11. Characteristics of ocular motor palsies

Question 1

What is muscle sequelae?

Answer 1

A limitation of movement in one direction of gaze can affect the innervation of other extra-ocular muscles. In long standing cases it can be difficult to ascertain which muscle is the primary underacting muscle.

Question 2

Muscle sequalae arises due to which 2 laws?

Answer 2

Herrings & Sherrington’s

Question 3

How would Hess plot look for muscle sequalae?

Answer 3

It won’t just be the underacting muscle that looks odd on the plot, but a range that looks odd.

Question 4

What is Herrings law?

Answer 4

Eye muscles responsible for each eye movement in conjugate gaze are innervated equally.

Question 5

This is an example of what law: when looking to the right the right lateral rectus and left medial rectus receive the same innervation?

Answer 5

Herrings law

Question 6

This relates to which law: when looking right, right lateral rectus contracts and the opposite right medial rectus relaxes by the same out?

Answer 6

Sherringtons law

Question 7

What does Sherringtons law state?

Answer 7

Explains how a muscle will relax when the opposite muscle contracts.

Question 8

Primary underacting muscle for the following are:
4th nerve palsy?
6th nerve palsy?
And when are this underacting muscles identified?

Answer 8

4th nerve palsy- SO
6th nerve palsy- LR

Identified when performing CT and ocular motility

Question 9

Describe the process of muscle sequelae?

Answer 9

1. Primary underacting muscle
2. Overaction of contralateral synergist (paired muscle of the other eye)
3. Overaction of ipsilateral synergist
4. Secondary inhibition of contralateral antagonist

Question 10

What is contralateral synergist?

Answer 10

Paired muscle of the other eye

Question 11

What is ipsilateral antagonist?

Answer 11

Opposite muscle in the same eye

Question 12

Muscle Sequelae is more obvious on Hess or motility?

Answer 12

Hess

Question 13

In the 2nd stage of muscle sequalae the contralateral synergist overacts, why?

Answer 13

Due to Herrings law= extra innervation is given to this muscle, but this muscle is not weak - and does not need extra innervation hence, it overacts.

Question 14

Extent of muscle sequelae depends on what 3 factors?

Answer 14

1. Duration of palsy - the longer the muscle sequelae has been present, the more concomitant the deviation will be.
2. The degree of limitation of movement- 2nd stage is greater when limitation is greater.
3. The fixing eye- if the px fixes with the affected eye, the 2nd stage will not develop to the same extent.

Question 15

Congenital and acquired nerve palsies can be controlled by?

Answer 15

1. Fusion- congenital nerve palsies have an extended fusional reserve. Obvious in vertical deviations where vertical fusional range is small.
2. AHP- used to utilize fusion completely or effiecently.
3. Both

Question 16

After recovery of nerve palsies in some cases, BSV still doesn’t return- why?

Answer 16

If a child develops nerve palsy in plastic period, then onset of diplopia initiates suppression. If suppression is present for a long time = amblyopia may develop.
If the nerve palsy recovers, suppression will not disappear and therefore BV doesn’t return.

Question 17

When are head postures used?

Answer 17

Only used when BSV is possible in a particular direction.

Question 18

In horizontal deviation, px;s turn the head in what direction?

Answer 18

Px’s turn head in direction away from underacting muscle. Face turns towards the side of underaction.
Head is turned where deviation is the least- to make fusion easy.

Question 19

Vertical deviations cause a head tilt in what direction?

Answer 19

Head tilt towards the lower eye. By tilting head to the lower eye- vertical deviation is reduced, which makes fusion for possible.

Question 20

What head movement is seen in right 4th nerve palsy?

Answer 20

SO is not working- which has the action of pulling eyes down. If weak- eyes will be relatively high then it should be - causing right hyperdeviation and left eye will be the lower eye, px will tilt head to the left.

Question 21

What head posture is seen in A and V patterns?

Answer 21

Chip up or down
Chin is moved up or down to place the eye in position with the least deviation

Question 22

Other reasons of AHP other than getting BSV? - 4

Answer 22

1. To place uniocular field in the centre
2. To avoid looking in the direction where there is pain or discomfort
3. Occasional head posture is used to increase deviation to separate diplopic images.
4. To obtain foveal fixation when movement is very restricted.

Question 23

What is seen in bilateral 3rd nerve palsy?

Answer 23

bilateral exotropia

Question 24

Is chin elevation seen in ptosis?

Answer 24

Yes, to allow binocular vision to occur