Lecture 14 incomitant strabismus

Question 1

What is incomitancy?

Answer 1

*The angle of deviation varies in size in different positions of gaze. Angle can get larger or smaller. Angle can change between eyes.
*The angle of deviation is greatest in the direction of limitation of eye movement.

Question 2

How can you classify incomitant strabismus?

Answer 2

congenital, acquired

1.Neurogenic: lesion with nerve supplying the muscle.

2.Myogenic: lesion directly affecting the muscle itself
3.Mechanical: lesion within the orbit that interferes with muscle action
4.Dysinnervational: resulting in developmental error in innervation of the muscle

Question 3

What types of neurogenic strabismus can you get?

What type of myogenic strabismus can you get?

What type of mechanical strabismus can you get?

What type of dysinnervational disorders can you get?

Answer 3

Neurogenic strabismus
*3rd, 4th and 6th cranial nerve palsies
*Double elevator palsy
*Double depressor palsy

Myogenic strabismus
*Myasthenia gravis
*CPEO (chronic progressive external ophthalmoplegia)

Mechanical strabismus
*Brown’s syndrome
*Thyroid eye disease
*Orbital fracture

Dysinnervational disorders
*Duanes syndrome
*Congenital fibrosis of EOM’s

Question 4

What is sherrington’s law?

What is Hering’s Law?

Answer 4

uniocular law
-agonist muscle contracts with equal and simultaneous relaxation of direct antagonist

binocular law
-equal and simultaneous contraction of contralateral synergist muscles

Question 5

What is a synergist?

What is a agonist?

What is a antagonist?

Answer 5

muscle that moves the opposite eye in the direction of agonist

primary muscle that moves eye in a given direction

muscle in the same eye that moves the eye in the opposite direction to the agonist

Question 6

What is the order of muscle sequelae?

Answer 6

1. primary muscle under action
2. over action of contralateral synergist
3. overaction of direct antagonist
4. under action of antagonist of contralateral synergist

Question 7

synergist of
SR?
IO?
MR?
SO?
IR?
LR?

Answer 7

IO
SR
LR
IR
SO
MR

Question 8

antagonist of:
IO?
SR?
LR?
IR?
SO?
MR?

Answer 8

SO
IR
MR
SO
IR
LR

Question 9

What are the reasons for CHP?

Answer 9

*Achieve single vision
*Centralise field of BSV
*Avoid area where the is diplopia/pain/discomfort
*Increase separation of diplopic images which makes them easier to ignore
*Ptosis
*Nystagmus

Question 10

How can you differentiate between a neurogenic and mechanical strabismus on ocular motility?

Answer 10

Neurogenic
*Deviation in primary position reflects the extent of the palsy
* Duction movement is greater than versions
*Saccadic movement may be slow in paretic eye
*No globe retraction
*AHP tilt common in vertical muscle palsies

Mechanical
*Often small deviation in primary position
*Duction movement = versions
*Saccadic movement the velocity is normal until point of limitation occurs
*Maybe globe retraction, pain or discomfort
*AHP tilt is rare

Question 11

What are the conditions for doing a HESS chart?

Answer 11

*Patient must have foveal fixation
*Normal retinal correspondence
*Sufficient vision in either eye to locate fixation points

Question 12

How can you differentiate between neurogenic and mechanical strabismus?

Answer 12

neurogenic
-marked deviation in PP
-diplopia remains the same
-movement greater on duction than versions
-HESS field will appear small on affected side
-no pain
-IOP is the same

mechanical
-small deviation in PP
-diplopia can reverse
-duction and version are the same
-HESS chart field will look compressed
-pain is common
-IOP rises when looking away from mechanical limitation by 5mmHg