Assessing Comitancy Flashcards
Angle of insertion for rectus muscles
~20 degrees with visual axis
~rectus muscles are isolated when eye is abducted 20 degrees
Angle of insertion of oblique muscles
~50 degrees with visual axis
isolated when eye is adducted ~50 degrees
What are the EOMS isolated from each position of gaze?
O’s to the nose
What is the problem with attempting to isolate muscle action in a straight up or down gaze?
The angle of insertion is not coincident with the visual axis, elevators/ depressors are not isolated
What type of information will straight up and down gazes provide?
“A” or “V” pattern
Which law of innervation states that contralateral synergists are equally innervated?
ie RLR and LMR
Hering’s Law of Equal Innervation
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
Sherrington’s Law
3 major causes of underacting muscles?
- Trauma: direct injury
- Mechanical: faulty muscle insertion, ligament/ tendon abnormalities
- Innervation: impairment of CN III, IV, VI
What are the 3 causes of overacting muscles?
- mechanical: faulty muscle insertion; ligament/ tendon abnormalities
- Idiopathic
- Hering’s Law: often due to UA muscle on fixating eye
What are the 7 types of non-comitant deviations?
- Disassociated Vertical Deviation
- Overacting Inferior Obliques
- A/V Patterns
- Paresis/Paralysis (CN III, IV, VI)
- Duane’s syndrome
- Brown’s Syndrome
- Strabismus Fixus
How does the patch test differentiate congenital vs ocular torticollis?
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
What is it called when a non-comitant deviation becomes more comitant?
innervation levels to the yoked muscles are reset
spread of comitancy
often associated with CN IV paresis
Duction testing helps differentiate between what causes of underacting muscles?
innervational vs mechanical
If duction movement is better than version, what is the likely cause of the underacting muscle?
Innervational cause
we can send more signal to the muscle to force the eye to go where we want it during ductions
When ductions are >;=;< versions, the cause is mechanical
=
Forced Duction testing is used to differentiate innervational from what other cause of UA?
mechanical
When FDT is positive, what is present?
mechanical restriction
How does spatial localized testing indicate recent onset?
(+) past pointing
caused by increased innervation
When interpreting PACT, the fixating/non-fixating eye with the larger deviation is the eye with the UA muscle
fixating
Which is the only test that we interpret from the patient point of view?
Hess Lancaster
How do you know that a muscle is underacting when interpreting Hess Lancaster?
smaller enclosure = eye with UA muscle
Park’s Three step is best at identifying paresis of which muscle?
superior oblique
can get any answer on an exam, but clinically suspect if answer is NOT SO
What distance is Hess Lancaster performed at?
1m
What suggests a vertical deviation, a head tilt or a head turn?
Head tilt
SO: tilt toward OPPOSITE shoulder (SOTO)
IO: tilt toward SAME shoulder
