Week 2.02 Incomitant Strab Flashcards
What’s hering’s law of equal innervation
Innervation of one eye is equal to that of the other eye, resulting in movements of two eyes that are equal symmetrical and parallel
What is sherringtons law of reciprocal innervation
Contraction of each muscle is accompanied by a simultaneous and proportional relaxation of its antagonist
Stages of sequelae
1a. Underaction of the primary affected muscle
1b. Overaction of the contralateral synergistic
2. Overaction of the ipsilateral antagonist
3. Inhibitional palsy of contralateral antagonist
Which stages of the sequlae tend to occur in all incomitant deviations and which more likely to occur in neurogenic
Stages 1a and 1b tend to occur in all incomitant deviations
Stages 2 and 3 more likely to occur in neurogenic and don’t tend to occur in mechanical deviations
Abnormal head posture
- May place their eyes in position of least deviation to enable BSV
- Centralise the field of BSV
- Avoid direction of gaze where there is discomfort or pain
- Increase separation of diplopic images
What are the three ways of abnormal head posture
Face turn - left or right
Chin elevation or depression
Head tilt
Face turn
Can indicate anomaly of medial rectus and lateral rectus
Places the eyes into position of least deviation I.e. turn towards affected muscle
LLR palsy with face turn to the left
Chin elevation/depression
Place eyes in position of least deviation (e.g. in A and V syndrome)
To avoid discomfort e.g. chin is often elevated in px with dysthyroid eye disease who can find it uncomfortable to look up
Also observed in browns syndrome
Head tilt
SO palsy: Tilt away from affected side so does not have to intort
IO palsy: head tilt towards affected side
The Hess screen
WD 50cm
Dim lights
Px wears red/green goggles - red led seen by RE so only right eye will be doing fixation and with green can see green LED
Align green pen torch light with red LEDs
Red filter is the eye fixating
Green filter is the eye whose muscles your testing
If you have an over action in RIR what muscle is underacting
LSO
Interpreting Hess plots
Compare size of fields - affected eye is smaller field
Involved eye shows greatest under action and and Overaction in non involved eye
How can u tell by Hess plot if recent onset or longstanding
Asymmetrical = recent onset
Symmetrical = long standing
Down and out is a characteristic of…
3rd nerve palsy
How can you tell from a Hess plot that its a mechanical incomitancy
Plot has a very compressed appearance
Duanes retraction syndrome is mechanical
How can u tell mechanical is losing standing or recent
Mechanical deviations don’t tend to change overtime so hard to say if recent or long standing. Just need to state that its there. Not so good to use Hess plot for mechanical.
What deviations does the parks 3 step test help to investigate
Vertical incomitant deviations
What muscles will the eyes use when head tilt towards affected the right
Re - move in so incycloduction uses RSR and RSO
LE - moves out so exycloduction uses LIO and LIR
If head tilt to the left what muscles do the eyes use
RE moves out - RIR, RIO
LE moved in - LSR, LSO
What are the 3 steps in the parks 3 step technique
- Has the px got a right or left hypertropia
- Is hypertropia greater in right or left gaze
- Is hypertropia greater with a head tilt to the right or left
