Motor Fusion Flashcards
What does it mean when eyes converge?
They move inwards
What does it mean when eyes diverge?
They move outwards
What is motor fusion?
Ability to align maintain sensory fusion over a range of vergence movements
The stronger your binocular single vision the ______ your motor fusion?
Higher
How can motor fusion be measured?
By measuring: -Prism fusion range -20 dioptre base out (also known as the Prism Reflex Test) -Can be measure via a Synoptophere
Why is motor fusion important?
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.
How do we test Motor fusion (i.e. what’s the principle)?
You measure fusional vergence to test motor fusion
How may textbooks refer to also refer to fusional vergence?
Fusional Reserves
Fusional Amplitudes
Prism Fusion Range
Prism Vergences
What happens to an image if you put a prism in front of an eye?
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.
What would happen if you put a prism in front of a px with good motor fusion?
They would move their eyes to avoid seeing double. With bad motor fusion this obviously wouldn’t happen.
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?
It will move towards the direction of the apex
How can the prism fusion test be carried out subjectively and objectively?
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.
Can the Prism fusion test be carried out objectively at both near and far?
Yes
What does it mean if you can overcome more prism to avoid diplopia?
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
What does it mean if you can overcome more prism to avoid diplopia?
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
If you put base Out prism in front of your eyes what will happen?
They will cOnverge thus positive fusion range occurs.
If you put base In prism in front of your eyes what will happen?
They will dIverge thus negative fusion range shall occur.
What does a base up prism in front of the right eye measure?
Infravergence (i.e. to look down as the base is up)
What does a base down prism in front of the right eye measure?
Supravergence (i.e. to look up at the base is down)
What’s the biggest mistake students make with the Prism fusion range test?
They confuse it with the prism cover test.
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?
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.
How do you carry out a prism fusion range test?
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
When you converge what happens?
You accommodate and pupils undergo miosis.
How may accommodation affect the prism fusion range test and so what should you do?
—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
