Incomitant strabismus

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Incomitant strabismus

• Nadia Northway

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Definition

• Deviation varies with size and or direction of
  gaze
• In truth nearly all forms of strabismus are
  incomitant to a degree but clinically there is
  usually more than 5o difference before
  incomitancy is noted.

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Aetiology

• Vascular affects all nerves equally
• Head trauma more commonly affects IVth nerve but
  may affect all
• Aneurysm most commonly affects IIIrd nerve
• Neoplasm
• Unknown
• Other

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Systemic Diseases

• Diabetes
• Thyrotoxicosis
• Hypertension
• Aneurysm
• Giant cell arteritis
• Multiple Sclerosis
• Myasthenia Gravis

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Investigation

• History and symptoms
• External Examination
• Cover test
• Motility
• Ophthalmoscopy
• Fields

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Symptoms

• Diplopia
• Abnormal head posture-chin, turn and tilt
• Acuity
• Associated symptoms
• General health
• Injury

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External Examination

• Strabismus
• Lid position
• Injury- chemosis, oedema
• Proptosis
• Pupils
• Asymmetry

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Abnormal Head Postures

• Always turn in direction of action of palsied
  muscle e.g. LMR palsy will turn to right
• Always move chin in direction of action of
  palsied muscle e.g. LSR palsy will elevate chin
• Always tilt to lower eye

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Findings on Cover Test

• Small deviation in primary position may indicate
  very recent onset lt 36 hours or mechanical
  problem
• In palsy- will be greater when fixing with the
  affected eye and usually larger size of deviation

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Ocular Motility

• Know muscle actions
• Take patients eyes into extremes of gaze
• Use objective and subjective assessment- corneal
  reflexes and CT. Do not rely on pt reporting
  diplopia since suppression or poor VA may affect
  results.
• Hess chart and diplopia chart.

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Secondary actions

• RAD SIN- recti adduct and superiors intort
• Recti muscles pull the eye in the direction of
  their name in the abducted position
• Obliques push the eye in the direction opposite
  to their name in the adducted position

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Muscles Sequelae

• Original palsy
• Overaction of the contralateral synergist
• Overaction of the ipsilateral antagonist
• Inhibitional palsy
• This applies to neurogenic palsy and after all
  stages of sequelae have occurred concomitancy is
  achieved

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Muscle actions
IO
IO
SR
SR
MR
LR
LR
IR
SO
SO
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Mechanical sequelae

• Overaction of contralateral synergist only
• Left Browns syndrome overaction of right
  superior rectus is seen

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Interpretation of Hess Plot

• Look for smallest field to identify affected eye
• Look at center circle to determine deviation in
  primary position
• Look for area with greatest deflection to
  identify affected muscles

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Bielchowsky Head Tilt Test

• Used to differentiate between SR and SO palsy
• Muscle sequelae identical
• In left SO palsy deviation will increase when
  head tilted to left due to unopposed action of
  the LIO

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BHTT
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Head tilting test
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Third Nerve Palsy

• Complete or partial
• Rare to find individual muscles affected but
  Congenital SR palsy quite common
• May also be multiple muscle involvement including
  pupil and ciliary body

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Third Nerve Anatomy
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Superior Rectus Palsy

• Hypotropia of affected eye and may be slightly
  exo
• Chin elevation
• Can be longstanding -usually have enlarged fusion
  range and some suppression

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Inferior Rectus Palsy

• Hypertropia in primary position

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Inferior Oblique Palsy

• Hypotropia in primary position with possible
  slight eso.

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Medial Rectus palsy

• Exo deviation

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Aneurysm site to cause IIIrd CN palsy
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Complete Third Nerve Palsy

• Exotropia with hypotropia, ptosis and possible
  dilation of pupil and accommodation palsy

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Aberrant Regeneration
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Sixth nerve anatomy
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Sixth Nerve Palsy

• Esotropia which is greater on distance fixation

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Fourth Nerve Anatomy
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Fourth Nerve palsy

• Hypertropia with slight eso , eye also extorted,
  greater at near

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Duanes Retraction Syndrome
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Left Duanes on Left gaze
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Duanes syndrome
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Duanes
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Duanes
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Browns Syndrome

• Small devation in primary position but hypotropia
  of affected eye on elevation in adduction

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Browns Syndrome
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Blow Out Fracture

• May be hypotrpia or hypertropia
• Infraorbital anaesthesia
• Chemosis
• Vertical diplopia
• Restricted eye movement in upgaze and downgaze

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Blowout fracture
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Blowout fracture
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Dysthyroid eye disease

• Wet phase when muscles swell -myogenic
• Dry phase when eye movement restrictions become
  mechanical in characteristics
• Muscles affected - IR MR SR rarely LR
• Proptosis or exophthalmos
• Check Fields
• Lid retraction and lid lag

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Thyroid eye disease
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Differentiation of mechanical and neurogenic palsy

• Mechanical
• Small deviation in pp
• Ductions and versions equal
• Ceasing of movement abrupt
• Pain
• Reversal of diplopia
• Upshoots and downshoots

• Neurogenic
• Large deviation in pp
• Ductions better than versions
• Gradual failure of movement
• No pain
• No upshoots and downshoots

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Differentiation of mechanical and neurogenic palsy

• Mechanical
• Muscle sequelae- only overaction of contra syn
• Hess chart -pointed field which look squashed

• Neurogenic
• Full muscle sequelae
• Smoother filed on Hess

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Differentiate Longstanding and Acquired Deviations

• Newly acquired
• Pt aware of AHP and uncomfortable
• Diplopia
• Sudden onset
• No enlarged fusion range

• Longstanding
• AHP - fixed and pt usually unaware
• No diplopia
• Enlarged fusion ranges
• Old photographs
• Gradual onset of symptoms usually
• Amblyopia
• Suppression

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Differentiate SR and SO palsy

• SO
• Eso deviation more typical
• AHP - chin depression
• V eso pattern
• Greater vertical deviation at near
• Bielchowsky ve
• Diplopia greatest on depression

• SR
• Exo deviation more typical
• AHP- chin elevation
• V exo pattern
• Greater deviation in distance
• Bielchowsky -ve
• May have history of ptosis
• Diplopia greatest on elevation

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V exo pattern
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Guidance for referral

• Sudden onset diplopia
• Incomitant deviation previously unidentified
• Uncomfortable head posture
• Patient has localisation disturbance
• Patient symptomatic
• Other signs and symptoms