Neurogenic vs. Restrictive OM Flashcards
Define ‘Restrictive Eye Movements’/Mechanical?
“Caused by elements in the orbit that interfere with muscle contraction and relaxation or prevent free movement of globe”
What are some examples of Neurogenic palsies?
CNIII
CNIV
CNV
(Unilateral or Bilateral)
Individual muscle palsies
Whare some examples of Restrictive Eye Movements?
- Brown’s
- Duane’s
- Adherence syndrome
- Congenital Fibrosis of the Extraocular Muscles (CFEOM)
- Blow out
- TED
- Post retinal detachment or cataract sx
- Tumours
- Myositis
- Orbital Injuries
- Secondary Brown’s
- Post-strabismus surgery
What does Iatrogenic mean?
Caused by surgery
How does Iatrogenic Brown’s occur?
Tightened superior oblique from a SO tuck. Looking away from the leash (the tuck) it causes iatrogenic Brown’s (restricted elevation in adduction; the IO cannot elevate in adduction because the SO cannot relax)
What is a direct tether/leash?
e.g. Iatrogenic Brown’s, TED
- Tight or shortened muscle
- Limits movement when looking away from the leash
- More common
What is indirect tether/leash?
e.g. post-traumatic adhesions between conjunctiva and orbit or sinus mucocele (cystic mass). For example cyst in the lacrimal sac can cause issues in the orbit that affects the eye muscle causing a restriction.
- Limits movement when looking towards leash
- Less common
What does the deviation in pp look like in neurogenic palsies?
Size of deviation in PP is dependent on extent of the palsy
What does the deviation in pp look like in restrictive eye movements?
In many cases despite a large restriction of movement the deviation in p.p. is very small
What do OMs look like Neurogenic palsies?
Maximum limitation is in the position of the main action of the affected muscle.
The amount of movement is greater on duction than version unless a complete paralysis.
D>V
What do OMs look like in restrictive eye movements?
Restriction is usually in the opposite direction to the affected muscle & is across the field of action e.g. Blow out # restriction in elevation.
Duction & version movements are equally limited.
D=V
What is IOP like in neurogenic palsies?
Unchanged in all gaze positions.
What is IOP like in restrictive eye movements?
Raised when looking away from the site of the lesion.
Who feel pain from their eye movements? Neurogenic or Restrictive eye movements?
Neurogenic - no pain on movement
Restrictive Eye Movements - Pain in acquired lesions e.g. TED and some cases of Brown’s syndrome
What does FDT look like in neurogenic palsies?
Negative FDT
Full passive movement
unless secondary muscle contracture
has occurred e.g. in longstanding 6th
What does FDT look like in restrictive eye movements?
Positive FDT
Limited passive movement
generally in the opposite direction to the lesion, sometimes in the same direction or both directions
What are the saccades like in neurogenic palsies?
Slowed in the direction of the underaction.
What are the saccades like in restrictive eye movements?
Normal saccadic velocity until the point of the mechanical restriction, then normal movement comes to an abrupt end.
What are head postures like in neurogenic palsies?
A combination head posture is common in neurogenic vertical muscle palsies.
What are head postures like in restrictive eye movements?
Just head up / down common in mechanical restrictions.
What does the muscle sequelae look like in neurogenic palsies?
Full muscle sequelae esp. if longstanding
What does the muscle sequelae look like in restrictive eye movements?
o/a of contralateral synergist only
What does the globe look like in neurogenic palsies and in restrictive eye movements?
- No change in globe position
- Retraction of the globe when the eye is turned in the direction opposite to the restriction
What is diplopia like in neurogenic palsies?
Except in CNIII & bilateral IVth the direction of diplopia remains the same e.g. R/L
Dip may increase on one side in neurogenic but stays the same direction unless in two exceptions above
What is diplopia like in restrictive eye movements?
Diplopia often reverses e.g. L/R in elevation R/L in depression
What does a Hess Chart look like in neurogenic palsies?
Field of affected eye smaller with proportional spacing between inner & outer fields. Both fields are displaced according to the deviation.
(Except in CNIII)
What does a Hess Chart look like in Restrictive Eye Movements?
Field of affected eye smaller with inner & outer fields being close together.
“Squashed appearance”
What tests can we use for muscle function?
- Forced Duction Test
- Muscle force generation test
- Spring back balance test
- Muscle stretch test
- Exaggerated Forced Duction Test
- Electromyography
How do we conduct a Forced Duction Test (FDT)?
- Either as OPD procedure with local or during surgery under GA
- Fixation forceps, two pairs used at opposite limbal points. The globe is then rotated horizontally, vertically and obliquely. Ensure lift as well as rotate.
- Gauge the degree of limited movement and amount of resistance (requires experience)
Indenting of globe indicates tight conjunctiva - Cotton bud if forceps too uncomfortable
- Get pt to look in direction required, place bud at limbus and try to increase range of movement. Ensure don’t press down on globe
+FDT indicates a restrictive factor
How do we do a Muscle Force Generation Test? What are the 4 methods?
Method A
- The pt is instructed to look away from the field of action of muscle under investigation
- Cotton tip bud placed firmly over muscle insertion
- Pt asked to look in position of gaze of muscle action
- No or little movement of the eye = paralysis
- Pressure felt on the bud but able to prevent movement = moderate paresis
- Examiner cannot prevent eye movement = mild paresis or normal function
Method B
- Stabilise the eye with toothed forceps
- Instruct pt to move eye against this obstacle
- Determine if can feel a tug on the forceps & how much (experience required)
Method C
- As above but a moving pointer is attached to the toothed forceps
Method D
- A suction cup with a strain gauge fitted to a contact lens and applied to the eye and held by a handle
- Strain gauge registers force exerted on attempted movement
How do we do the ‘spring back balance test’?
- During surgery
- Passively rotate the eye using forceps at the limbus
- Remove forceps observe if eye springs back to pp or remains eccentric
- Rotate in opposite direction, release and make similar observations
- Repeat several times
How do we do the ‘muscle stretch test’?
- During surgery the muscle is detached and drawn forwards
- If normal it should be possible to advance its insertion to the centre of the cornea with the eye in p.p. Less than this indicates stiffness of the muscle
Why do we use the Exaggerated FDT?
Used to assess tendon-laxity in superior oblique palsy
How do we conduct the Exaggerated FDT?
The limbal conjunctiva is gripped firmly at the 4 o’clock and 10 o’clock positions for the right eye (2 o’clock and 8 o’clock positions for the left eye).
The eye is retropulsed and rotated upwards and nasally. A normal tendon will cause a mild restriction of movement which will increase with a tight tendon and decrease with a lax tendon.
The tension of the tendon can be further assessed by moving the eye back and forth in a nasal to temporal direction. In the presence of a normal tendon a ‘bump’ will be felt as the eye moves between these two positions. An absent ‘bump’ indicates significant tendon laxity and also confirms complete division of the tendon following tenotomy.
If the above manoeuvre suggests significant tendon laxity the eye should be excyclo-rotated and the tests repeated.
How do we conduct Electromyography?
- Topical anaesthesia
- Fine electrode inserted into the muscle
- Pt asked to look in direction of limitation and then opposite
- Many pts not suitable for test
What results do we get from Electromyography in neurogenic, mechanical or myopathies?
Neurogenic: partial or complete loss of motor unit activity
Mechanical: increased activity when attempts to look in direction of limitation
Myopathies: may be decreased activity during contraction of affected muscle
