Engle EC, Goumnerov BC, McKeown CA, et al: Oculomotor nerve and muscle abnormalities in congenital fibrosis of the extraocular muscles. Ann Neurol 41:314–325, 1997.

Engle EC, Kunkel LM, Sprecht LA, Beggs AH: Mapping a gene for congenital fibrosis of the extraocular muscles to the centromeric region of chromosome 12. Nat Genet 7:69–73, 1994.

Hertle RW, Katowitz JA, Young TL, et al: Congenital unilateral fibrosis, blepharoptosis, and enophthalmos syndrome. Ophthalmology 99:347– 355, 1992.

Traboulsi El, Jaafar M, Kattan HM, Parks MM: Congenital fibrosis of the extraocular muscles: Report of 24 cases illustrating the clinical spectrum and surgical management. Am Orthop J 43:45–53, 1993.

222 CONVERGENCE INSUFFICIENCY

378.83

Stephen P. Christiansen, MD

Minneapolis, Minnesota

ETIOLOGY/INCIDENCE

Convergence insufficiency is a common ocular motility disturbance characterized by an exophoria or intermittent exotropia that is greatest at near fixation. It is one of the most common ocular motility causes of asthenopia. Convergence insufficiency is caused by poor fusional convergence at near fixation.

COURSE/PROGNOSIS

Patients typically present in their teens or early adulthood and complain of gradually worsening eyestrain, periocular headache, blurred vision after brief periods of reading, and sometimes crossed diplopia with near work. It is not unusual for the patient to squint one eye while reading to relieve the blurring or diplopia. Few, if any, symptoms are present at distance fixation. Symptoms are aggravated by illness, fatigue, anxiety, and prolonged near work. Untreated, the exophoria at near may break down to a poorly controlled intermittent exotropia. In most cases, convergence insufficiency is very amenable to orthoptic treatment.

DIAGNOSIS

Clinical signs and symptoms

●Remote near point of convergence. Patients are unable to maintain fixation on a fusional target as it is brought up to the tip of their nose.

●Significant exophoria or intermittent exotropia at near. More rarely, patients will be orthophoric or even exhibit a small degree of esophoria at near. However, all will have a remote near point of convergence.

●Small to non-existent exophoria at distance.

●May have reduced stereo-acuity at near.

●Normal near point of accommodation.

the bifocal may be sufficient to make the patient symptomatic.

●Convergence insufficiency associated with accommodative insufficiency. Patients with combined convergence and accommodative insufficiency are usually more symptomatic than those with convergence insufficiency alone. However, symptoms alone are not sufficient to distinguish between these two entities, and all patients who present with convergence insufficiency should have accommodative amplitudes checked since satisfactory treatment will depend on a correct diagnosis. Anticholinergic drugs, closed head trauma, and viral encephalopathies should be considered in the pathogenesis of this disorder. In addition to treating the convergence weakness, plus lenses should be prescribed for reading in these patients.

●Convergence paralysis. In this condition, the patient is able to adduct the eyes, but cannot converge, and has constant diplopia at near. This is usually a result of significant closed head trauma, but can also result from a lesion in the midbrain, toxic encephalopathy, or from encephalitis. It may or may not be associated with accommodative insufficiency. Base-in Fresnel prisms in the reading add of the bifocals or ground-in prisms in a separate pair of reading glasses may be useful in restoring binocularity at near in these patients.

TREATMENT

Medical/orthoptics

●Near point of convergence exercises. An accommodative target such as the point of a pencil (hence, pencil push-ups) is placed remote to the patient’s near point of convergence and gradually brought toward the tip of the nose with the patient converging to avoid diplopia. Just before there is a break in fusion, the patient holds fixation on the target for ten seconds. The ‘push-up’ is repeated ten times, two to four times a day until he is able to hold fixation to the tip of the nose. The exercises can be tapered and then used on an as-needed basis when the patient notices a recurrence of symptoms.

●Other forms of convergence training. Base-out prism reading, and stereogram cards may also be used by the orthoptist to improve fusional convergence.

●Base-in prisms for near only. These prisms can be ground into a separate pair of reading glasses or Fresnel membrane prisms can be fitted over the reading segment of the patient’s bifocals.

Surgical

●The decision to proceed with surgery should be made with caution, and only after all orthoptic efforts have failed. Bilateral medial rectus resections are usually the most effective operation for this condition. However, the patient should be warned about the possibility of uncrossed diplopia at distance fixation after surgery. This typically resolves within one to three months post-operatively. The exophoria at near usually recurs after several years although most patients remain asymptomatic.

Surgical

●The most commonly used procedure for DVD is a superior rectus muscle recession of 5 to 16 mm from the insertion.

●Recession and anterior displacement of the inferior oblique muscle near the temporal pole of inferior rectus muscle is another common procedure for DVD. Some surgeons recommend this surgery for isolated DVD, however, most experts prefer this approach when the DVD is associated with concomitant inferior oblique muscle overaction.

Residual DVD after large superior rectus recession may benefit from a small (5 mm or less) resection of the inferior rectus muscle. Recently, nasal myectomy of the inferior oblique muscle has been advocated if the inferior oblique muscle has previously been recessed and anteriorized.

Other surgical approaches reported in the literature include posterior fixation of the superior rectus muscle with or without recession, botulinum toxin type A injection into the superior rectus muscle, weakening of both the superior rectus and inferior oblique muscles, graded resection with anteriorization of the inferior oblique and weakening of all four oblique muscles

●DHD may be treated with lateral rectus muscle recession of 3 to 8 mm on the affected side (or ipsilateral side).

REFERENCES

Brodsky MC: Dissociated vertical divergence: a righting reflex gone wrong. Arch Ophthalmol 117:1216, 1999.

Burke JP, Scott WE, Kutschke PJ: Anterior transposition of the inferior oblique muscle for dissociated vertical deviation. Ophthalmology 100:245, 1993.

Guyton DL: Dissociated vertical deviation: etiology, mechanism, and associated phenomena. Costenbader Lecture. J Aapos 4:131, 2000.

Schwartz T, Scott WE: Unilateral superior rectus recession for the treatment of dissociated vertical deviation. J Pediatr Ophthalmol Strabismus 28:219, 1991.

224 DUANE’S RETRACTION

SYNDROME 378.71

(Stilling–Turk–Duane Syndrome, or Duane’s Syndrome)

Shawn Goodman, MD

Lake Oswego, Oregon

COMPLICATIONS

Although uncommon, complications from surgery for DVD include limitation of elevation (especially with the inferior oblique muscle recession with anteriorization technique) overcorrection, abnormal torsion, changes in eyelid position, and secondary overaction of the contralateral inferior oblique muscle.

COMMENTS

●Anteriorization of the inferior oblique muscle changes the muscle action from elevation to depression. Its neurovascular bundle may tether the globe causing the anti-elevation syndrome with a larger hypertropia in the contralateral eye. Many surgeons avoid unilateral inferior oblique anteriorization in part because of this complication.

It can be difficult to determine whether surgery should be performed on one or both eyes. Limiting surgery to the worst eye is effective when the patient rarely fixates with that eye. However, should the operated eye take up fixation after unilateral surgery, a large vertical deviation will result in the opposite eye. Under these circumstances, bilateral surgery may be a better choice.

●When bilateral DVDs are very asymmetric, even if bilateral surgery is performed asymmetrically, the eye with the larger DVD may be significantly undercorrected.

DVD is a common companion of early-onset strabismus, and involves elevation, abduction and excyclotorsion. Its cause is still debated. Most dissociated deviations are latent or of small magnitude and do not require treatment. Treatment is indicated when the appearance of the ocular misalignment or the resulting visual symptoms are unacceptable to the patient. Complete elimination of the deviation is difficult, especially when there is bilateral involvement.

ETIOLOGY/INCIDENCE

Duane’s retraction syndrome (DRS) is a congenital, incomitant ocular motility disorder characterized by abnormal function of the lateral rectus muscle in the affected eye, together with retraction of the globe and narrowing of the palpebral fissure on attempted adduction. Generally, the lateral rectus does not abduct the eye, but instead contracts at the same time as the medial rectus on adduction. It is this simultaneous cocontraction of the medial and lateral rectus muscles on attempted adduction that causes the retraction of the globe and narrowing of the palpebral fissure when the eye is adducted.

In the primary position the ocular alignment is most commonly esotropic, but the syndrome can be present with no ocular deviation in the primary position and a minority of patients with DRS may be exotropic in primary position. EMG testing finds reduced electrical activity of the lateral rectus muscle on abduction and simultaneous electrical activity of the medial and lateral recti on adduction. Head turns to maintain binocularity are common. Marked upward or downward deviations of the eye in adduction may be seen.

DRS is most commonly unilateral, but can be bilateral. For unknown reasons, it affects the left eye more frequently (approximately 60% incidence), and approximately 60% of patients with DRS are female. There is occasionally familial inheritance, but most cases are sporadic.

DRS is believed to be due to maldevelopment or congenital absence of the sixth nerve nucleus, so that the lateral rectus muscle is instead abnormally innervated by branches of the third nerve. In the minority of patients with DRS and good abduction, it may be that the sixth nerve arrives in the orbit to innervate the lateral rectus only after branches of the third nerve have already done so. The maldevelopment or injury to developing structures probably occurs between the 4th and 8th weeks of embryogenesis, when the cranial nerves and extraocular muscles are forming. This timing also coincides with other defects in embryogenesis that can be associated with the occurrence of Duane syndrome in a minority of patients. The clinical result of this maldevelopment of the abducens nerve is a

spectrum of innervational abnormalities, with varying degrees of lateral rectus muscle paresis and aberrant innervation by the oculomotor nerve.

Secondary fibrosis of non-innervated portions of the lateral rectus muscle may develop, further limiting adduction, as well as contributing to the upshoots and downshoots in adduction that are frequently seen. This has been referred to as a ‘leash effect’ of the tight lateral rectus muscle. A less common explanation for upshoots and downshoots is the suggestion that oculomotor branches that innervate the superior or inferior rectus muscle are contributing innervation to the lateral rectus muscle, while the oculomotor subnucleus to the medial rectus is then also contributing to vertical rectus innervation. Thus, when the eye is adducting, a vertical rectus is stimulated to contract as well, leading to an upshoot or downshoot of the eye in adduction. This latter explanation does not account for the fact that vertical rectus recessions do not successfully treat upshoots or downshoots.

Rarely the medial rectus may have subnormally-developed innervation, resulting in non-innervated and fibrotic areas in the medial rectus muscle also. The medial rectus is frequently described at surgery as being tight or fibrotic, though this may also be a secondary change due to the lack of opposing normal lateral rectus function.

DRS is present in 1–4% of strabismus patients. There are a variety of clinical findings in patients with DRS, generally divided into 3 types. The clinical spectrum across these types results from the variability of innervation of the affected lateral rectus muscle. That is, the balance of subnormal sixth nerve innervation, abnormal third nerve innervation and fibrosis in noninnervated portions of the lateral rectus muscle determines the abnormalities in ocular movements seen.

adduction together with narrowing of the palpebral fissure on adduction.

The following classification system is commonly used:

Type I

Type I represents 70–85% of patients with DRS. It is characterized by marked to moderate limitation of abduction of the affected eye (Figure 224.3) and relatively normal adduction (Figure 224.1). There is retraction of the globe and narrowing of the palpebral fissure in adduction, due to simultaneous contraction of the medial and lateral recti (both innervated by the third cranial nerve). On attempted abduction, impulses coming from the third cranial nerve subnucleus that normally subserves the medial rectus are inhibited, and the medial rectus and lateral rectus muscles of the Duane’s eye relax. This allows the globe to move forward and the palpebral fissure to widen on attempted abduction. A generally small angle of esotropia is present in the primary position (Figure 224.2). Larger angles of esotropia are occasionally seen, and exotropia occurs in about 5% of patients with type I DRS. Upshoot or downshoot of the eye in adduction may be present.

COURSE/PROGNOSIS

Many patients with DRS are able to adopt a head turn to maintain binocularity, and do so. In esotropic Type I DRS, the head turn is usually towards the affected eye, to utilize the affected eye in adduction. In exotropic Type II DRS, the head turn is usually toward the normal side, to use the affected eye in abduction.

For the most part, the deviation is stable, but one study documented a progression of the findings in many patients with DRS during the first 6 years of life. Limitation of abduction and narrowing of the palpebral fissure were seen first, with upshoot and downshoot on adduction appearing later. Marked retraction associated with enopthalmos in the primary position has been observed to be more common in adults than in children, suggesting that this finding can also be progressive over time.

FIGURE 224.1. Type I Duane’s, left eye, in adduction. Note narrowed palpebral fissure on the left.

FIGURE 224.2. Type I Duane’s, left eye, esotropia in primary position.

225 ESOTROPIA: HIGH ACCOMMODATIVE

CONVERGENCE-TO- ACCOMMODATION RATIO 378.35

Alvina Pauline Dy Santiago, MD

Metro-Manila, Philippines

Arthur L. Rosenbaum, MD

Los Angeles, California

The ratio of accommodative convergence (AC) to accommodation (A) [AC/A] is a measure of responsiveness of convergence for each diopter of accommodation.

ETIOLOGY/INCIDENCE

A high AC/A ratio is characterized by excessive accommodative convergence for the amount of accommodation required to focus clearly at a certain distance. Depending on available fusional divergence mechanisms, the excessive accommodative convergence results in esophoria or intermittent or constant esotropia. A high AC/A ratio occurs in as many as 50% of childhood esotropes.

Differential diagnosis

Nonaccommodative convergence excess refers to a condition in which patients are orthotropic or have a small-angle esotropia at distance and in whom esotropia at near exceeds distance deviation by at least 15 prism diopters. The esodeviation at near does not respond to additional spherical plus lenses, which contrasts with patients with a true high AC/A ratio. The AC/A ratio is low or normal when measured using the gradient method. In these patients, tonic convergence is suspected to cause increased esotropia at near.

Undercorrected hyperopia in patients who did not receive adequate cycloplegia prior to determination of refractive error may present clinically with esotropia at near that exceeds distance deviation despite wearing the correction. Repeat cycloplegic refraction is warranted and may uncover more hyperopia than previously discovered. The best agent for cycloplegic refraction in patients with esotropia is atropine. Prolonged discomfort with atropine has prompted some ophthalmologists to use intermediate agents such as cyclopentolate that may not uncover full hyperopia.

TREATMENT

The goal of treatment is to achieve alignment at both distance and near, to less than 8 PD of esotropia. This allows peripheral fusion, and expansion of fusional amplitudes.

COURSE/PROGNOSIS

The risk of deterioration of esotropia after successful alignment with glasses is greater in patients with a high AC/A ratio than is the risk of esotropia associated with high hyperopia alone.

DIAGNOSIS

Clinical signs and symptoms

A high AC/A ratio may develop at any age, but it usually occurs between the ages of 1 and 7 years, when the reading demand increases. It is especially common in students. Asthenopic symptoms, which are common, include eyestrain and headache. Diplopia at near is reported occasionally. Clinically, the esodeviation at near exceeds distance deviation. A high AC/A ratio may develop in hyperopic, myopic, and emmetropic patients. Amblyopia is usually not severe, unless there is concomitant anisometropic hyperopia.

Laboratory findings

In evaluating the patient with the high AC/A, perform coveruncover testing with the full refractive error corrected. Use an accommodative target with sufficient detail to eliminate the variability of accommodation. Near measurements should be taken in primary position. Be careful not to confuse high AC/A with an increased esotropia in downgaze or the reading position that may be due to a V-pattern.

The methods of determining the AC/A ratio include the heterophoria method, the gradient method, and the fixation disparity method. The details of computations are discussed more thoroughly elsewhere. In most clinical citations, esodeviation at near that exceeds distance deviation by at least 10PD may be considered to have a high AC/A ratio. Caution should be exercised, however, in labeling patients with a high AC/A when no actual computation has been performed.

Ocular

Single-vision lens

The full cycloplegic correction must be tried if the patient is young enough to tolerate the full prescription (usually younger than 5–7 years); otherwise, the maximum tolerated manifest hyperopic refraction is prescribed initially. This plus correction is pushed higher, to as close to cycloplegic refraction as possible, to control residual esodeviation before prescribing bifocals. When moderate hyperopia is corrected, both distance and near deviations are decreased. This may reduce the near deviation to esophoria or infrequent intermittent esotropia with few or no symptoms.

In patients older than 10 years who have nonrefractive esotropia with high AC/A, monovision contact lenses may be effective in reducing near-angle esodeviation. This method compromises stereoacuity and may be accompanied by asthenopia.

If there is little or no hyperopia or if single-vision correction is unsuccessful, bifocals, miotics, or both may be required.

Bifocals

Prescribe bifocals only when evidence of fusion at distance (less than 10PD) can be demonstrated; the goal of bifocals is to create the same fusional situation at near. Ensure that the full cycloplegic refraction is worn and has remained unchanged before considering the use of bifocals in these situations. This has to be verified with repeat determination of cycloplegic refraction, preferably using atropine. Use only the amount of bifocal power that is required to control the near deviation (abolish the esotropia at near or convert it to a small esophoria). Bifocal power varies between +1.50 and +3.00 diopters. In children younger than 7 years, prescribe executive or D-type lenses with a segment height that bisects the pupil to ensure the use of the bifocals at near. In adults and older children, the bifocal height may be lowered to the level of the lower lid. Fresnel membrane (add-on) prisms may be used as bifocal trials to determine effectivity and power requirements; a few days may be required

Procianoy E, Justo DM: Results of unilateral medial rectus recession in high AC/A ratio esotropia. J Pediatr Ophthalmol Strabismus 28:212– 214, 1991.

Repka MX, Connett JE, Baker JD, Rosenbaum AL: Surgery in the prism adaptation study: accuracy and dose response. Prism Adaptation Study Research Group. J Pediatr Ophthalmol Strabismus 29:150–156, 1992.

Rosenbaum AL, Bateman JB, Bremer DL, Liu PY: Cycloplegic refraction in esotropic children. Cyclopentolate versus atropine. Ophthalmology 88:1031–1034, 1981.

Rosenbaum AL, Jampolsky A, Scott AB: Bimedial recession in high AC/A esotropia. A long-term follow-up. Arch Ophthalmol 91:251–253, 1974.

von Noorden GK, Avilla CW: Nonaccommodative convergence excess. Am J Ophthalmol 101:70–73, 1986.

226 EXTRAOCULAR MUSCLE

LACERATIONS 871.4

Krista A. Hunter, MD

Portland, Oregon

David T. Wheeler, MD

Portland, Oregon

ETIOLOGY/INCIDENCE

Lacerations of extraocular muscles or their tendons without damage to the globe, eyelid and adjacent structures are extremely rare. Laceration of rectus muscles occurs more frequently as the oblique muscles insert on the posterior sclera and enjoy greater protection. The inferior rectus and medial rectus are the most frequently injured due to the fact that when the eye is threatened, forced closure of the eyelid is accompanied by Bell’s phenomenon with upward and outward movement of the eye. This places these muscles more anteriorly and renders them more susceptible to injury. If ocular trauma involves an upper lid avulsion or penetration of the superomedial orbit, the superior oblique tendon may be lacerated. In addition to ocular trauma, there have been reports of damage to the medial rectus during endoscopic sinus surgery due to the close proximity of this muscle to the ethmoid sinus and the relatively thin medial orbital wall.

TREATMENT

Ideally, reattachment of the lacerated ends of the muscle or tendon should occur promptly after the acute injury. If repair is delayed, scarring and fibrosis can lead to increased difficulty finding and repairing the muscle. However, in selected cases repair may be attempted even if significant time has passed.

When a muscle is lacerated at or near its insertion, the muscle sheath and attachment to posterior Tenon’s capsule prevent the muscle from retracting deeply into the orbit. In this case, the free end of the muscle or tendon may be located by following the empty sheath ‘hand over hand’ into the orbit. It is helpful to recall that the normal course of rectus muscles parallels the orbital wall, rather than the sclera. Painstaking effort at identifying muscle tissue is warranted. Retropulsing the globe may occasionally bring the lacerated muscle into view.

Alternative approaches for recovering a lost muscle deeper in the orbit include an anterior orbitotomy through a fornix-based transconjunctival incision and, in the case of medial rectus or superior oblique muscles, endoscopic surgery through the ethmoid sinus. The assistance of an orbital surgeon may be particularly helpful in these scenarios.

If no muscle tissue can be found for reattachment, a transposition procedure may be indicated. Full or partial tendon transfer of the two adjacent rectus muscles, with or without posterior fixation (the ‘Foster modification’), may be done with retention of the anterior ciliary artery in the remaining rectus muscle. If significant concern exists about anterior segment ischemia, a muscle splitting or vessel-sparing muscle transfer technique may be used. If there is restriction of the antagonist, a subsequent recession or injection of botulinum toxin can be done.

COMMMENTS

In any case in which extraocular muscle laceration is suspected, a full and meticulous eye exam should be performed to determine the extent of the injury and rule out globe damage, fractures, or the presence of foreign bodies. Surgical exploration is frequently required.

DIAGNOSIS

A lacerated extraocular muscle can be difficult to diagnose but should be suspected when profound motility disturbance is found in the setting of ocular trauma. Additional causes of trauma-related motility disturbance should be considered: orbital fracture leading to muscle entrapment, damage to a cranial nerve, and mechanical restriction from edema or hemorrhage associated with the injury. Forced ductions should be performed and would generally be free in cases of laceration although significant edema or hemorrhage could cause restriction. If the examination is delayed significantly from the time of injury, fibrosis and scarring can also lead to restriction.

Imaging studies can occasionally be a helpful adjunct but definitive diagnosis may not be possible without surgical exploration.

REFERENCES

Foster RS: Vertical muscle transpositions augmented with lateral fixation. J Am Assoc Pediatric Ophthalmol Strabismus 1:20, 1997.

Helveston EM, Grossman RD: Extraocular muscle lacerations. Am J Ophthalmol 81:754–760, 1976.

McKeown CA: Anterior ciliary vessel sparing procedure. In: Rosenbaum AL, Santiago AP, eds: Clinical strabismus management: principles and surgical techniques. Philadelphia, WB Saunders, 1999:39:516– 528.

Santiago AP, Rosenbaum AL: Selected transposition procedures. In: Rosenbaum AL, Santiago AP, eds: Clinical strabismus management: principles and surgical techniques. Philadelphia, WB Saunders, 1999:36: 476–489.

Thacker NM, Velez FG, Demer JL, Rosenbaum AL: Strabismic complications following endoscopic sinus surgery: diagnosis and surgical management. J Am Assoc Pediatric Ophthalmol Strabismus 8:488–494, 2004.

227 INFERIOR RECTUS MUSCLE

PALSY 378.81

Richard A. Saunders, MD

Charleston, South Carolina

Richard L. Golub, MD

Phoenix, Arizona

Inferior rectus muscle palsy is an uncommon clinical entity that is almost always associated with abnormalities of one or more additional extraocular muscles. When presenting as an isolated condition, it is characterized by hypertropia of the involved eye in primary gaze position. The deviation is incomitant and becomes greater in the field of action of the involved inferior rectus muscle (i.e. when the globe is abducted and depressed). Adult patients are usually symptomatic and complain of vertical diplopia, especially in down gaze.

●Inadvertent inferior rectus muscle injury during inferior oblique muscle myectomy.

●Retrobulbar anesthetic agents injected directly into the inferior rectus muscle (may initially result in paresis with ipsilateral hypertropia followed by muscle contracture and a permanent hypotropia).

●Placement of traction suture.

●Scleral buckle.

●Orbital surgery, such as fat pad removal.

●Miscellaneous orbital processes potentially causing rectus muscle paresis:

●Chronic progressive external ophthalmoplegia;

●Orbital neoplasm;

●Rectus muscle myositis;

●Thyroid-related immune orbitopathy: usually causes restriction but may have paretic component or association with myasthenia gravis.

mined onset, usually diagnosed in early childhood.

●Neurogenic: oculomotor (third cranial nerve) lesions, rarely fascicular (multiple sclerosis and midbrain metastasis), nuclear or supranuclear, but may be seen in skew deviation.

●Post viral:

●Myasthenia gravis: typically will have a fluctuating course with a history of other extraocular muscle weakness; the orbicularis oculi are usually involved.

●Orbital trauma:

●Blowout fracture (typically posterior) with muscle entrapment or injury to the oculomotor nerve;

●Inferior rectus muscle laceration (penetrating object, dog bite) (Figure 227.1);

●Inadvertent orbital entry during endoscopic sinus surgery.

●Ocular surgery:

●Extraocular muscle surgery involving:

●Excessive recession of the inferior rectus muscle;

●Lost or slipped muscle;

●Muscle belly rupture in elderly patients (pulled-in-two syndrome, or ‘PITS’);

FIGURE 227.1. Traumatic rupture of left inferior rectus muscle from dog bite with absent depression of the left eye.

careful ocular motility examination. Prism and cover or Maddox rod measurements in the diagnostic gaze positions, as well as an evaluation of ocular torsion and sensory status, are essential.

Clinical signs and symptoms

●Hypertropia typically greatest in the field of action of the involved inferior rectus muscle.

●Duction limitation (not due to a restrictive process).

●Possibly a compensatory chin-down head posture with face turn toward the involved eye.

●Mild incyclotropia may be seen on sensory testing, but is rarely symptomatic.

●Bielschowsky’s head-tilt test: positive, negative, or paradoxic results.

●Forced duction testing typically negative in cases of true inferior rectus muscle palsy, although paresis and restriction can coexist.

●Active force-generation testing demonstrating decreased muscle force necessary to confirm the diagnosis.

Differential diagnosis

Other ocular pathology may present a clinical picture similar to inferior rectus palsy.

For instance, superior rectus muscle restriction (e.g. Graves disease or myositis) may cause a hypertropia with down gaze limitation. The orbital floor adherence syndrome may also present with hypertropia, most pronounced or exclusively present in down gaze. It is most often seen after orbital floor fracture and represents a pseudoparesis of the inferior rectus muscle. The reduced infraduction is caused by mechanical limitation of the muscle excursion posteriorly along the orbital floor, simulating muscle ‘weakness.’ Patients with chronic hypertropia (e.g. longstanding superior oblique muscle palsy or skew deviation) may have limited infraduction on version testing. This problem is distinguished from inferior rectus muscle palsy by the clinical context. Duction testing can differentiate an inferior rectus paresis from a contralateral superior oblique muscle over action; ductions will shows a difference in the ability to depress the involved eye when the fellow eye is covered. Saccadic velocity elicited by optokinetic testing also