differential diagnosis mechanical and neurogenical

Question 1

what are the types of neurogenic palsie

Answer 1

3rd , 4th , 6th

may be unilateral or bilateral

individual muscle palsies

Question 2

what are the type of mechanical palsies

Answer 2

Blow out

browns

duanes

adherence

cfeom

teo

retinal detachement

tumours

myositis

Question 3

what is the difference in deviation for neurogenic and mechanical deviations and ocular movements

Answer 3

deviation - size of deviation in primary position is dependent on the extent of palsy for neurogenic deviations

mechanical - In many cases despite a large restriction of movement the deviation in p.p. is very small

in neurogenic 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

in mechanical 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

Question 4

what would you find in a hess chart for neurogenic and mechanical

Answer 4

for neurogenic Field of affected eye smaller with proportional spacing between inner & outer fields. Both fields are displaced according to the deviation.

for mechanical Field of affected eye smaller with inner & outer fields being close together.

Question 5

how would interocular pressure be different in neurogenic and mechnanical

Answer 5

in neurogenic Unchanged in all gaze positions.

in mechanical Raised when looking away from the site of the lesion.

Question 6

how would force duction differ in neurogenic and mechanical

Answer 6

in neurogenic Full passive movement unless secondary muscle contracture has occurred.

in mechanical Limited passive movement generally in the opposite direction to the lesion, sometimes in the same direction or both directions.

Question 7

how does diplopia differ in in neurogenic and mechanical deviations

Answer 7

Except in IIIrd nerve & bilateral IVth the direction of diplopia remains the same e.g. R/L

in mechanical Diplopia often reverses e.g. R/L in elevation L/R in depression

Question 8

how does head posture differ in neurogenic and mechanical deviations

Answer 8

in neurogenic A combination head posture is common in neurogenic vertical muscle palsies

in mechanical Just head up / down common in mechanical restrictions

Question 9

how does pain differ in neurogenic and mechanical

Answer 9

in neurogenic No pain on movement

Pain in acquired lesions and some cases of Brown’s syndrome

Question 10

how does muscle sequelae differ in neurogenic

Answer 10

in neurogenic Full muscle sequelae esp. if longstanding
.

in mechanical o/a of contralateral synergist only

Question 11

how does saccade differ in saccades in mechanical and neurogenic

Answer 11

In neurogenic Slowed in the direction of u/a

in mechanical Normal movement comes to an abrupt end

Question 12

how does globe positon differ in neurogenic and mechanical

Answer 12

globe in neurogenic - no change in globe positon

mechanical - retraction of the globe when the eye is turned in the direction opposite to the restriction

Question 13

what is the FDT (traction test)

Answer 13

either as old procedure with local or surgery using general anesthetic

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

Question 14

what is a force duction test

Answer 14

Muscle force generation test: Four techniques have been described
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

Question 15

what is the spring back balance test

Answer 15

During surgery
Passively rotate the eye using forceps at the limbus
Remove forceps observe if eye springs back to p.p. or remains eccentric
Rotate in opposite direction, release and make similar observations
Repeat several times

Question 16

what is the muscle stretch test

Answer 16

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

Question 17

what is exaggerated force duction test

Answer 17

Used to assess tendon-laxity in superior oblique palsy

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 excyclorotated and the tests repeated.

Question 18

what electrical tests are there for muscle function

Answer 18

topical anesthetic

fine electrode inserted into the muscle

fine electrode inserted into the muscle

patient asked to look in direction of limitation and then opposite

many patients not suitable for the tests

neurogenic - partial or complete loss of motor unit activity

mechanical - increased acitivy when attempts to look in the direction of the limitation

myopthaies - may be decreased acitivy during the contraction of the affected muscle

Question 19

what is the value of differential diagnosis

Answer 19

may determine further investigations required

affects management in particular surgical correction if the deviation