Motor Fusion

Question 1

What does it mean when eyes converge?

Answer 1

They move inwards

Question 2

What does it mean when eyes diverge?

Answer 2

They move outwards

Question 3

What is motor fusion?

Answer 3

Ability to align maintain sensory fusion over a range of vergence movements

Question 4

The stronger your binocular single vision the ______ your motor fusion?

Answer 4

Higher

Question 5

How can motor fusion be measured?

Answer 5

By measuring: -Prism fusion range -20 dioptre base out (also known as the Prism Reflex Test) -Can be measure via a Synoptophere

Question 6

Why is motor fusion important?

Answer 6

Your patients prognosis is based on the presence or absense of fusion. If your patients have good motor fusion (i.e it is present) then prognosis is good. There is much hope that normal BSV can be restored thus this becomes your aim. If your patient has bad motor fusion (i.e. it is absent), there is a poor prognosis. BSV cannot be restored completely thus your aim of treatment is to ensure eyes are cosmetically acceptable.

Question 7

How do we test Motor fusion (i.e. what’s the principle)?

Answer 7

You measure fusional vergence to test motor fusion

Question 8

How may textbooks refer to also refer to fusional vergence?

Answer 8

Fusional Reserves

Fusional Amplitudes

Prism Fusion Range

Prism Vergences

Question 9

What happens to an image if you put a prism in front of an eye?

Answer 9

The image is displaced in the direction of the apex. If you only put the prism infront of one eye then the px shall experience double.

Question 10

What would happen if you put a prism in front of a px with good motor fusion?

Answer 10

They would move their eyes to avoid seeing double. With bad motor fusion this obviously wouldn’t happen.

Question 11

When you place a prism in front of a normal eye/ an eye unaffected by that prism yet which direction will the pupil move in?

Answer 11

It will move towards the direction of the apex

Question 12

How can the prism fusion test be carried out subjectively and objectively?

Answer 12

Subjectively - the px would tell you when they see double.

Objectively- you look out for eye movements i.e. that the px’s eye didn’t move in the direction of the apex thus they didn’t overcome the prism.

Question 13

Can the Prism fusion test be carried out objectively at both near and far?

Answer 13

Yes

Question 14

What does it mean if you can overcome more prism to avoid diplopia?

Answer 14

The more prism you can overcome to avoid diplopia:

The higher your amplitude/reserve motor fusion

The better your BSV (team work between eyes)

The less likely you are to decompensate

Question 15

What does it mean if you can overcome more prism to avoid diplopia?

Answer 15

The more prism you can overcome to avoid diplopia:

The higher your amplitude/reserve motor fusion

The better your BSV (team work between eyes)

The less likely you are to decompensate

Question 16

If you put base Out prism in front of your eyes what will happen?

Answer 16

They will cOnverge thus positive fusion range occurs.

Question 17

If you put base In prism in front of your eyes what will happen?

Answer 17

They will dIverge thus negative fusion range shall occur.

Question 18

What does a base up prism in front of the right eye measure?

Answer 18

Infravergence (i.e. to look down as the base is up)

Question 19

What does a base down prism in front of the right eye measure?

Answer 19

Supravergence (i.e. to look up at the base is down)

Question 20

What’s the biggest mistake students make with the Prism fusion range test?

Answer 20

They confuse it with the prism cover test.

Question 21

In the prism fusion range test why do we get the target to look at a 6/60 target rather than the line above their worst VA?

Answer 21

Because at the line above their worst VA, letters become very small thus they may miss the double vision occurring thus we like to use a big letter at 6/60.

Question 22

How do you carry out a prism fusion range test?

Answer 22

Patient sits head erect Looks at 6/60 Prism bar placed before one eye (either eye)

Strength of prism bar is increased slowly

Continue increasing strength until patient reports diplopia ALWAYS Ask them if they can make the image single again and keep going if they can Continue to increase prism

Note maximum amount of prism BEFORE diplopia is recorded - This is recorded as fusional amplitude.

Once fusion is lost decrease strength of prism until patient can regain fusion

Can carry this out at near (1/3m & 6m ) working distance and with or without glasses

Question 23

When you converge what happens?

Answer 23

You accommodate and pupils undergo miosis.

Question 24

How may accommodation affect the prism fusion range test and so what should you do?

Answer 24

—During test patient may complain of blur

—Normally when vergence changes accommodation changes by a linked amount

• Convergence increases, accommodation increases
• Divergence increases, accommodation decreases

—Note the blur point —Continue onwards until they report diplopia

Question 25

What are break point and fusional amplitude?

Answer 25

Two terms that literally describe the same thing.

Question 26

If you were strapped for time which prism fusion range test would you carry out (i.e. would it be at a distance or near , would it be with base up, base down , base in or base out prism)?

Answer 26

You would do it at whatever is most interesting e.g. if you had a right exophoric patient who presents at a distance.

You know they have no problem diverging so you would want to test their convergence thus carry out a base out prism test and do it at a distance.

Question 27

What are our normal prism fusion range values? (You need to know these off by heart)

Answer 27

The table values or higher means the px is all good.

Values lower than the table ones mean the px isn’t good.

Question 28

What is recovery in the prism fusion test?

Answer 28

The process of getting the patient to see one single image back after you have surpassed their break point.

Recovery should always be 4 dioptres less than the break point. Record this as part of the test.

Question 29

What do you have to remember when doing a vertical prism fusion range test ( i.e. your changing your base up and base down)?

Answer 29

If you carry out both a base up and base down test then you do it in front of the same eye (NEVER SWITCH EYES -because you have essentially just repeated the test).

Question 30

How can analysis of the prism fusion range test be done?

Answer 30

Compare to normal values - this one is easiest and best.

Apply Percival’s logic - Percival states that convergent and divergent fusional reserves should be balanced, one should not be less than half of the other - this ones a bit shitty though.

Apply Sheard’s logic -Sheard states opposing fusional reserve to blur point should be twice degree of phoria - requires lots of calculations cba.

Question 31

When is the 20 dioptre Base Out test used and what is it?

Answer 31

It is used:

• For Young infants
• Adults with learning difficulties
• When there’s only a Short of time in practice
• When you Don’t have a prism bar

It’s essentially a one step screening test.

Question 32

How do you carry out a 20 Dioptre base out test?

Answer 32

Single base-out prism placed before one eye & then the other (ALWAYS ON BOTH EYES)

Child fixates toy/picture at 33cm

You have to Work quickly Useful in proving presence of binocular single vision in:

• Suspected pseudostrabimus
• Child with inconclusive cover test

If a 20Δ base-out prism is not overcome encourage patient to fuse images

Important to note recovery movement as prism is removed, speed, accuracy If px does not overcome try 15 or 10 diopter prism

Question 33

What is the 4 dioptre Base Out test used to check for?

Answer 33

Not mainly used to check for motor fusion but rather for macula suppression- microtropia.

Or to clarify whether the px has central supression or macula supression.

Question 34

How is a four dioptre Base Out prism test carried out?

Answer 34

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

Both eyes make a versional movement towards apex of prism to left Left eye then converges to re-establish foveal fixation

Question 35

If you were testing for a micro-esotropia what direction prism would you use?

Answer 35

Base Out (4 dioptre prism)

Question 36

If you were testing for a micro-exotropia what direction prism would you use?

Answer 36

Base In (4 dioptre prism)

Question 37

In a prism fusion test if the eye that is covered by the prism behaves correctly but the uncovered eye doesn’t move what does the patient have?

Answer 37

Px has suppression of the uncovered eye.

Question 38

Can a synoptophore be used to investigate motor fusion?

Answer 38

Yes.