10 Complex Strabismus: Restriction, Paresis, Dissociated Strabismus, and Torticollis Kenneth W. Wright his chapter on complex strabismus reviews the evaluation Tand management of incomitant strabismus associated with rectus muscle paresis and ocular restriction. Other topics include dissociated strabismus complex, torticollis, and nystag- mus. Incomitant strabismus is a deviation that changes in different fields of gaze. Incomitance can be caused by ocular restriction, extraocular muscle paresis, or oblique muscle dys- function or can be associated with a primary A- or V-pattern. The diagnosis and treatment of oblique muscle dysfunction (palsy and overaction), Brown’s syndrome, and A- and V-patterns are covered in Chapter 9. PARALYTIC RECTUS MUSCLES AND RESTRICTIVE STRABISMUS: GENERAL PRINCIPLES If an eye has limited ductions, there are only two basic causes: extraocular muscle paresis or ocular restriction. Therefore, a strabismus associated with limited ductions is secondary to extraocular muscle paresis, ocular restriction, or both. Paresis Extraocular muscle paresis means weak muscle pull, whereas palsy indicates a complete lack of muscle function. Cranial 323 324 handbook of pediatric strabismus and amblyopia nerve paresis and primary muscle disease are obvious reasons for a weak muscle that can cause limited ocular rotations. A muscle paresis can also be caused by ineffective muscle pull on the eye, or mechanical disadvantage of muscle pull. Clinical examples of conditions that cause mechanical disadvantage of muscle pull include: • A scarred or tethered muscle preventing transmission of muscle pull to the globe (e.g., floor fracture with entrapped inferior rectus muscle) • A posteriorly displaced rectus muscle (e.g., slipped muscle) • A muscle shifted out of its appropriate plane, thus dimin- ishing the vector force in the field of action of the muscle (e.g., high myopia with displaced lateral rectus muscle) Table 10-1 lists the three major causes of a mus-cle paresis: (1) cranial nerve paresis, (2) primary muscle disease, and (3) mechanical disadvantage of muscle pull. Specific types of para- lytic strabismus, including sixth and third nerve palsies, are covered later in this chapter. TABLE 10-1. Causes of Muscle Paresis. Primary muscle Mechanical disadvantage Cranial nerve palsy disease of muscle pull Third nerve palsy Botulism Stretched scar after muscle surgery Fourth nerve palsya Myasthenia gravis Slipped muscle or lost muscle (superior oblique palsy) Sixth nerve palsy CPEO Canine tooth syndrome with scarring of trochlea causing Brown’s syndrome with superior oblique palsy Trauma to muscle Miller–Fisher Floor fracture with an syndrome entrapped inferior rectus (Guillain-Barré) muscle causing limited depression Cranial nerve aberrant Agenesis of an High myopia with large innervation extraocular muscle posterior staphyloma, and syndromes (e.g., often associated slippage of lateral rectus Duane’s syndrome) with a craniofacial below globe reducing lateral disorder rectus abduction force, causing esotropia aSee Chapter 9. chapter 10: complex strabismus 325 Ocular Restriction Classically, the term ocular restriction describes a mechanical tether or leash that limits ocular rotations. Ocular restriction, however, can be caused by at least two general mechanisms: a mechanical tether on eye movements or misdirected muscle forces that work against the normal agonist muscle function. The term restriction is often loosely used as a general term for limited eye movements; however, a clear distinction should be made between ocular restriction and rectus muscle palsy. If the cause of diminished eye movements is not known, then use the term limited rotations or limitation of eye movements until the etiology is determined. Table 10-2 lists the causes of restric- tive strabismus. Mechanical restriction of eye movement is caused by adhe- sions to an extraocular muscle or sclera, a tight or inelastic extraocular muscle, or an orbital mass. Restrictive adhesions can occur from conjuctival scarring, scarring of Tenon’s capsule, orbital fat adherence, and, rarely, congenital fibrotic bands that attach to the eye or extraocular muscles. Inelastic muscle or muscle fibrosis occurs with thyroid myopathy, local anesthesia myotoxicity, and congenital muscle fibrosis (e.g., monocular elevation deficit and congenital fibrosis syndrome). An orbital mass, such as an orbital hemangioma, or a glaucoma implant can cause ocular restriction either by direct interference of rota- tion of the eye or by pressure on an extraocular muscle that tightens the muscle. Restriction resulting from misdirected muscle force vectors occurs in conjunction with aberrant inner- vation of an antagonist muscle and abnormal muscle–pulley location or a displaced extraocular muscle.20,25,83 An example of aberrant innervation causing restriction is limited adduction, often associated with Duane’s syndrome. Restricted adduction occurs because the lateral rectus muscle is aberrantly innervated by part of the medial rectus nerve. When the eye attempts to adduct, the lateral rectus muscles contracts against the con- tracting medial rectus muscle, thus restricting adduction. An example of displaced extraocular muscle is the V-pattern strabismus and superior oblique muscle underaction that are fre- quently seen in patients with craniosynostosis.20 These patients have excyclorotation of the orbits that results in superior displacement of the medial rectus muscle and limited ocular depression in adduction. The superiorly displaced medial rectus muscle pulls the eye up in addition to its normal function of 326 TABLE 10-2. Causes of Ocular Restriction. Mechanical restriction Tight extraocular muscle Structural adhesions Orbital mass Misdirected muscle forces Thyroid: Graves disease Fat adherence to muscle or sclera High myopia with large Congenital cranial nerve aberrant strabismusandamblyopia handbook ofpediatric (e.g., after strabismus surgery, posterior staphyloma innervation retinal detachment surgery, (Duane’s syndrome) or periocular trauma) Congenital fibrosis syndrome Congenital fibrotic band Orbital tumor causing Congenital ectopic extraocular muscle mass effect on globe insertion and or pulley movement (craniosynostosis, extorted orbit) Congenital Brown’s syndrome: inelastic Acquired Brown’s syndrome: Glaucoma explant with Iatrogenic displaced muscle insertion; SO muscle tendon scarring or inflammation large bleb causing antielevation after inferior oblique complex (see Chapter 9) around the trochlea mass effect on globe anteriorization with J-deformity, and movement or displace limited depression after anterior SO tendon (acquired displacement of SO tendon by Brown’s syndrome) retinal band Entrapped muscle after orbital fracture (inferior rectus most common) Fibrosis after local anesthetic injection High myopia with large posterior into a muscle (inferior most common) staphyloma and slippage of lateral rectus below globe Fat adherence to extraocular muscle (e.g., after strabismus surgery, retinal surgery, or periocular trauma) Monocular elevation deficit syndrome caused by a fibrotic inferior rectus SO, superior oblique. chapter 10: complex strabismus 327 adduction and limits depression in the field of action of the supe- rior oblique.20 A rare example of restriction caused by a displaced muscle–pulley was reported by Oh et al.83 They described a patient with limitation of elevation in adduction, or a pseudo- Brown’s syndrome, caused by a congenitally inferiorly displaced lateral rectus muscle and its pulley. These authors hypothesized that the infraplaced lateral rectus muscle and pulley act to pull the eye down, limiting elevation on adduction. Iatrogenic dis- placement of extraocular muscles during strabismus surgery can also cause limited eye movements. Inferior oblique muscle anteriorization anterior to the inferior rectus insertion can also cause active restriction and limited elevation (see Chapter 2, Fig. 2–17).15,43,114,135 In some cases, restriction and paresis coexist, such as with paretic lateral rectus muscle and secondary con- tracture of its antagonist medial rectus muscle. It is important to diagnoses the cause of limited ductions to formulate an effec- tive surgical plan. The next section describes methods for diag- nosing extraocular muscle paresis and ocular restriction. Diagnosing Restriction Versus Paresis The principal diagnostic tests that differentiate paresis from restriction include saccadic velocity measurements, forced duc- tions, and forced-generation test. Other signs influencing diag- nosis include intraocular pressure changes in various fields of gaze and lid fissure changes in sidegaze. SACCADIC VELOCITY MEASUREMENTS Saccadic velocity measurements can help differentiate restric- tion from paresis by observation, without touching the eye. Therefore, this method is useful in young children as well as adults. Saccadic movements are fast, jerk-like eye movements that require normal rectus muscle function. The rectus muscles are the major movers of the eye and are responsible for saccadic eye movements. The presence of a saccadic eye movement indi- cates normal rectus muscle function whereas the inability to stimulate a saccade suggests a rectus muscle palsy. A paretic rectus muscle does not have the power to generate a saccadic eye movement, and the eye drifts slowly to the intended field of gaze. Strabismus associated with limited ductions and diminished saccadic velocity is caused by a rectus muscle paresis, not an oblique muscle palsy. 328 handbook of pediatric