia is usually possible with moderate anticoagulation, and this route may be preferred for some. Systemic disease may preclude general anesthesia in some patients, who may safely receive local anesthetic. Eyes with substantial deviations and increased fibrosis, such as post-retinal detachment or glaucoma surgery, are very difficult to operate with local anesthetic.

11.6 Intraoperative Assessment

Forced ductions are tested in all directions, including intorsion and extorsion, as well as exaggerated forced duction of the oblique muscles. The torsional forced duction test is performed with two forceps grasping the eye at the three o’clock and 9 o’clock positions.

The eye is then extorted and intorted while being gently proptosed. Normal rotation is 60–70º of extorsion and intorsion before resistance is met. Decreased

rotation may signify tightness of the anterior fibers of the oblique muscles, or abnormal adhesions between extraand intraconal tissues. The exaggerated forced duction test of the oblique muscles is performed with the eye gently retropulsed and provides information about the posterior fibers of the oblique muscles.

The next step is direct observation of the extraocular muscles by surgical exploration. If prior eye muscle surgery had been performed, the density of overlying scar tissue is assessed. Unusually light, non-adherent scar, with unusually easy dissection, suggests poor wound healing [6]. Measure the distance from the scleral point of attachment of each muscle to its original insertions. Compare that to previous operative reports to rule out scar migration (see later) [6]. Inspect the muscle for evidence of scar stretch [6, 9], slipped muscle [13], missing muscle tissue [7, 8], or erosion by retinal band. Dense scar tissue may indicate excessive inflammation or adhesive syndrome [12] due to posterior disruption of

Tenon’s capsule by prior surgery or trauma.

11.7 Surgical Repair

In general, the best initial approach is to directly repair the original cause of strabismus, such as reattaching a lost muscle or repairing a torn muscle. Other muscles are then operated as necessary to cor-

rect residual deviation. Examples include recessing a contractured antagonist muscle, or using a Faden suture in one eye to balance motility restriction in the other eye. Sometimes several procedures are performed simultaneously, if the need is obvious, but frequently the additional muscles are operated later, after the response to the initial procedure is gauged.

secting the minimal amount necessary to expose the muscle insertion and repair strabismus is a principle which will reduce restrictive strabismus complications. Conversely, when capsule disruption has occurred, direct repair is advisable.

11.8 Management of Scar Tissue

Scar tissue is obviously necessary to heal the operated extraocular muscle in its new position, but when scarring is excessive due to heavy-handed prior strabismus surgery, trauma, RD repair, etc., the scar tissue needs to be managed along with the muscles. Steroids will delay scar formation, but scarring will always eventually recur. It is better to control the position and direction of restriction generated by the scar rather than attempt to prevent scar from forming. Scar is first dissected free from the globe in order to operate on the muscle. If scar is neglected at this point, it will reform and often change an initially good alignment result. Instead, scar needs to be sutured directly to sclera using a fine-gauge absorbable suture, in a position where it will not interfere with the alignment outcome. This is a handy technique, and with practice, it can even be used to enhance the effect of the muscle surgery.

Tenon’s capsule and intermuscular septum allow normal sliding of orbital tissues and capsule disruption increases fibrosis and can restrict motility. Dis-

11.8.1 Stretched Scar

Consecutive strabismus following prior strabismus surgery is a common complication occurring in 2−8% of cases in which good initial alignment was achieved

[6]. In many of these cases, gradual lengthening of the scar between the sclera and muscle tendon has developed, causing the surgical over correction [6, 9]. Some limitation of motility in the direction of action of the involved muscle(s) may be seen, but this may be mild and is not always present, especially if the stretch is 3 mm or less. During initial dissection to isolate the muscle, scar tissue is surprisingly mild and easily stretched in these patients. Once hooked, the muscle can usually be lifted away from sclera with ease (Fig. 11.2). Recognition of the transition between scar and normal tendon may be difficult, as the scar assumes a striated appearance, which mimics tendon (Fig. 11.3). Knowledge of the normal tendon length for the muscle will help to guide the surgeon to the transition between normal tendon and scar. Non-absorbable suture is placed through secure tendon (Fig. 11.4), scar tissue anterior to the suture is excised, and the muscle securely sutured to sclera, using standard surgical tables as a guide to the best

Fig. 11.2  As muscle hook is pulled away from sclera, medial rectus stretched scar lifts upward

Fig. 11.3  Stretched scar of medial rectus. Arrows indicate transition between scar and tendon. Lower hook indicates scleral attachment site

Fig. 11.4 Stretched scar of inferior rectus. Braided polyester suture is placed through tendon, prior to excision of scar r. (Reproduced with permission from the Trans Am Ophthalmol Soc in Ludwig IH (1999) Scar remodeling after strabismus surgery. Tr Am Ophth Soc 92:583–651)

Stretched scar segment

A B

Fig. 11.5 Illustration of stretched scar repair calculation. Planned millimeters of resection/advancement from surgical tables =A+B. C–B = mm behind original insertion where sutures are placed

location to reattach the muscle (Fig. 11.5). Adjustable suture use increases the risk of stretched scar and is not recommended for these patients. Steroid use should be avoided, as it impedes wound healing. Patients are asked to avoid stretching the eyes into extremes of gaze for several months, and daily vitamin C supplementation is recommended.

Stretched scar cases were frequently confused with classic slipped muscles (see later) but have been documented to occur despite proper surgical technique, and to restretch frequently if absorbable sutures are used [6].

11.8.2 Scar Migration

When the operative report from prior strabismus surgery is available, it is sometimes observed that the extraocular muscle is attached at a position other than where it had been attached. Muscle scars under tension can migrate during the healing period. Migration of attachment position is commonly seen after Jensen,

Hummelsheim, and traditional Faden procedures [6].

This problem can usually be prevented by the use of non-absorbable sutures.

11.9 Other Complex Strabismus

Paralytic strabismus, Duane’s syndrome, and dissociated deviations may be complex. These are discussed in other chapters and will be omitted here. The slipped muscle, as described by Parks and Bloom [13], is similar in concept to stretched scar in that the tendon is not attached directly to sclera but is separated by a segment of other tissue − in this case a long segment of muscle capsule. This is defined as due to improper surgical technique, incorporating only capsule in the suture, which causes the muscle to retract posteriorly. The resultant deviation is large, occurs quickly in the postoperative period, and usually responds well to prompt repair with standard sutures.

Regarding partial avulsion of a rectus muscle (flap tear).

11.9.1Partial Avulsion of a Rectus Muscle (Flap Tear)

With blunt trauma to the face, partial avulsion of one or more rectus muscles may occur [7, 8]. Traction from the bending or fracturing orbital wall may pull

Fig. 11.6  Proposed mechanism of flap tear, showing traction on inferior rectus (arrows) during orbital fracture

Fig. 11.7  After tear has occurred, the flap heals to surrounding orbital connective tissue, restricting motion

on the orbital septae and tear the outer or orbital layer of the rectus muscle from the inner or global layer [3].

In other cases, perhaps due to sudden muscle contracture, a portion of the tendon is disinserted from the sclera (Fig. 11.6). This avulsed “flap” of muscle may then heal to surrounding orbital soft connective tissue leading to restrictive strabismus (Fig. 11.7). The motility defect may simulate muscle paresis, usually with decreased action of the involved muscle, due to a tether effect created by the scarred portion of avulsed muscle. Orbital fracture is frequently, but not always, present. Partial avulsions are also seen following retinal detachment repair and direct trauma to the muscle insertion.

The most common partially avulsed extraocular muscles are the inferior and medial recti, but superior and lateral rectus flap tears have been seen. The size of the avulsed flap is variable.

History is critical to flap-tear diagnosis. A patient with blunt head or facial trauma with no loss of consciousness may be more likely to have suffered direct muscle trauma rather than cranial nerve palsy. History of ecchymosis or periorbital edema is suggestive. Diplopia may be immediate, but usually does not develop until several weeks after injury, when

scar tissue begins to create restriction of gaze. Cranial nerve palsy due to head trauma from a motor vehicle accident is sometimes combined with flap tear caused by facial impact with an air bag.

Flap tears produce incomitant strabismus. The most common form is hyperdeviation greatest on downgaze due to partial avulsion of the ipsilateral inferior rectus. This may be confused with fourth cranial nerve palsy, which is ruled out by the lack of extorsion in the hyperdeviated eye. Inferior rectus paresis is ruled out by a normal inferior rectus force generation test. Bilateral inferior rectus flap tear may produce “A” pattern exotropia, convergence insufficiency, and vertical strabismus. Exotropia with convergence insufficiency has also been seen with medial rectus flap tears.

Orbital CT scans are useful to rule out orbital fracture, but traditional MRI scans are usually not helpful. Newer, high-resolution MRI scans, which produce images of the extraocular muscles in multi- ple-gaze positions, may eventually prove more useful to pinpoint the flap-tear abnormality [2].

To repair a partially avulsed rectus muscle, first review the anatomy and repair literature [7, 8]. Forced duction will usually demonstrate restriction toward

the field of action of the involved muscle movement of the eye, and torsional forced duction usually shows marked restriction to intorsion and extorsion, presumably due to the abnormal adhesion between the intraand extraconal spaces.

A standard inferonasal fornix incision allows inspection of both the inferior and medial recti. Disruption of the normal muscle capsule is an important clue to the presence of a flap tear; therefore, only the minimum dissection necessary to see the muscle should be performed. The attached portion of inferior rectus is placed on the muscle hook, and the

Desmarres retractor is used to expose the muscle, capsule, and intermuscular septum. The partial avulsion appears as either a narrowing of muscle width or muscle thinning. Both types show capsule disruption (Fig. 11.8). When in doubt, compare the anatomy by viewing the same muscle of the contralateral eye. The avulsed “flap” of muscle is found external to the Desmarres retractor and adherent to orbital connective tissue. The flap edge is freed from adhesions to surrounding tissue, attempting to preserve the avulsed capsule with the muscle flap. Tissue layers should be handled gently. Non-absorbable suture (braided 6-0 polyester) is placed through the distal end of the flap, with locking bites (Fig. 11.9). The flap is sutured to its normal anatomic position, directly to sclera. Capsule is repaired with running 8-0 polyglactin suture

(Fig. 11.10). If an external rent in Tenon’s capsule is present, with prolapsed orbital fat, the fat is reposited and the rent closed with 8-0 polyglactin.

If orbital fracture coexists with partial muscle avulsion, it may be repaired through a separate inci-

sion and on the same day, if possible. Best results have been obtained with muscle repair alone or simultaneous fracture and muscle repair. Patients with a significant delay between orbital fracture repair and muscle repair have worse results, perhaps due to orbital tissue fibrosis or secondary changes in antagonist muscles.

If flap tear is suspected by history and forced ductions, but cannot be located during surgery, it is best to resect the remaining attached portion of the involved muscle. This will reduce the flap’s tether effect. Recession of the antagonist muscle does not improve tether restriction but may be needed as a secondary procedure.

Postoperatively, exercise of motility in the involved gaze directions is critical to reduce the risk of restriction from to adhesions. The use of steroids could reduce adhesion formation, but as they inhibit healing of tendon to sclera, they are usually avoided.

11.9.2 Lost Muscle

Alost extraocular muscle has lost all direct or indirect connection to the sclera [14]. Most lost muscles occur during ophthalmic surgery while the muscle is under traction. Sometimes, in patients with weak connective tissue, the muscle may rupture at the musculo-tendi- nous junction. This is known as the “pulled-in-two syndrome” (PITS) [4]. The proximal portion of the muscle retracts posteriorly, and becomes “lost.” During strabismus surgery, the suture may pull through

the tendon after muscle disinsertion, thereby creating a lost muscle. Sinus surgery may lead to lost muscle, by eating away a portion of the muscle, and creating a lost proximal endas well as a length defect. In blunt trauma, the muscle may completely avulse from its insertion, without losing its attachments to intermuscular septum, and lost muscle may occur with direct penetrating trauma.

If the lost muscle retains its septal attachments to the oblique muscles, these can be traced back to the lost rectus muscle. This technique is useful for the inferior, superior, and lateral recti. The medial rectus lacks these indirect attachments and is therefore the most difficult muscle to recover when lost. It is

Fig. 11.9  Flap tear from muscle in Fig. 11.8 (right). Flap has been dissected free, and braided polyester suture has been placed through its distal end d. (Reproduced with permission from the Trans Am Ophthalmol Soc, in Ludwig IH, Brown MS

(2001). Strabismus due to flap tear of a rectus muscle. Tr Am

Ophth Soc 99:53–63)

sometimes possible to follow Tenon’s capsule posteriorly to the point where the medial rectus originally penetrated Tenon’s capsule to locate the lost muscle. Avulsed lost muscles are usually found near the globe and adherent to orbital soft connective tissue. When dehiscence at the musculotendinous junction has occurred, the torn tissue is fragile and lacks strength to support sutures. Repair is to the surrounding muscle capsule, which allows better support due to connective tissue in the capsule. It also reduces tension and vascular strangulation in the damaged muscle tissue.

Orthopedists use this principle in tendon repair [5].

Lost muscle following sinus surgery usually involves significant tissue loss, which prevents direct repair.

Non-absorbable sutures to bridge the gap may be used. If the lost muscle cannot be repaired, the antagonist muscle is weakened, and transposition of adjacent muscles is performed.

Thyroid ophthalmopathy patients are complex strabismus cases due to their frequently severe extraocular muscle fibrosis. Most patients will achieve almost full functionality if surgery is planned and executed carefully. The goal is always to obtain the best balance of alignment with as wide a field of single vision as possible while operating the least number of muscles possible. When there is a large vertical deviation, it is best to avoid a large recession of a single inferior rectus, which will restrict downgaze. Smaller recession of the inferior rectus combined with recession of the superior rectus of the contralateral eye (if it is intorted), or recession/anterior transposition of the inferior oblique of the contralateral eye (if it is extorted), will usually allow more functional range

of single binocular vision in up and downgaze. Care should be taken to not disturb Tenon’s capsule and intermuscular septum beyond the bare minimum necessary to isolate the muscle, thus minimizing the inflammatory response. Powerful muscles, such as the inferior and medial recti, should be operated with non-absorbable suture to reduce the high risk of stretched scar. Oblique dysfunction is commonly overlooked − especially intorsion due to fibrosis of the superior oblique(s). Simple, graded, hang-back recessions of the superior oblique(s) at their insertions are highly effective in relieving torsional diplopia due to SO overaction.

Prior retinal detachment (RD) repair patients may experience diplopia due to visual distortion as well as strabismus. Strabismus may result from muscle fibrosis due to surgical trauma and foreign body reaction and encapsulation of the encircling hardware. Flap tears have been observed in post-RD patients, presumably due to aggressive stripping of

Tenon’s capsule from the muscle during RD repair [7, 8]; these create a deviation away from the field of action of the torn muscle. Erosion of a rectus muscle by an encircling band which has migrated anteriorly is also seen. The eroded muscle is usually found to have reattached itself posterior to the band, but with reduced function due to its recessed position. Repair of an eroded muscle or flap tear is best performed with non-absorbable suture. Bulky exoplant material may mechanically interfere with muscle function and may need to be debulked. The superior oblique tendon is frequently caught in, or scarred to, the retinal band, altering its function, and may need to be released. Each case is evaluated individually and any repair should attempt to correct the pathology with minimal dissection. Excessive scar tissue should be addressed with the scar principles outlined previously.

Glaucoma valve procedures may cause complex strabismus due to muscle fibrosis. Usually exotropia is seen as the implants are placed in the superotemporal quadrant, causing lateral rectus fibrosis. Hypertropia is also frequent due to superior rectus fibrosis.

A large recession of the lateral rectus combined with anterior transposition of the inferior oblique through an inferotemporal fornix incision will improve exotropia and hypertropia, and reduce the risk of interfering with the bleb and valve. Bleb rupture may occur, leading to decompression of the eye. To prevent this, combined surgery with the glaucoma surgeon

allows temporary tying off of the valve stem before strabismus repair.

11.10 Helpful Hints

Torsion is under-evaluated and underappreciated in strabismus management. Torsion may be symptomatic and may also contribute to vertical misalignment. In planning the surgical approach to vertical strabismus, torsional correction may require no additional surgery other than selecting the appropriate muscle (such as recessing an inferior rectus in a hypotropic, extorted eye), or transposing a muscle as it is being recessed or resected to adjust the torsion. Advancing the tendon of the superior oblique at its insertion 3−4 mm will correct large extorsion with little vertical effect.

Balance restrictions to obtain the widest possible field of single vision. Upgaze restrictions are the easiest to deal with through the handy antielevation effect possible with the inferior oblique. When no further improvement of upgaze can be achieved in one eye, graded anterior transpositioning of the inferior oblique [15] of the other eye will often correct diplopia by creating a balanced restriction. Downgaze restrictions are more difficult to correct and sometimes it is better to convert a downgaze restriction to an upgaze restriction with an inferior rectus resection, sufficient to correct downgaze diplopia. Contralateral inferior oblique surgery can later be performed to balance upgaze. Faden sutures are also helpful to balance restrictions. A new method of Faden suture, which creates restriction through restricting muscle pulley movement, has been described [1]. This seems to be a useful approach to achieve the restrictive result without the risk of scleral perforation or excessive muscle fibrosis.

Balance incomitance in motility measurements by choosing muscles, which will produce the most effect in the field(s) of action where deviation is the greatest.

Use scar tissue to help align the eye. Scar tissue layers may be sutured directly to sclera to redirect the restrictive pull and enhance surgical outcome.

Stabilize shifted muscles in myopes with pulleytype Faden sutures [1].