Motor Functions: Fusional Reserves and Prism Tests Flashcards
What is motor fusion?
Ability to align the eyes so that sensory fusion can occur.
Motor fusion occurs with vergences.
What is stimulus?
Stimulus is retinal disparity outside Panum’s areas.
The stimuli that cause this are due to diplopia or confusion when the object of regard falls outside Panum’s area.
What is vergence?
What is version?
Vergence = eyes move in opposite directions
Version = eyes move in the same direction
What are the resting positions of vergence system?
- Distance vision requires active divergence
- Near vision requires active convergence
Therefore it is not a passive process.
For distance motor fusion:
What is the position of anatomical rest?
What is the fusion free position?
What is distance fusion?
- Anatomical rest = no nervous input to our EOMs or when eyes are closed.
- Fusion free position = no fusion but patient is awake - mostly divergent
- Distance fusion = when there is an object to look at, we get distance fusion and our visual axis becomes parallel.
For near motor fusion:
What is the fusion free position?
- Fusion free position = i.e. no stimulus to fusion. Divergent or convergent possible.
How is motor fusion at near maintained?
Motor fusion is maintain by tonus of EOMs.
What is proximal convergence?
Awareness of a near object that makes you converge.
What is accommodative convergence?
When changing from DV to NV.
Looking at a blurred image therefore need to accommodate to focus. Convergence occurs together.
Why are prisms used?
Prisms are used to assess strength of motor fusion. If prism is placed before the eyes of a person with strong binocular single vision.
It is the difference between having manifest and latent deviation.
If you have a latent deviation and:
- Good motor fusion
- Poor motor fusion
- Good fusion then you can control the deviation
- Poor fusion then that deviation is likely to become manifest.
How do you measure motor fusion?
1 - Stimulus is diplopia
[ prism placed before eye, displaces image and gives diplopia and this stimulates motor fusion ]
2 - If image falling on corresponding retinal areas is shifter
[ increase prism until the patient gets diplopia ]
3 - Upper limit possible of vergences in which diplopia can not be avoided - amplitude of accommodation
[ this is the limit of their motor fusion ]
4 - Strength of binocular single vision indicated by amount of motor fusion possible
[ the more prism that they can tolerate before they get diplopia the better their strength of their motor fusion and less likely it is for their deviation to become manifest ]
What is the amplitude of accommodation?
The upper limit possible of vergences in which diplopia can not be avoided.
What does the strength of motor fusion indicate?
It indicates the strength of binocular single vision (BSV)
How is horizontal and vertical fusion assessed?
How is cyclofusion assessed?
H and V: Using prism bars (and synoptophore)
and a fixation target. (Distance Snellen chart or Near budgie stick) [the fusion range is much less if you get the Px to view a spotlight in the distance and there is less incentive to fuse the spotlight.
Cyclofusion: Using a synoptophore [ subjective test ]
