2
Ocular Motility and Cranial Nerves
Strabismus
Definition
Ocular misalignment that may be horizontal or vertical; comitant (same angle of deviation in all positions of gaze) or incomitant (angle of deviation varies in different positions of gaze); latent, manifest, or intermittent.
Phoria
Latent deviation.
Tropia
Manifest deviation.
Esotropia
Inward deviation.
Exotropia
Outward deviation.
Hypertropia
Upward deviation.
Hypotropia
Downward deviation (vertical deviations usually are designated by the hypertropic eye, but if the process clearly is causing one eye to turn downward, this eye is designated hypotropic).
Etiology
Congenital or acquired local or systemic muscle, nerve, or neuromuscular abnormality; childhood forms are usually idiopathic. See below for full description of the various types of strabismus (horizontal, vertical, miscellaneous forms). See also cranial nerve palsy, chronic progressive external ophthalmoplegia (CPEO), and myasthenia gravis.
Symptoms
Asymptomatic; may have eye turn, head turn, head tilt, decreased vision, binocular diplopia (in older children and adults), headaches, asthenopia, and eye fatigue.
Signs
Normal or decreased visual acuity (amblyopia), strabismus, limitation of ocular movements, reduced stereopsis; may have other ocular pathology (i.e., corneal opacity, cataract, aphakia, retinal detachment, optic atrophy, macular scar, phthisis) causing a secondary sensory deprivation strabismus (usually esotropia in children < 6 years old, exotropia in older children and adults).
Differential Diagnosis
See above; pseudostrabismus (epicanthal fold), negative angle kappa (pseudoesotropia), positive angle kappa (pseudoexotropia), dragged macula (e.g., retinopathy of prematurity, toxocariasis).
Evaluation
• Complete eye exam with attention to visual acuity, refraction, cycloplegic refraction, pupils, motility (versions, ductions, cover and alternate cover test), measure deviation (Hirschberg, Krimsky, or prism cover tests), measure torsional component (double Maddox rod test), Parks–Bielschowsky three-step test (identifies isolated cyclovertical muscle palsy [see Fourth Cranial Nerve Palsy section]), head posture, stereopsis (Titmus stereoacuity test, Randot stereotest), suppression/anomalous retinal correspondence (Worth 4-dot, 4 prism diopter [PD] base-out prism, Maddox rod, red glass, Bagolini’s striated lens, or after-image tests), fusion (amblyoscope, Hess screen tests), forced ductions, and ophthalmoscopy.
• Orbital computed tomography (CT) or magnetic resonance imaging (MRI) in select cases.
• Lab tests: Thyroid function tests (triiodothyronine [T3], thyroxine [T4], thyrotropin [TSH]) in cases of muscle restriction, and antiacetylcholine (anti-ACh) receptor antibody titers if myasthenia gravis is suspected. Electrocardiogram in patients with chronic progressive external ophthalmoplegia (CPEO) to rule out heart block in Kearns–Sayre syndrome. Consider edrophonium chloride (Tensilon) test, ice pack test, or anti-ACh receptor antibody test to rule out myasthenia gravis.
• Neurology consultation and brain MRI if cranial nerves are involved.
• Medical consultation for dysthyroid and myasthenia patients.
Prognosis
Usually good; depends on etiology.
Horizontal Strabismus
Esotropia
Eye turns inward; most common ocular deviation (> 50%).
Infantile Esotropia
Appears by age 6 months with a large, constant angle of deviation (80% > 35 PD); often cross-fixate; normal refractive error; positive family history is common; may be associated with inferior oblique overaction (70%), dissociated vertical deviation (DVD) (70%), latent nystagmus, and persistent smooth pursuit asymmetry.
• Treat amblyopia with occlusive therapy of fixating or dominant eye before performing surgery.
• Correct any hyperopia greater than + 2.00 diopters (D).
• Muscle surgery should be performed early (6 months to 2 years): bilateral medial rectus recession or unilateral recession of medial rectus and resection of lateral rectus; additional surgery for inferior oblique overaction, dissociated vertical deviation (DVD), and overcorrection and undercorrection is necessary in a large percentage of cases.
Accommodative Esotropia
Develops between age 6 months and 6 years, usually around age 2 years, with variable angle of deviation (eyes usually straight as infant); initially intermittent when child is tired or sick. There are three types:
Refractive
Usually hyperopic (average + 4.75D), normal accommodative convergence-to-accommodation (AC / A) ratio (3 : 1PD to 5 : 1PD per diopter of accommodation), esotropia at distance (ET) similar to that at near (ET’).
Nonrefractive
High AC / A ratio; esotropia at near greater than at distance (ET’ > ET).
• Methods of calculating AC / A ratio
(2) Lens gradient method: AC / A = (WL − NL)/ D
WL, deviation with lens in front of eye; NL, deviation with no lens in front of eye; D, dioptric power of lens used.
Mixed
Not completely correctable with single-vision or bifocal glasses.
• Muscle surgery as above should be performed if residual esotropia is greater than 10PD.
Acquired Nonaccommodative Esotropia and Other Forms of Esotropia
Due to stress, sensory deprivation, divergence insufficiency (ET ≥ ET’), spasm of near reflex, consecutive (after exotropia surgery), or cranial nerve (CN) VI palsy.
• Muscle surgery can be considered either in symptomatic cases or if angle of deviation is large (Table 2-1).
• If no evident cause, MRI indicated to rule out Arnold–Chiari malformation.
Cyclical esotropia
Very rare form of nonaccommodative ET (1 : 3000); occurs between 2 and 6 years of age; child is usually orthophoric (eyes straight) but develops esotropia for 24-hour to 48-hour periods; can progress to constant esotropia.
• Correct any hyperopia greater than + 3.00D.
• Muscle surgery as above can be performed when deviation stabilizes.
Exotropia
Eye turns outward; may be intermittent (usually at age 2 years, amblyopia rare) or constant (rarely congenital, consecutive [after esotropia surgery], due to decompensated intermittent exotropia [XT] or from sensory deprivation [in children > 5 years of age]); amblyopia rare due to alternate fixation or formation of anomalous retinal correspondence.
Basic Exotropia
Exotropia at distance (XT) equal to that at near (XT’); normal AC / A ratio, normal fusional convergence.
Convergence Insufficiency
Inability to adequately converge while fixating on an object as it moves from distance to near (increased near point of convergence); exotropia at near greater than at distance (XT’ > XT); reduced fusional convergence amplitudes. Rare before 10 years of age; slight female predilection. Symptoms often begin during teen years with asthenopia, difficulty reading, blurred near vision, diplopia, and fatigue. Common in neurodegenerative disorders, such as Parkinson’s disease, and with traumatic brain injury; may rarely be associated with accommodative insufficiency and ciliary body dysfunction.
• Consider muscle surgery: bilateral medial rectus resection should be used with caution owing to the risk of disrupting alignment at distance.
• Orthoptic exercises are controversial: near-point pencil push-ups (bring pencil in slowly from distance until breakpoint reached, then repeat 10–15 times) is the most common but is minimally effective; saccadic exercises or prism convergence exercises (increase amount of base-out prism until breakpoint reached, then repeat starting with low prism power 10–15 times) are more effective.
Pseudodivergence Excess
XT > XT’ except after prolonged patching (patch test) when near deviation increases (full latent deviation); near deviation also increases with + 3.00D lens; may have high AC / A ratio.
True Divergence Excess
XT > XT’ even after patch test; may have high AC / A ratio.
• Consider base-in prism lenses to help with convergence.
• Muscle surgery if the patient manifests exotropia over 50% of the time and is older than 4 years old: bilateral lateral rectus recession; consecutive esotropia (postoperative diplopia) can be managed with prisms or miotics unless it lasts more than 8 weeks, then reoperate (Table 2-2).
A-, V-, and X-Patterns
Amount of horizontal deviation varies from upgaze to downgaze; occurs in up to 50% of strabismus.
A-pattern
Amount of horizontal deviation changes between upgaze (larger esotropia in upgaze) and downgaze (larger exotropia in downgaze); more common with exotropia; clinically significant if difference is 10PD or greater; associated with superior oblique muscle overaction; patients may have chin-up position.
• Absolutely no superior oblique tenotomies if patient is bifixator with 40 seconds of arc of stereoacuity.
V-pattern
Amount of horizontal deviation changes between upgaze (larger exotropia in upgaze) and downgaze (larger esotropia in downgaze); more common with esotropia; clinically significant if difference is 15PD or greater; associated with inferior oblique muscle overaction, increased lateral rectus muscle innervation, underaction of superior rectus muscle, Apert’s syndrome, and Crouzon’s syndrome; patients may have chin-down position.
Figure 2-5 V-pattern esotropia demonstrating reduced esotropia in upgaze.
Figure 2-6 Same patient as shown in Figure 2-5, demonstrating increased esotropia in downgaze.
X-pattern
Larger exotropia in upgaze and downgaze than in primary position; due to secondary contracture of the oblique muscles or the lateral recti, causing a tethering effect in upgaze and downgaze.
Vertical Strabismus
Brown’s Syndrome (Superior Oblique Tendon Sheath Syndrome)
Congenital or acquired anomaly of the superior oblique tendon sheath, causing an inability to elevate the affected eye especially in adduction. Elevation in abduction is normal or slightly decreased; may have hypotropia in primary gaze causing a chin-up position, positive forced duction testing that is worse on retropulsion and when moving eye up and in (differentiates from inferior rectus restriction, which is worse with proptosing eye); V-pattern (differentiates from superior oblique overaction, which is A-pattern), no superior oblique overaction, down-shoot in adduction, and widened palpebral fissures on adduction in severe cases. Ten percent bilateral, female predilection (3 : 2) affects right eye more often than left eye. Acquired forms are associated with rheumatoid arthritis, juvenile rheumatoid arthritis, sinusitis, surgery (sinus, orbital, strabismus, or retinal detachment), scleroderma, hypogammaglobulinemia, postpartum, and trauma.
• Consider injection of steroids near trochlea or oral steroids if inflammatory etiology exists.
• Muscle surgery for abnormal head position or large hypotropia in primary position: superior oblique muscle tenotomy or tenectomy or silicon band expander, with or without ipsilateral inferior oblique muscle recession.
Dissociated Strabismus Complex: Dissociated Vertical Deviation, Dissociated Horizontal Deviation, Dissociated Torsional Deviation
Updrift, horizontal, oblique, or torsional movement of nonfixating eye with occlusion or visual inattention. Often bilateral, asymmetric, and asymptomatic; does not obey Hering’s law (equal innervation to yoke muscles). Demonstrates Bielschowsky phenomenon (downdrift of occluded eye as increasing neutral density filters are placed over fixating eye), red lens phenomenon (when red lens held over either eye while fixating on light and the red image is always seen below the white image); associated with congenital esotropia (75%), latent nystagmus, inferior oblique overaction, and after esotropia surgery.
• No treatment usually required.
• Muscle surgery for abnormal head position or if deviation is large and constant or very frequent: bilateral superior rectus recession, inferior rectus resection, or inferior oblique weakening (Table 2-3).
Table 2-3
Surgical Numbers for Vertical Strabismus Surgery
| Dissociated Vertical Deviation | |
| Magnitude | Recess SR |
| Mild | 5 mm |
| Moderate | 7 mm |
| Severe | 10 mm |
| Inferior Oblique Overaction | |
| Magnitude | Recess IO |
| Mild | 10 mm |
| Moderate | 15 mm |
| Severe | Myectomy |
SR, superior rectus; IO, inferior oblique.
Monocular Elevation Deficiency (Double Elevator Palsy)
Sporadic, unilateral defect causing total inability to elevate one eye (may have good Bell’s reflex); hypotropia in primary position and increases on upgaze, ipsilateral ptosis common, may have chin-up head position to fuse; may be supranuclear, congenital, or acquired (due to cerebrovascular disease, tumor, or infection). Three types:
Type 1
Inferior rectus muscle restriction–unilateral fibrosis syndrome.
Type 2
Elevator weakness (superior rectus, inferior oblique)–true double elevator palsy.
Type 3
Combination (inferior rectus restriction and weak elevators).
Figure 2-8 Monocular elevation deficiency (double elevator palsy) demonstrating ptosis and hypotropia of the right eye.
• May require surgery to correct residual ptosis.
Miscellaneous Strabismus
Duane’s Retraction Syndrome
Congenital agenesis or hypoplasia of the abducens nerve (CN VI) with variable dysinnervation of the lateral rectus muscle; 20% bilateral, female predilection (3 : 2), affects left eye more often than right eye (3:1). Three types (type 1 more common than type 3, and type 3 more common than type 2):
Type 1
Limited abduction; esotropia in primary position.
Type 2
Limited adduction; exotropia in primary position.
Type 3
Limited abduction and adduction.
Co-contraction of medial and lateral rectus muscles causes globe retraction and narrowing of palpebral fissure; narrowing of palpebral fissure on adduction and widening on abduction in all three types; upshoots and downshoots (leash phenomenon) common; may have head turn to fuse; amblyopia rare; rarely associated with deafness and less commonly with other ocular or systemic conditions.
Figure 2-10 Duane’s retraction syndrome type 3, demonstrating limited adduction, upshoot (leash phenomenon) and narrowing of the palpebral fissure of the left eye.
Figure 2-11 Same patient as shown in Figure 2-10, demonstrating limited abduction and widening of the palpebral fissure of the left eye.
• No treatment usually required.
• Correct any refractive error.
• Treat amblyopia.
• Muscle surgery if there is significant ocular misalignment in primary position, abnormal head position, or significant upshoot or downshoot: medial rectus muscle recession in type 1 or lateral rectus muscle recession in type 2; NEVER perform lateral rectus muscle resection. Recess medial and lateral rectus muscles in type 3 with severe retraction.
Möbius Syndrome
Congenital bilateral aplasia of CN VI and VII nuclei (CN V, IX, and XII may also be affected); inability to abduct either eye past midline; associated with esotropia, epiphora, exposure keratitis, and mask-like facies; patient may have limb deformities or absence of pectoralis muscle (Poland anomaly).
• Muscle surgery for esotropia: bilateral medial rectus recession.
• Treat exposure keratopathy due to facial nerve palsy (see Chapters 3 and 5).
Restrictive Strabismus
Various disorders that cause tethering of one or more extraocular muscles; restriction of eye movement in the direction of action of the affected muscle (these processes cause incomitant strabismus); positive forced ductions. Most commonly occurs in thyroid-related ophthalmopathy (see Chapter 1), also in orbital fractures (see Chapter 1), and congenital fibrosis syndrome.
Congenital Fibrosis Syndrome
Variable muscle restriction and fibrosis. Five types:
Generalized Fibrosis (Autosomal Dominant [AD] > Autosomal Recessive [AR] > Idiopathic)
Most severe form; all muscles in both eyes affected including levator (ptosis), inferior rectus usually affected the worst.
Congenital Fibrosis of Inferior Rectus (Sporadic or Familial)
Only inferior rectus affected.
Strabismus Fixus (Sporadic)
Horizontal muscles affected in both eyes; medial rectus more often than lateral rectus causing severe esotropia.
