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OV2018 binocular vision > Motor Fusion > Flashcards

Motor Fusion Flashcards

1
Q

What is motor fusion ?

A

ability to maintain sensory fusion and single vision despite having over a range of vergence movements (maintenance of sensory fusion as you move your eyes around over a range of vergence movements)

Stimulus to fuse is retinal disparity (diplopia)

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2
Q

Why is motor fusion tests good ?

A

tells the strength of teamwork of both eyes

-the stronger your binocular single vision the higher the motor fusion

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3
Q

What are the 3 tests which can test motor fusion ?

A
  1. Prism Fusion Range
  2. 20 dioptre base out (Prism Reflex Test )
  3. Synoptophore
    You will not carry it out yourself
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4
Q

Why is motor fusion important ?

A

if motor fusion is present then know that px has good prognosis
-if motor fusion is absent then know that px has poorer prognosis

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5
Q

What is the good prognosis if px has motor fusion ?

A

-our treatment will be to restore them to straight eyes with BSV

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6
Q

What is the poorer prognosis if px has no motor fusion?

A

Cant restore BSV completely

-aim to look cosmetically bettwe

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7
Q

What are the different ways that motor fusion is referred to ?

A

Fusional Reserves
Fusional Amplitudes
Prism Fusion Range(PFR)
Prism Vergences

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8
Q

Why does motor fusion measure the strength of the teamwork between the 2 eyes ?

A

EXAMPLE

  • px uses fovea of both eyes to focus on an image of a tree - the px has normal straight eyes
  • Now measuring motor fusion
  • put a prism infront of right eye - base OUT PRISM
  • base OUT prism infront of one eye- move the image towards the apex
  • Px will now see 2 trees- double vision
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9
Q

what would happen if this px (from previous example) had weak motor vision ?

A

breaks down form hetrophoria into tropia

  • this px would say they see double and it would stay double
  • px is about to decompensate as they have poor motor fusion
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10
Q

What would happen If this px from the previous example had good motor vision ?

A

The px will compensate
-the px will move their eyes to compensate for diplopia
-the right eye will move in towards the nose, the cornea moves in towards nose
-cornea moves left into the nose and fovea swivels towards right
-the fovea will go back onto the 2nd image - avoiding double vision
-so by moving right eye in towards nose (into left) will stop double vision AS FOVEA MOVES
-the teamwork is better
-however due to herings law when right eye moves to left , the left eye also has to move to the left
-we will have double vision again- so not ideal
-so then the left eye will move BACK (so overcomes the prism on the other eye
) in so will be corrected
-the more prism the px can overcome the stronger the teamwork of eyes and less likely they break down into heterotropiaa.

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11
Q

What does one eye do?

A

one eye never works by itself

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12
Q

How will the left eye resolve its double vision (in previous example) ?

A

left eye finally moves into right - resolving the double vision.

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13
Q

What will happen if you put base OUT prism infront of one eye ?

A

the eyes will end up converging.

-both eyes move inwards

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14
Q

What happens if px can overcome higher and higher prism ?

A
  • the stronger the teamwork between eyes and the less they will break down into heterotrophia
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15
Q

how can we remember the apex ?

A

the apex is like an arrow that it points in the direction the eye will move
-base out- convergence

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16
Q

How can you conduct this test objectively ?

A

-where you look at their eyes and you determine when they are no longer overcoming the prism bar (e.g if put base out t- at the breaking point their eyes no longer converge and the eye diverges and moves out )

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17
Q

How can you conduct this test subjectively ?

A

when you ask the px to report when it goes into 2 and stay into 2 images

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18
Q

What else can PFR determine?

A

objectively at near

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19
Q

Why do you do the test either subjectively or oibjectively ?

A

Some patients will not report diplopia either suppress, don’t appreciate diplopia, too young so can’t talk, had a stroke

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20
Q

What happens if you can use more prism to avoid diplopia?

A
  • The higher your amplitude/reserve motor fusion
  • The better your BSV (team work between eyes)
  • The less likely you are to decompensate
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21
Q

What Is the base out prism (PFR) ?

A

-cOnvergent / pOsitive fusion range

22
Q

What its the base In prism (PFR) ?

A

dIvergent / negatIve fusion range

23
Q

What does Base Up mean (RE) ?

A

measures infravergence

-the apex is down so the eye is moving down

24
Q

What does Base Down mean (RE) ?

A
  • measures supravergence

- apex is up so the eye moves up

25
Q

How to carry out the PFR (motor fusion test)?

A
  • Patient sits head erect
  • Looks at 6/60
  • Prism bar placed before one eye (either eye)
  • Strength prism bar increased slowly
  • Continue increasing strength until patient reports diplopia
  • Then if they do see double vision - then Ask them if they can make the image single keep going if they can
  • Continue to increase prism
  • Note maximum amount of prism before diplopia is recorded - Break point

-Once fusion lost decrease strength until patient can regain fusion

  • Carry out at near (1/3m & 6m ) working distance
  • can also do at distance and with or without glasses
26
Q

What can also be asked to be reordered during the PFR test ?

A

(sometimes can be asked to write down the blur point, break point and recovery)

27
Q

What happens when px accomodates ?

A

they converge and the pupils mios

28
Q

What happens with accommodation when px doing the PFR test ?

A

the more the px converges the more accommodation they experience

  • they will converge so much that they would still see the iumage as single during the test but they will complain of blur.
  • Keep on telling px to proceed until image goes into to 2 (which is the break point)
  • However you can note down that the blur point has been reached
  • reduce strength of prism bar (recovery point)
29
Q

What is the recovery point ?

A

reduce strength of prism bar till they can see one image again

30
Q

What is the break point ?

A

when they cannot return the double image back into single

31
Q

What is the blur point ?

A

-when they accommodate too much and start to see the single image as blurry

32
Q

How do you narrow down the test for PFR ?

A

Measure the range that your most interested in first for example:

  • Exophoria Base Out
  • Esophoria BI

Then measure base-out, base-up right eye, base-in, base-down right eye

Repeat for near, distance with and without Rx if appropriate

33
Q

What happens if you are doing exercises ?

A

must measure both eyes because the risk is if you increase one you might decrease other

34
Q

What are the results for PFR that are normal ?

A

(brackets indicate the best range for young adults)

Distance Base-In
5 – 7 (10)

Distance Base-out
15 (20)

Near Base-In
15 (20)

Near Base-out
35 - 40 (40)

35
Q

What will the base out value be?

A

larger ( than base in )

36
Q

What are horizontal vergence values like?

A

-greater at near than distance

37
Q

What is the vertical prism fusion range normally at distance and near ?

A

3Δ up and down

38
Q

Check slides to memorise table

A

Distance (range D)
Near (range D)
Negative (BI)

 Blur (-8)
X
6 - 10
 Break
6 - 12
12 - 18
 Recovery (-4)
4 - 8
8 - 14
Positive (BO)
 Blur (-6)
12 - 16
20 - 28
 Break
18 - 22
26 - 34
 Recovery (-4)
14 - 18
22.30
39
Q

How to measure the vertical fusion range?

A
  • Look at 6/60 letter
  • Place prism bar base-down in front of one eye
  • Record prism power as the one just before the break point

-Repeat with either
Prism base-up in front of same eye or

-Prism base-down in front of other eye

Carry out at near (1/3m & 6m ) working distance

-use same eye -to make sure you are measuring both infravergence and supravergence

40
Q

What does Percival state ?

A

that convergent and divergent fusional reserves should be balanced, one should not be less than half of the other

41
Q

What does sheard state ?

A

states opposing fusional reserve to blur point should be twice degree of phoria

42
Q

What is the prism reflex test (20 base OUT test)?

A

Young infants
Adults with learning difficult
Short of time in practice
Don’t have a prism bar

43
Q

How to conduct the 20 D base Out test?

A
  • sit px straight
    -Child fixates toy/picture at 33cm
    -Work quickly
  • put a single base-out prism placed before one eye and look to see if eye overcomes it and then take its away to see if eye has recovered & then do for the other eye.
    -if px doesnt over come 20D do 15 or 10.
    -If a 20Δ base-out prism is not overcome encourage patient to fuse images
    -recovery movement as prism is removed, speed, accuracy
    If does not overcome try 15 or 10 diopter prism
44
Q

Why is the 20 base out test useful ?

A

Useful in proving presence of binocular single vision in:

  • Suspected pseudostrabimus
  • Child with inconclusive cover test
  • tells us if they have a reasonable level of motor fusion
45
Q

What happens to patient with suppression of right eye in the base out test ?

A
  • left eye has base out prism
  • cause left eye to move in to nose
  • herings law- right eye moved out
  • right eye - see a second image
  • RE- back of retina-their retina is suppressed because that leads to suppressed visual cortex
  • therefore then right eye moved out - can see the image fell onto supreressed retina- they couldn’t see the image
  • so they didn’t make a move back into the nose
  • now if you were to put the base out prism infront of the right eye - the right eye would not move therefore would be still suppression of right eye
46
Q

What is the 4 D base out prism test?

A

-Not mainly to check for motor fusion- to good for motor fusion
-Test for macula suppression
Suspected microtropia

  • Patient fixates letter target at distance or near
  • Fixate a tiny/letter target
  • Consider bringing prism down from above
  • Prism placed before right eye, image displaced outside macula area then left
  • Both eyes make a versional movement towards apex of prism to left
  • Left eye then converges to re-establish foveal fixation
47
Q

What are the movements of the 4 base out prism ?

A

Movements extremely small
All three movements seen with prism in front of either eye
Confirmed bifoveal fusion is present
In central suppression the affected eye will not move behind the prism
Or make a corrective fusional movement when the prism is placed over the contralateral eye

48
Q

What prism is used in suspected microesotropia ?

A

base out

49
Q

What prism is used in prism in microexotropia?

A

base in

50
Q

What does Synoptophore test?

A

Can measure
Horizontal fusional reserves
Vertical fusion reserves
Torsional reserves

51
Q

Which test would you use to measure central suppression in a px with micro exotropia?

A

4D base in test - due to small movement

  • base In prism
  • 4D base in prism
  • 4D as a small supression.

OV2018 binocular vision (15 decks)

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