lecture 4- motor fusion cont. Flashcards
if motor fusion is present, what is the prognosis?
good prognosis
- aim to restore straight eyes with BSV
if motor fusion is absence, what is the prognosis?
poor prognosis,
- can’t restore BSV completely
- aim to make cosmetically acceptable
how do you measure motor fusion
you measure fusional vergence
fusional vergence is also known as..
fusional reserves
fusional amplitudes
prism fusion range
prism vergences
how does prism fusion range measure the strength of teamwork?
normal Px uses fovea of both eyes to view the tree
- place base out prism in front and the image will be displaced towards the apex
- now the normal px will see double and move their eye towards the nose so the fovea will be looking at the tree to avoid diplopia
- when the eye moves in towards the nose, the other eye will move temporal then moves nasal to resolve it
- this is convergence as both eyes move in towards the nose
- the larger the prism they can overcome the better the motor fusion therefore the less likely they are to break down into heterophoria
PFR can be determined objectively at distance or near?
near
the better your BSV or PFR the less likely you are to….
decompensate
base out prism measures …
positive fusion range
base in prism measures…
negative fusion range
base up measures
infravergence
base down measures …
supravergence
how to carry out prism fusion range
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
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
note the blur point, break and recovery
during the PFR test the patient may complain of blur. why ?
blur point of accommodation is achieved
when accommodation increases, what happens to convergence?
increaases
when accommodation decreases, what happens to divergence?
increases
normal range for distance base IN for PFR test
5-7 prism dioptres
normal range for distance base OUT for PFR test
15 prism dioptres
normal range for near base IN for PFR test
15 prism dioptres
normal range for near base OUT for PFR test
35-40 prism dioptres
recover is usually how many prism dioptres before break
4
blur is how many prism dioptres before break
6-8
how to measure vertical fusion rnage
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
Percival’s analysis of prism fusion range…
convergent and divergent fusional reserves should be balanced, one should not be less than half of the other
according to Percival’s anaylsis of PFR, would normals be considered normal?
no
Sheard’s analysis of PFR
opposing fusional reserve to blue point should be twice the degree of phoria
insufficient fusional reserves may result in motor fusion breaking down which means Px will get…
diplopia and asthenopic symptoms
what is orthophoria
no phoria
what is the base in fusional reserve for orthophoric px
14
what is the base out fusional reserve for orthophoric px
14
who do you carry out the 20 base out test for?
young infants
adults with learning difficulties
short time in practice
don’t have a prism bar
disadvantage of the 20 base out test
doesn’t quantify the amount of prism- essentially a screening test
how to carry out the 20 base out test
Single base-out prism placed before one eye & then the other
Child fixates toy/picture at 33cm
Work quickly
If a 20Δ base-out prism is not overcome encourage patient to fuse images
Also important to note recovery movement as prism is removed, speed, accuracy
If does not overcome try 15 or 10 diopter prism
the 20 diopter test useful in proving presence of BSV in…
Suspected pseudostrabimus
Child with inconclusive cover test
what is the 4 base out test used for?
testing macula suppression (suspected microtropia)
how to carry out the 4 base out test
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
if all 3 movements are seen with the 4 base out test then the px has…
confirmed bifoveal fusion
if the px has central suppression, on the 4 base out prism test, will the affected eye move behind the prism?
no
for 4 base out test, base out is used in..
suspected microtropia
for 4 base out test, base in is used in..
micro-exotropia
what does the synoptophore measure
horizontal fusional reserves
vertical fusional reserves
torsional reserves
Which test would you use to measure central suppression?
4 dioptre
Which test would you use to measure bifoveal fixation?
4 dioptre
