Sensory fusion Flashcards
What is simultaneous perception
ability to use both eyes at same time
Name the two forms of fusion
sensory fusion
motor fusion
what is stereopsis
the use of BSV to see in 3D
which worth’s 3 grades is needed to achieve the best BV/binocular function
- simultaneous perception
- Fusion (sensory & motor)
- steriopsis
what is sensory fusion
integration of two similar images, one formed on each retina into one image within the brain
images must be similar in brightness, size and form
when do you assess sensory fusion
in patients with a strabismus e.g. a tropia
what type of patient do we assess sensory fusion on
- confusion
- pathological diplopia
- suppression
- abnormal retinal correspondence
why must we know which condition a patient has before we assess their sensory fusion
because management for each condition is different
in what circumstance will you assess a patients sensory fusion without checking the type of condition
those with hetereophoria to confirm they have normal BSV
after what age does a patient get confusion and double vision
after 8 years old
name and explain the two types of confusion
- esotropia (SOT)
cyclopean eye sees superimposed e.g. tree and house
is uncommon e.g. right esotropia means nasal retina looks at tree and house and tree over laps - exotropia (XOT)
cyclopean eye sees superimposed tree and house
is uncommon
after what age does pathological diplopia occur
8 years old
name and explain the two types of pathological diplopia
- esotropia (SOT)
strabismic eye - fixation object imaged on nasal retina which is projected temporally causes uncrossed diplopia, is more common than confusion - exotropia (XOT)
strabismic eye - fixation object imaged on temporal retina which is projected nasally causes crossed diplopia, is more common than confusion
at what age can someone get pathological suppression
begins under age of 8
what is constant suppression
one blind eye
constant manifest strabismus
complete suppression of non dominant/non fixating eye
can have right eye or left eye or alternating suppression
e.g. if the right eye has esotropia the nasal retina projects temporally and px should get double vision but suppression switches the 2nd image off in the brain so px can only see one image
what is partial suppression
suppression in only a part of the image in one eye e.g. macula suppression with peripheral BSV e.g. small part of image is suppressed
what is intermittent suppression
suppression in some circumstances only e.g. in the distance and normal BSV or double vision at intermediate
how do you investigate suppression
- diagnose the presence of suppression
- measure the size and position of the scooter (important for surgery)
it can be central suppression with peripheral fusion
can measure size of scooter with prisms - measure the density of suppression which can vary
what do you measure the size and position of a scotoma with
prisms
what do you measure the density of suppression with
sbisa bar - red filter
or
NDF bar
what is area suppression also termed as
suppression scotoma
how do you use prisms to measure suppression scotoma
prism is placed before the deviated eye
prism increased until patient notes diplopia (which is out of the area of suppression)
record for base out, base in, base up and base down
how do you measure the density of suppression with a sbisa bar
- graded bar of varying density of red filters
- placed infront of the fixating eye
- px requested to view light and asked what colour which will be red as viewed by fixing eye
- filters slowly increased in strength/darkness until px cannot see through the filter
three outcomes shows the density of suppression: - patient informs examiner when the light changes from red to white as they have to use their suppressed eye in order to see
- or examiner will see fixation swap between eyes
- or px reports diplopia
- record the density
- less than 10 = suppression weak
- danger of intractable diplopia if do this test
what is the risk of measuring the density of suppression
danger of intractable diplopia
what is intractable diplopia
taking suppression away from the px which will then experience diplopia
when does abnormal (anomalies) retinal correspondence begin
in children under 8 years old
what happens in abnormal retinal correspondence
fovea of one eye learns to correspond to a non-foveal area in the other eye (pseudo fovea) and then all the retinal correspondence in the periphery also shifts
what do patients with ARC have
abnormal BSV (ABSV) for some targets but generally BSV slightly weaker than normal
what can a test for sensory fusion be achieved by
total dissociation or partial dissociation
what is total dissociation
different targets/images to each eye
each eye has a different viewing tube
what is partial dissociation
a single target/same image is seen by both eyes but each eye sees a different part of the image e.g. a part is seen by the right eye only and not the left
name three types of partial dissociation tests
- worth’s lights - red/green
- bagolini lenses - diffraction
- mallett unit - polarisation
describe the worth’s lights 4 dot test
- four lights, usually round but can be different shapes
2 green
1 red
1 white - view through red and green goggles
red filter before R eye
green filter before L eye
green is not transmitted through a red filter
red is not transmitted through a green filter
white is transmitted equally through both filters
both eyes see white light, appears red through red filter and appears green through green filter
what is the normal BSV response for the worth’s lights 4 dot test
1 red light (control)
2 green lights (control)
the fused white light appears to be a mixture of red and green/alternates but stays a single image
what sizes is the worth’s lights 4 dot test available in
use at 6M, 1M and 1/3rdM viewing distances
how can you manage esotropia
- maximum plus/minimum minus as plus relaxes accommodation so good for moving eye out
- base out prisms (fresnel or incorporated)
- exercises stereograms, lens prism bar
- refer HES - surgery or second opinion
how can you manage exotropia
- maximum minus/minimum plus stimulates accommodation for both eyes so good for bringing eye in
- base in prism (fresnel or incorporated)
- exercises stereograms, lens prism bar
- refer HES - surgery or second opinion
how do you manage constant suppression
- leave alone as no symptoms (lenses can cause double vision)
- cosmetic surgery (only reason for treatment)
how do you manage central suppression
- microtropia
- usually no treatment needed except for amblyopia
- beware as BSV slightly inferior to normal
what does a px with ARC see with the worth’s lights 4 dot test
exactly the same as a person with normal BSV despite the fact they have a manifest deviation
how do you manage ARC
- do not treat
- be aware that BSV slightly inferior therefore monitor
explain striated lens partial dissociation/bagolini lenses
- striations form a partial dissociation (control)
- spot light seen by both eyes
- striations are orientated in different directions for each eye
- the streak of light is seen separately by either eye
with bagolini lenses, which orientation does the patient report to see the streak of light in comparison to the striations on the lens seen by the optometrist
perpendicular
e.g. if px sees light at 45 degrees, optometrist sees striations at 135 degrees
describe the bagolini glasses test
- fixate a spot light (near or distance fixation and easiest with a bright pen torch)
- striations before the R eye placed perpendicular to striations before the L eye (normally 135 and 45 degrees)
- ask patient to report on how many lights they see
- ask them to draw the pattern they see
- are there any gaps in the centre near light
what happens in the bagolini test with right eye esotropia
- image hits nasal retina which projects temporarily
- px will see two lights
- one to the right which is seen by right eye
- uncrossed diplopia
what happens in the bagolini test with right eye exotropia
- image hits temporal retina which projects nasally
- px will see two lights
- light at right eye will be moved to the left
- crossed diplopia
what happens in the bagolini test with right eye suppression
will see light on the left only
what happens in the bagolini test with central/foveal suppression of right eye
streaks will be superimposed, but right streak will have a gap in the middle from suppression
what happens in the bagolini test with ARC
px will see exactly the same as a person with normal BSV despite the fact they have a manifest deviation
in the worth’s lights test, if a patient has suppression of their left eye, how many and which lights will they see
two red lights, vertical (the green horizontal lights will be missing as cannot see out of that eye)
in the worth’s light test, if a patient has suppression of their right eye, how many and which lights will they see
two green lights. horizontal (the red vertical lights will be missing as cannot see out of that eye)
