lecture 3 - sensory fusion Flashcards
What is sensory fusion?
Integration of two similar images, one formed on each retina into one image within the brain, and images must be of similar brightness, size and form
How do you design a test for measuring sensory fusion?
control: both eyes being used
RE and LE are slightly different
who do you measure sensory fusion for?
Px’s with manifest strabismus
(suppression, ARC, pathological diplopia, confusion)
for the DVLA
when you investigate suppression what do you measure>
size of scotoma (area suppression)
position of scotoma
density of suppression
how do you measure area suppression/suppression scotoma
- use prisms
- place prism before the deviated eye
- increase prism until px notes double
- recorded for base in out up down
how do you measure density of suppression
sbisa and NDF bar
- put the bar of varying density of red filters
- placed in front of the fixing eye
- hold torch at 1/3 m
- px asked to view light and what colour
- increase bar strength
- px informs examiner when the light changes from red to white or diplopia or examiner has seen fixation swap
- record the density the bar above the one they report
weak suppression
if suppression is less than 10
danger of intractable diplopia
why does the light switch from red to white
px finds it difficult to use their fixing eye so the other eye Strats and the light becomes white
DVLA rules
- can’t drive
- fined £100,000
- can only drive if DVLA has confirmation that diplopia is controlled (glasses or patch) or ophthalmologist has signed it off
what is BV like in ARC
normally weaker than Normal BSV
they have abnormal BSV (ABSV)
synoptophre
test for sensory fusion
total dissociation
different targets for each eye
tests for total dissociation
synoptophre
tests for partial dissociation
single target- only part seen by one eye
Worth’s lights - red/green glasses
Bagolini Lenses - diffraction
Mallet unit- polarisation
how many lights are in worth’s lights, and what colour are they
4
2- green
1 - red
1- white
Normal BSV response with worth’s lights
1 red light (control )
2 green lights (control)
the fused white light at the bottom is a mixture of red and green (rivalry)
what size does worth’s lights come in
for use at 6m and 1/3 m viewing distance
result of worth’s lights with esotropia
uncrossed diplopia
will see 5 lights in total (3 green and 2 red)
image hits nasal retina which projects temporally
do you use red/green glasses with worth’s lights
yes
how do you manage esotropia (4 points)
- maximum plus
- base out prisms (fresnel or incorporated)
- exercises stereograms, lend prism bar
- refer to hospital eye service for surgery or second opinion
result of worth’s lights with exotropia
crossed diplopia
therefore 5 circles - 2 red and 3 green
image hits temporal retina which projects nasally
how do you manage exotropia (4 points)
- maximum minus
- base in prims (fresnel or incorporated)
- exercises stereograms, lend prism bar
- refer HES for second opinion or surgery
when using red/green glasses which eye does the red lens go in front of ?
right
result of worth’s lights with left suppression
2 red lights
result of worth’s lights with right suppression
3 green lights
how to manage constant suppression
leave it alone
Px may want cosmetic surgery
how to manage central suppression
- they may have a microtropia
- usually don’t need treatment
- BSV may be slightly worse
result of worth’s lights with ARC
normal BSV
how to manage ARC
monitor BSV (may be slightly worse than normal) do not treat
what are Bagolini Lenses also known as..
striated lenses
what do Bagolini Lenses do
they disperse light to form a street perpendicular to striations
what do the striations in Bagolini Lenses form?
partial dissociation
how do you use Bagolini Lenses?
- fixate a spot light (pen torch)
- place lenses perpendicular to each other at 45 and 135
- ask px how many lights they can see
- ask px to draw pattern they see
- ask if there are any gaps near the centre of the light
result of esotropic px using Bagolini lenses
image hits nasal retina which projects temporally
- they see 2 lights with this pattern /\
result of exotropic px using Bagolini lenses
image hits temporal retina which projects nasally
- they see 2 lights with this pattern \/
results of suppression when using Bagolini lenses
will only see 1 light and 1 lines
results of central suppression when using Bagolini Lenses
they may see gaps around the centre in one direction so you NEED to ask them about gaps
result of Bagolini Lenses with ARC
same as normal BSV
