Ординатура / Офтальмология / Английские материалы / Oxford American Handbook of Ophthalmology_Tsai, Denniston, Murray_2011

586 CHAPTER 17 Strabismus

Comitant strabismus: exotropia

Exotropia is a manifest outward deviation of the visual axes relative to each other. It may be primary, secondary (associated with poor vision), or consecutive (may follow an esotropia with time or after surgical correction).

Primary exotropias may be constant or intermittent. Intermittent exotropias range according to ease of dissociation. Exotropias that are difficult to dissociate may be regarded as being at the exophoria end of the spectrum.

As with all strabismus, the assessment should include refraction, full ophthalmic examination, and addressing of amblyopic risk. It is essential to detect and rule out underlying pathology (e.g., intraocular tumor, cataract) at the outset.

Constant exotropia

Infantile (or congenital) exotropia

•Constant large-angle exotropia presenting at 2–6 months of age; often associated with ocular/CNS abnormalities. Rarely, exotropia is present at birth (congenital exotropia).

Treatment is usually surgical (e.g., bilateral LR recessions ± MR resection).

Basic constant exotropia

•Constant exotropia with same angle for near and distance, presenting after 6 months of age.

Treatment is usually surgical.

Intermittent exotropia

This is the most common form of exotropia, and usually presents at 2–5 years of age.

Basic

• Exotropia is the same for distance and near.

True divergence excess

• Exotropia is worse for distance, with normal AC:A ratio; it is rare.

Simulated divergence excess

•Exotropia is worse for distance since an iAC:A ratio (and fusional reserves) fully or partially corrects for near. This is much more

common than true divergence excess.

Treatment

Correct any myopia, astigmatism >0.75D, and high hypermetropia; treat amblyopia; use orthoptic exercises. Consider prisms, minus lenses, botulinum toxin, or surgery for more severe cases. Surgery is generally performed before 5 years of age.

Traditionally, bilateral LR recession was used when the angle was worst at distance, and unilateral LR recession /MR resection if equal or worst at near.

588 CHAPTER 17 Strabismus

Incomitant strabismus

In incomitant strabismus, the angle of deviation of the visual axes changes according to the direction of gaze. Incomitant strabismus is often grouped into neurogenic or mechanical types. In neurogenic strabismus, the abnormality may occur in the nucleus, nerve, neuromuscular junction, muscle, or orbit.

In incomitant strabismus, the aims are to identify the pattern and cause of the strabismus and address any actual or potential complications, such as amblyopia, diplopia, or poor cosmesis.

Neurogenic strabismus

There is underaction with slowing of saccades in the direction of paretic muscle (underaction may be more marked for versions than ductions). It may develop full sequelae with time (see Table 17.10).

Investigations

•Hess/Lancaster charts: inner and outer fields are differently affected, as strabismus tends to be incomitant if neurogenic. Full sequelae may develop if longstanding.

•Forced duction test: full passive movement, unless chronic contracture of antagonist

•Further investigation and treatment are according to cause (third nerve palsy, p. 547; fourth nerve palsy, p. 550; sixth nerve palsy, p. 552).

Mechanical strabismus

There is underaction in the direction away from restricted muscle (equal for ductions and versions). Saccades are of normal speed, but with sudden early stop due to restriction. Globe retraction and IOP increase in the direction of limitation (see Table 17.10).

Investigations

•Hess/Lancaster charts: inner and outer fields are compressed in the direction of limitation; outer is affected more than inner. Sequelae are limited to overaction of contralateral synergist.

•Forced duction test: reduced passive movement is in the direction of limitation. Further investigation and treatment are according to cause (thyroid eye disease, p. 475; orbital fracture, p. 87; Duane’s and other restrictive syndromes, p. 590).

Myasthenic strabismus

Variable and fatiguable ocular motility disturbance (any pattern) is often associated with ptosis. Sustained eccentric gaze of ≥1 min or repeated saccades demonstrate fatigue. Cogan’s twitch can occur (ask patient to look down for 20 sec and then at an object in the primary position: the test is positive if the lid overshoots).

Patients may have systemic involvement (e.g., speech, breathing).

590 CHAPTER 17 Strabismus

Restriction syndromes

Syndromic patterns of mechanical restriction are uncommon causes of strabismus. They are usually congenital, although later presentations may occur.

Duane syndrome

This is thought to arise from aberrant co-innervation of LR and MR by CN III, which may be associated with CN VI nucleus hypoplasia (can be seen on MRI; imaging is not necessary for diagnosis). It is usually sporadic but may be autosomal dominant.

The most common form (type I) preferentially affects girls (60%) and the left eye (60%). It is bilateral (usually asymmetric) in at least 20%.

Clinical features

•Retraction of globe (with reduction in palpebral aperture) on attempted adduction; ±upor down-shoots or attempted adduction; additional features according to classification type (Tables 17.11a, 17.11b).

•Systemic associations (30%): deafness, Goldenhar’s syndrome, Klippel–Feil syndrome, Wildervanck syndrome (Duane, Klippel–Feil, and deafness).

Table 17.11a Brown’s classification of Duane syndrome

Type Feature

AdAbduction (less dadduction)

BdAbduction (normal adduction)

*Gives rise to divergent deviation and a head posture in which the face is turned away from the side of the affected eye.

Table 17.11b Huber’s classification of Duane syndrome (based on EMG)

RESTRICTION SYNDROMES 591

Treatment

Assess and treat for refractive error and potential amblyopia. Reassure the patient if he/she is managing well with minimal or mild compensatory head posture. Consider prisms for comfort or to improve head position.

Consider surgery to improve BSV and improve head position. Usual practice is unior bilateral MR recession for esotropic Duane syndrome and unior bilateral LR recession (±MR resection) for exotropic Duane syndrome. Avoid LR resection as it increases retraction more than improving abduction.

Brown syndrome

This is a mechanical restriction syndrome, which Brown attributed to the superior oblique tendon sheath. It appears to arise from structural or developmental abnormalities of the SO trochlear–tendon complex, leading to limitation in the direction of its antagonist (IO). This results in limited or absent elevation in adduction.

In most cases, it is congenital (or at least infantile) and usually improves or resolves by 12 years of age. Acquired cases may result from trauma, surgery (e.g., SO tuck, scleral buckling, orbital), or rarely inflammation (e.g., juvenile idiopathic arthritis [JIA], sinusitis).

Clinical features

•Limited elevation in adduction ±pain/click (click often occurs during resolution); limited sequelae (i.e., overaction of contralateral SR only); V pattern; may down-shoot in adduction; positive forced duction test.

Treatment

Reassure patient if managing well with minimal or mild compensatory head posture: it usually improves with age and upgaze is less of an issue with increased height. Consider surgery if there is significantly abnormal head posture or if strabismus is in the primary position. The aim is to release the restriction until a repeated traction test demonstrates free rotation of the globe.

Complications of SO tenotomy include SO palsy, and results are often disappointing. The preferred surgical procedure is graded SO weakening using a silicone spacer or suture, which avoids this complication.

Möbius syndrome

This rare sporadic congenital syndrome includes bilateral CN VI and CN VII nerves palsies and often other neurological abnormalities. It is included here because it may be associated with bilateral tight MR, causing restriction in addition to the horizontal gaze palsy.

Clinical features

•Bilateral failure of abduction; may be pure gaze palsy, or bilateral tight MR can lead to esotropia and positive forced duction test.

•Systemic associations: bilateral CN VII palsy (expressionless face), bilateral CN XII palsy (atrophic tongue), dIQ, digital abnormalities.

592 CHAPTER 17 Strabismus

Congenital fibrosis of the extraocular muscles (CFEOM)

This rare congenital syndrome probably arises from abnormal development of the oculomotor nuclei. Classic CFEOM (CFEOM1) is autosomal dominant (Ch12).

There is bilateral restrictive ophthalmoplegia and ptosis, with an inability to elevate the globes above midline. CFEOM2 is autosomal recessive (Ch11). There is bilateral ptosis, large-angle exotropia, and severe limitation of horizontal and vertical movements. In CFEOM3 (Ch16), there are more variable motility defects.

Strabismus fixus

In this very rare sporadic congenital syndrome, the eyes are firmly fixed in adduction or occasionally in abduction. The eyes appear to be anchored both by fibrosis of the rectus muscles and additional fibrous cords. It may be associated with pathological myopia.

ALPHABET PATTERNS 593

Alphabet patterns

Horizontal deviations may vary in size according to vertical position. The deviation is measured at 30* upgaze, primary position, and 30* downgaze while fixing on a distance target. Significant incomitance is described according to the following alphabet patterns.

V pattern

Clinically significant V-pattern is defined as a horizontal deviation, which is 15 more divergent (or less convergent) in upgaze than in downgaze.

Clinical features

•V-pattern esotropia usually arises from IO overaction or SO palsy (Table 17.12). It is also associated with antimongoloid palpebral fissures (seen in patients with, e.g., Crouzon or Apert syndrome; altering the rectus insertions). Patients often adopt a chin-down posture.

•V-pattern exotropia usually arises from IO overaction. Patients adopt a chin-up posture.

Treatment

Surgical treatment for significant V patterns may require IO weakening (if overacting), vertical transposition of the horizontal rectus (upward for LR, downward for MR), and correction of the horizontal component (e.g., MR recession for esotropia; LR recession for exotropia).

For both A and V patterns, the acronym MALE identifies the direction of vertical translation: MR to Apex, LR to Ends.

A pattern

Clinically significant A-pattern is defined as a horizontal deviation, which is 10 less divergent (or more convergent) in upgaze than in downgaze.

Clinical features

•A-pattern esotropia usually arises from SO overaction (Table 17.12). It may also be associated with mongoloid palpebral fissures. Patients often adopt a chin-up posture.

•A-pattern exotropia usually arises from SO overaction. Patients adopt a chin-down posture.

Treatment

Surgical treatment for significant A-patterns may require cautious SO weakening (if overacting), e.g., SO silicone spacer, vertical translations of the horizontal rectus muscles (upward for MR, downward for LR), and correction of the horizontal component (e.g., MR recession for esotropia; LR recession for exotropia).