Rare causes of mechanical strabismus, usually congenital but can present later. Aka congenital cranial dysinnervation disorders (CCDD) ## Differential diagnosis of mechanical restrictions - Trauma with muscle entrapment - Orbital mass - Duane’s - Tethering of optic nerve - Restrictive myopathies - Thyroid eye disease ## Duane syndrome - **Aberrant co-innervation of LR and MR by CNIII due to pontine dysgenesis** - Associated hypoplasia of the VI nucleus (absent on imaging) - Co-contraction of MR and LR - Sporadic/autosomal dominant (10% are familial) - F>M - Associations - Cataract - Iris anomalies - Nystagmus - Ptosis - Optic disc and foveal hypoplasia - **Marcus Gunn jaw-wink** - Microphthalmos - **Crocodile tears** (lacrimation when eating or drinking) - **Goldenhar syndrome** (oculo-auriculo-vertebral syndrome): preauricular skin tags, Duane’s, facial asymmetry/hemifacial microsomia, limbal dermoids, vertebral column anomalies, upper lid colobomas - Maternal thalidomide - Klippel-Feil syndrome (reduced cervical range of movement, short and webbed neck, low hairline) - **Wildervanck** syndrome (fusion of neck vertebrae and deafness) - Limbal dermoids: occur at the interface of the sclera and cornea - Morning Glory Syndrome - Often bilateral ### Clinical features - **Globe retraction on adduction** (due to co-contraction of MR and LR) - Reduction of the palpebral aperture on adduction - Up or downshoots on adduction: due to tight LR slipping over or under the globe - Can mimic IO overaction - Deficiency of convergence (ie. one eye fails to converge) - Systemic features: deafness, skeletal abnormalities and features of above syndromes - Ocular misalignment by subtype (**Huber classification**) - 1: **reduced abduction** and esotropia (85% of cases) - 2: **reduced adduction** and exotropia (severe globe retraction) - 3: reduced abduction **AND** adduction, orthophoria/esotropia - Face turn: to achieve BSV and avoid amblyopia (affects 10%) Duane’s syndrome tends to affect the left eye more than the right ### Treatment - Conservative: refractive, amblyopia treatment, reassurance if managing, prisms - Surgical: for BSV and head position issues (eg. bimedial recession if esotropic and bilateral recession if exotropic). Note: LR resection will worsen globe retraction. **Avoid muscle resections in Duanes**. ## Brown syndrome - Mechanical restriction due to structural/developmental abnormality of the SO tendon sheath - Produces limitation in the direction of the antagonist (IO) due to failure of SO to relax - So mimics an inferior oblique palsy but without superior oblique overaction - Causes - Congenitally short superior oblique tendon or nodule - Acquired - Trauma - Surgery (eg. RD repair) - Inflammation eg tenosynovitis in RA or scleritis - Marfan’s, Acromegaly - Improves/resolves by age 12: however congenital Brown’s rarely resolves spontaneously

Clinical features

- Limited elevation in adduction (and normal elevation in abduction) - Diplopia**if acquired** - Pain on attempting elevation in adduction - ‘Click’ (may occur during resolution) - **Minimal muscle sequelae** (overaction of contralateral synergist only) - V pattern - Downshoot in adduction (swan dive) - **Positive forced duction test**

Treatment

- Surgery if significant head posture or deteriorating binocular single vision eg. SO tenotomy. Local (retrotrochlear injection) or oral steroid for acquired cases. Compare Brown's to **inferior oblique palsy** which has (in contrast): - Significant hypotropia in primary position - Prominent muscle sequelae (ipsilateral SO overaction) - **A pattern** - Marked head posture (chin up) - Negative forced duction test ## Moebius syndrome - Rare**sporadic**congenital - Bilateral nuclear VI and VII nerve palsies: agenesis of the nerves - Associated neurological abnormalities

Clinical features

- Bilateral failure of abduction: may be a pure gaze palsy or an**esotropia** with positive forced duction testing (due to restrictive component) - Systemic features - Expressionless face - XII nerve palsies leading to atrophic tongue - Learning disability - Digital abnormalities: absent/small hand, syndactyly - Chest wall deformities: absent pectoralis muscle (Poland syndrome) ## Congenital fibrosis of the EOM (CFEOM) - Rare, non-progressive,** autosomal dominant** (CFEOM 1 chromosome 12) or autosomal recessive (CFEOM2 chromosome 11) - Distinguished from TED by the fact it is congenital - Normal muscle tissue is replaced by fibrous tissue - Bilateral ptosis and restrictive ophthalmoplegia - CFEOM1 is associated with**hypoplasia of the superior division of IIIn** leading to loss of elevation above the midline associated with a compensatory chin up posture ## Myopic strabismus fixus - Rare syndrome in high myopes with fibrous tightening of medial or lateral recti - Fixed adduction/abduction with hypotropia - MRI: deviated EOM courses and globe prolapse between the LR and SR - Surgery can be tried