Assessing Comitancy

Question 1

Angle of insertion for rectus muscles

Answer 1

~20 degrees with visual axis

~rectus muscles are isolated when eye is abducted 20 degrees

Question 2

Angle of insertion of oblique muscles

Answer 2

~50 degrees with visual axis

isolated when eye is adducted ~50 degrees

Question 3

What are the EOMS isolated from each position of gaze?

Answer 3

O’s to the nose

Question 4

What is the problem with attempting to isolate muscle action in a straight up or down gaze?

Answer 4

The angle of insertion is not coincident with the visual axis, elevators/ depressors are not isolated

Question 5

What type of information will straight up and down gazes provide?

Answer 5

“A” or “V” pattern

Question 6

Which law of innervation states that contralateral synergists are equally innervated?

ie RLR and LMR

Answer 6

Hering’s Law of Equal Innervation

Question 7

Which law states that the contraction of a muscle is accompanied by a simultaneous and proportional relaxation of its antagonist?

innervation/ contraction of a lateral rectus = simultaneous and proportional relaxation of the contralateral medial rectus

Answer 7

Sherrington’s Law

Question 8

3 major causes of underacting muscles?

Answer 8

1. Trauma: direct injury
2. Mechanical: faulty muscle insertion, ligament/ tendon abnormalities
3. Innervation: impairment of CN III, IV, VI

Question 9

What are the 3 causes of overacting muscles?

Answer 9

1. mechanical: faulty muscle insertion; ligament/ tendon abnormalities
2. Idiopathic
3. Hering’s Law: often due to UA muscle on fixating eye

Question 10

What are the 7 types of non-comitant deviations?

Answer 10

1. Disassociated Vertical Deviation
2. Overacting Inferior Obliques
3. A/V Patterns
4. Paresis/Paralysis (CN III, IV, VI)
5. Duane’s syndrome
6. Brown’s Syndrome
7. Strabismus Fixus

Question 11

How does the patch test differentiate congenital vs ocular torticollis?

Answer 11

patching will relieve ocular torticollis and have no effect on congenital

Ocular: abnormal head position due to diplopia

congenital: bony malformation and malformation of the sternocleidomastoid

Question 12

What is it called when a non-comitant deviation becomes more comitant?

innervation levels to the yoked muscles are reset

Answer 12

spread of comitancy

often associated with CN IV paresis

Question 13

Duction testing helps differentiate between what causes of underacting muscles?

Answer 13

innervational vs mechanical

Question 14

If duction movement is better than version, what is the likely cause of the underacting muscle?

Answer 14

Innervational cause

we can send more signal to the muscle to force the eye to go where we want it during ductions

Question 15

When ductions are >;=;< versions, the cause is mechanical

Answer 15

=

Question 16

Forced Duction testing is used to differentiate innervational from what other cause of UA?

Answer 16

mechanical

Question 17

When FDT is positive, what is present?

Answer 17

mechanical restriction

Question 18

How does spatial localized testing indicate recent onset?

Answer 18

(+) past pointing

caused by increased innervation

Question 19

When interpreting PACT, the fixating/non-fixating eye with the larger deviation is the eye with the UA muscle

Answer 19

fixating

Question 20

Which is the only test that we interpret from the patient point of view?

Answer 20

Hess Lancaster

Question 21

How do you know that a muscle is underacting when interpreting Hess Lancaster?

Answer 21

smaller enclosure = eye with UA muscle

Question 22

Park’s Three step is best at identifying paresis of which muscle?

Answer 22

superior oblique

can get any answer on an exam, but clinically suspect if answer is NOT SO

Question 23

What distance is Hess Lancaster performed at?

Answer 23

1m

Question 24

What suggests a vertical deviation, a head tilt or a head turn?

Answer 24

Head tilt

SO: tilt toward OPPOSITE shoulder (SOTO)
IO: tilt toward SAME shoulder