In incomitant strabismus, the angle between the visual axes changes according
to the direction of gaze.
Incomitant strabismus is often grouped into neurogenic or mechanical types;
however, the abnormality may occur in the brainstem, nerve, neuromuscular
junction, muscle, or orbit.
In assessing 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.
3. Neurogenic Strabismus
Underaction with reduced saccadic velocity in the field of action of the paretic
muscle (underaction may be more marked for versions than duc tions); may
develop full sequelae with time.
• Hess chart: inner and outer fields are equally affected; full sequelae, if long standing,
• Underaction of palsied muscle.
• Overaction of contralateral synergist (yoke muscle).
• Underaction of contralateral antagonist.
• Forced duction test: full passive movement, unless chronic contracture of ipsilateral
• Further investigation and treatment: according to cause (third nerve disorders, Fourth
nerve disorders, Sixth nerve disorders(.
4. Mechanical Strabismus
Limitation in direction away from restricted muscle (equal for ductions and
versions); saccades of normal speed, but sudden early stop due to restric tion;
IOp increase in direction of limitation, often with globe retraction.
• Hess chart: inner and outer fields are compressed in direction of limitation; outer
affected more than inner; sequelae limited to overaction of contralateral synergist.
• Forced duction test: reduced passive movement in direction of limitation.
• Further investigation and treatment: according to cause (thyroid eye disease,
Orbital fractures, Duane syndrome, Congenital fibrosis of the eOM (CFeOM) ).
6. Myasthenic Strabismus
Variable and fatiguable ocular motility disturbance (any pattern), often associated
with ptosis; sustained eccentric gaze of ≥1min or repeated saccades demonstrate
fatigue; Cogan’s lid twitch (ask patient to look down for 20s and then at object in the
1° position; positive if lid ‘overshoots’); may have systemic involvement (e.g. proximal
muscle weakness, speech, breathing).
• Hess chart: range from normal to highly variable.
• Forced duction test: full passive movement.
• Ice-pack test: measure ptosis; place ice, wrapped in a towel/ glove, on the closed eyelid
for 2min; remeasure ptosis; test significantly positive if ≥2mm improvement.
• Further investigation (including serum antibodies and EMG) and treatment.
7. Myopathic Strabismus
gradual, symmetrical, non fatiguable loss of movement associated with ptosis is
seen in the inherited myopathies (e.g. CpeO group). Acquired myopathies (e.g.
teD and myositis) may be regarded as causing a mechanical strabismus pattern.
• Hess chart: symmetrical and proportional reduction in inner and outer fields.
• Further investigation and treatment: according to cause.
• Syndromic patterns of mechanical restriction
are uncommon causes of stra bismus.
• They are usually congenital, although later
presentations may occur.
1. Duane syndrom
2. Brown syndrome
3. Moebius syndrome (syn Möbius syndrome)
4. Congenital fibrosis of the EOM (CFEOM)
5. Myopic strabismus fixus
9. Duane syndrome
this is thought to arise due to aberrant coinnervation of LR and MR by IIIn, which
may be associated with VI nucleus hypoplasia.
It is usually sporadic but may be AD.
• Retraction of globe (with reduction of palpebral aperture) on attempted adduction; ±
up / downshoots on attempted adduction; additional features according to type (see
• Systemic associations (30%): deafness, goldenhar syndrome, Klippel– Feil syndrome,
Wilderwank syndrome (Duane, Klippel– Feil, and deafness).
• The types of Duane syndrome can be described according to the Huber classification
,which is based on eMg findings, or the Brown clas sification, which is based on clinical
• Assess and treat for refractive error and potential amblyopia.
•Reassure if managing well with minimal/ mild compensatory head posture; most
require no further intervention.
•Consider prisms for comfort or to improve head position.
•Consider surgery to improve BSV and head position.
•Usual practice is uni / bilateral MR recession for esotropic Duane and uni /
bilateral LR recession for exotropic Duane. Avoid LR resection, as it increases
retraction more than improving abduction.
13. Brown syndrome
This is a mechanical restriction syndrome that Brown attributed to the SO
It appears to arise from structural or developmental abnormalities of the SO
muscle/ tendon or the trochlea, leading to limitation in the direction of its
antagonist (IO) due to apparent failure of relaxation of the SO. In most cases, it
is congenital (or at least infantile) and usually improves or resolves (at least
symptomatically) by 12y of age. Acquired cases may arise due to trauma,
surgery (e.g. SO tuck, buckling, orbital), or inflammation (e.g. RA, sinusitis).
14. Clinical features
1. Limited elevation in adduction ± pain/ click (‘click’ often occurs during reso
2. limited sequelae (i.e. overaction of contralateral SR only).
3. V pattern; may downshoot in adduction (swan dive).
4. positive forced duction test.
•Reassure if managing well with minimal/ mild compensatory head posture;
usually improves with age, and upgaze is less of an issue with i patient vertical
•Consider surgery if significant abnormal head posture or if strabismus in 1°
position. the aim is to release the restriction, e.g. with SO tenotomy, until a
repeated traction test demonstrates free rotation of the globe.
• SO palsy, and results are often disappointing.
•Acquired causes may be treated with periocular or oral corticosteroids.
15. Moebius syndrome (syn Möbius
This rare sporadic congenital syndrome includes bilateral nuclear Vin and VIIn palsies and
often other neurological abnormalities.
It is included here, as it may be associated with bilateral tight MR causing restriction, in addition
to the horizontal gaze palsy.
• Bilateral failure of abduction; may be pure gaze palsy, or bilateral tight MR can lead to esotropia
and positive forced duction test.
• Systemic associations:
1. Bilateral VII palsy (expressionless face),
2. Bilateral xII palsy (atrophic tongue),
4. Digital abnormalities.
16. Congenital fibrosis of the EOM (CFEOM)
This rare congenital syndrome probably arises due to abnormal development of
the oculomotor nuclei.
Classic CFeOM (CFeOM1) is AD Chr 12q. there is bilateral restrictive
ophthalmoplegia and ptosis, with an inability to elevate the globes above the
CFeOM2 is AR Chr 11q. there is bilateral ptosis, wide angle exotropia, and severe
limitation of horizon tal and vertical movements.
In CFeOM3 Chr 16q, there are more variable motility defects and genetic
CFeOM4 (Ch21q, tukel syndrome) and CFeOM5 (COL25A1 mutation, Ch4q25).
17. Myopic strabismus fixus
This is a rare, well recognized acquired syndrome seen in high myopes.
The eye is often fixed in adduction with hypotropia.
MRI shows deviated courses of the eOMs, with globe prolapse between LR and
Surgery involves ipsilateral myopexy of LR and SR (after yokoyama) ± MR