suppression Flashcards
what is suppression
a sensory adaptation to (likely manifest) strabismus
sensory adaptations - are the brains ways of dealing with the manifest strabismus in the eyes and you dont want to be left with diplopia - their are ways of dealing with that e..g shutting off the signals from the confusing area - that would give you double vision
- rarely ignores the entire retina of one eye - but usually ignores an area of the retina of one eye
define suppression
- the mental inhibition of visual sensation in one eye in favour of the other when both eyes are open - if you have a deviating eye and you occlude the other eye then you actually find that their isnt that area of suppression- when the strabismic eye is left on its own
when one eye is strabismic - i.e. not pointing in the right direction - their is suppression of that area that confuses the signals and the imaging of what we are trying to look at - however if you close the favoured eye by suppression and leave just the strabismic eye then you dont have suppression anymore
this may occur in bincoular single vision where a small area of the fovea may be suppressed - which is called central suppression - and it still leaves peripheral fusion of the two eyes
and in manifest strabismus
it may vary in area and density - i.e. you could suppress either all of your temporal retina or all of your nasal retina- very rare that the entire retina is suppressed
a defined area is known as a scotoma
rarely if ever an entire eye is totally suppressed
what does density of suppression refer to
- how well established the suppression is
i. e. if you try to make it hard for the fixing eye to see - what happens then? - do they continue to suppress - or do they switch and use their suppressing eye
what is the area that is suppressed on the retina called
the area on the retina that is suppressed is known as a scotoma - when both eyes are open
it is rare if ever that a entire eye is suppressed - usually you have a region of suppression which can vary in size, width and how deep it is + how dense it is
what are reasons for suppression
to eliminate diplopia and confusion
physiological - to eliminate physilogical diplopia( this is normal) - this is something you have when you have normal bsv - when your looking at something near the things in the far distance double - when your looking in the distance and you introduce something near - your finger appears double
when using a monocular instrument - microscope to suppress the peirpheral field during intense concentration
pathological - to eliminate symptons when fusion cannot be achieved - fusion cannot be achieved in the presence of a large manifest strabismus
without a sensory adaptation their would be diplopia - where you see two of the image or confusion where you see two seperate images in the same visual space overlapping each other
what are characteristics of suppression
- the retina does not switch itself off - it dosnt not send signals - suppression is a cortical function - the mental inhibition - the brain is ignoring the signals from that area of the retina
although a cortical function (it is being conducted by the visual cortex) it is a area of the retina that is being suppressed
suppression of the fovea to eliminate confusion is usually the first occur
an area around the point of diplopia- wherever the diplopic image is being recieved occurs next
when you have a esotropia - the point recieving the diplopic image and the fovea join up this usually produces a elipitical scotoma - which is between the area of the retina being stimulated by the diplopic image and the fovea
describe projection in esotropia
in the esotropic eye the fovea will be outwardly displaced meaning the eye is turning inwards
the nasal retina is being stimulated - the nasal retina projects temporaly
their is another image that falls on the fovea of the esotropic eye so that image will project as if it straight ahead - so you have confusion - two images being projected to the same area visual space
what is confusion
two images being projected to the same area of visual space
describe the area of suppression in esotropias
their is a eplicitcal suppression area that forms - starts at the fovea and then goes on to develop around the point that is receiving the diplopic image and then the areas join up - the point between the fovea and the point recieving the diplopic image which is a approxiamtley the angle of deviaiton forms the elipitical scotoma this area becomes suppressed
how does suppression in exotropia differ
in exotropia supression is more widespread and may be hemiretinal (half of the retina ) to the temporal side
suppression is dependent on the type of deviaiton is present
in intermittent strabismus pathological supression may occur when the manifest deviation is present - most commonly seen in a intermittent distance exotropia - where your looking at something near and you have bsv - you look at something in the distance and one eye deviates and the other eye deviates - and suppression occurs in the childhood onset of strabismus when either eye is deviaiting
in alternating deviaitons the suppression alternates with alternating fixation
in alternating deviaitons the suppression alternates with alternating fixation
when does suppression develop
suppression develops rapidly in infancy
suppression develops less rapidly as the child gets older and is unlikely to occur after the age of 10 years
elderly patients suffer with acquired strabismus with diplopia and confusion because the suppression is unable to develop
elderly patients can often ignore diplopia more readily than younger adults but is probably not true suppression
what tests can you conduct to investigate the presence of suppression
worth lights
bagolini glasses
suppression plates on stereotests
polaroid 4 dot test
4 prism test
if somebody had left suppression what would they see on the worth lights
two red lights
if someone had right suppression what would they see in worth lights
3 green lights
what would somone with alternate suppression see on worth lights
2 red and then 3 green and then keep on alternating
if someone has diplopia what would they see on worth lights
5 lights
what would you see if you had a incomplete line through the cross on bagolini glasses
central suppression
what is the 4 diopter prism test
you put a 4 diopter prism up over the eye and see if their is a movement of the eye behind the prism which will tell you weather central suppression is their or not
how do you investigate the area of suppression
prisms
synoptophore
central suppression- 4 diopter, base in and base out
polaroid 4 dot
macular worth lights
what is the post - op diplopia test
if someone has a area of suppression and they are going to have surgery
e.g.. if someone has a esotropia and they have a elipitical area of suppression and you do surgery to correct them the danger of that is you could give them diplopia after the surgery as you might put them outside of their suppression zone - e.g. if the suppression zone goes just up to the fovea if you put them on the fovea they may suffer from diplopia afterwards because you have stopped the image from landing in the suppressed region and they are beyond the age where suppression could redevelop
so sometimes you would undercorrect the deviaiton because you dont want to leave them with diplopia - having taking them out of their suppression zone
how would the post diplopia test be used to check an area of suppression
- move image across the retina using prisms and asking them if they see one or two images - where they begin to see two images we know that they are outside of their suppression zone
you place the prism in the direction of the deviaiton and you overcorrect to determine the range
e.g.. it someone has a 20d esotropia you would put up base out prisms in front of the esotropic eye and you would increase the prisms asking the patient if they could see one image or two
if they had diplopia from a 18 diopter prism and you went up to 45 diopters and they remained diplopic you would know that their suppression zone was from 0- 18 diopters and they would be diplopic beyond that so you would undercorrect that patient for surgery
how would you use botulitim toxin to test for suppression area
inject muscle to paralyse and change deviation and asess diplopia in free space
e.g. if they had a esotropia you would inject the botox into the medial rectus and that would induce a paralysis into the medial rectus and would work so that the lateral rectus was working unopposed and was in a straighter direction
how would you test for the area of suppression in a esotropia
when you put up a prism in front of the eye and the light is falling on the fovea - you will see no movement
this is why you would see no movement on the 4 diopter because it is falling within the suppressed region and they eye is not responding behind the prism - when you get beyond that area you begin to get double
by increasing the prism you can see how large the area of suppression is and that can help them plan for surgery
how would you conduct the post op diplopia test using prisms
test for risk of diplopia following surgery
base out for esotropia
base in for exotropia
increase strength until diplopia is noted- because beyond that you are beyond the suppression scotoma and you would record that as the strength of prism which elicts diplopia
record strength of prism which elicits diplopia
can record graphically
how would you conducts a post op diplopia test using botulitium toxin
- if high risk of diplopia found with prisms bt is injected onto appropriate muscle
medial rectus esotropia
lateral rectus exotropia
bt takes 4 months to wear off
more realistic and longer to adpat to a new angle
how would you investigate the density of suppression
once you have investigated the area of suppression you would investigate the intensity of the suppression
sbisa bar/bagolini filter bar
16/17 filters
introduce the lowest filter in front of the fixing eye (straight eye) not the strabismic eye e.g. if they have a right esotropia you put it in front of the left eye
- you ask them to see the eye and if it is white or pink ask them if they can see the light and what colour it is if they start to develop diplopia and you get beyond their area of suppression they may start to see diplopia - so you would write - patient saw diplopia at filter 16 - that would be very established diplopia
if they saw diplopia at filter 2 or 3 that would be very low density of suppression and that would mean you wouldnt want to patch them because you may dirsrupt the suppression
as you go through the filters it gets harder for the patient to look through them
if a patient has light suppression they will switch and they will start to look with the other eye
if they have very dense suppression they wont switch and they will continue to look even when it is a very dark filter
you show the patient your pen torch
increase filter until diplopia occurs
occasionally red light becomes white as swap fixation
how do you measure the density of suppression on the synoptophore
turn down rheostat in front of the fixing eye until both pictures can be seen- only suitable for light suppression
change where the image lands on the retina - you can find out when they see the two images or when they switch the images off
what are some of the indications to eliminating suppression
suppression stops you seeing two images in the same point of space - it stops you seeing diplopic images - but their may be reasons why you would want to stop suppression
if you have a intermittent deviaiton that needs treatment - a patient will have to know that they have diplopia in order to overcome it and fuse it - so it may be helpful to help the patient
e.g. decompensating heterophporia (possibly convergence insufficency) e.g. they have a esophoria and it is becoming manifest you want them to continue with bsv so if you help them become aware when its mainfest then they can respond to that by fusing
patient is unable to fuse their eyes well and they suppress one eye and the eye drifts off if you can help them become aware of when their eyes are not straight and they are not symmetrically together to the near object - you can help them to become aware of the diplopia and fuse
late onset esotropia with a known history of bsv - they should be able to fuse if they have a history of bsv
if child is young enough to re- supress if fusion is not achieved - this is least common
what is intractable diplopia
diplopia that you cant cure i.e. they have diplopia and their is nothing that they can do to fuse
if you are going to eliminate suppression what must you be sure of
that they are able to fuse diplopia so taht you dont give them intractable diplopia
what are contra indications to eliminate suppression
no binocular potential- no possibility of fusing therefore you dont want to give them intractable diplopia
older patient with dubious bincoular potential
if you are going to interfere with suppression ensure that the patient is able to fuse
in the presence of abnormal bincoular single vision (abnormal correspondence) - where you have a eye that deviates i.e. a right esotropia you have a elipitical area of suppression i.e. foveal scotoma where they are suppressing that area of the retina - but another option for the patient would be that the area of the retina that is recieving the image becomes adopted by the brain like a pseudo fovea
what is abnormal correspondence
where the fovea of one eye does not correspond to the fovea of another eye - it corresponds to a psuedo fovea - i.e. a point on the retina that is recieving the image
if someone has abnormal correspondece you dont want to give them anti- suppression therapy
what are the two different sensory adaptations to deviaitons
- 2 different sensory adaptations to a manfiest strabismus= suppression and abnormal correspondence
- where you have a eye that points in a different direction either the cortex might inhibit the reception of that area of visual signalling from the retina or it may adapt to it and use it as if it was a fovea
how do you use a septum to treat suppression
- it spilts the patients visual field and aids the patients awareness of 2 different images from 2 different eyes and therefore aids the promotion of diplopia
suitable for light density of suppression
splits the visual fields
aids awareness of two eyes and therefore the promotion of diplopia
how would you treat suppression using red and green googgles and a light
this is a more dissociating test
will appreciate one light either a red or green
use cover test to demonstrate two images
remove the filter in front of the suppressing eye
remove filter in front of the non- fixing eye
you are showing them that they have 2 different images and you are increasing their awareness of their eyes recieving different images - your increasing their awareness of the suppressing eyes image
how would you treat suppression using a sbisa bar/ bagolini filter bar
to use it to measure the density of suppression you put it in front of the fixing eye and you see when they swap to the suppressing eye to see when they become aware of two
to use it to treat suppression - you make the stimulus’s’ in front of the eye very different first and then you decrease the difference and enourage them to still be aware that they have two images their
- you would use a strong filter first - the darker filter first - this would make them aware of two different images - they would see a white light with no filter and then a strong red filter with the other eye - and then you gradually reduce the filter down asking them if they can still see two images - so that when you remove the filter they still have two images because they have got the manifest strabismus and they have two images of the light - you are encouraging them to maintin diplopia as the stimulus gets less dissociative
- you start with a dissociative stimulus and you dissociate it less as you go along making them more aware of the other image
place filter which promotes diplopia in front of the fixing eye
reduce filter encouraging patient to maintain diplopia
continue until diplopia is appreciated in free space
how would you treat suppression with prisms
you would use prisms to make the patient aware of the diplopia
normal vertical prism fusion range = 3 diopters base up - 3 diopters base down - in conditons such as thyroid eye disease it may increase
normal ranges for prism fusion range
near 15 base in
35-40 base out
distance 5-7 base in and 15 base out
- use small vertical prism in front of the fixing eye to promote diplopia - people cant fuse a vertically dissociated image so you can use vertical prisms to make them aware of diplopia use a small diopter prism e.g. 5-6 diopter prism pr 10 diopter prism in front of the fixing eye and that promotes diplopia - because of the nature of the suppression zone being eplitical - it takes you beyond the suppression zone - as you are decreasing the prisms you are going to the boudaries of the suppression area and you are trying to get that suppression area to shrink
- you start with diplopia and then gradually reduce the strength of the prism and encourage the patient to maintain diplopia
reduce prism encouraging diplopia to be maintained
can use horizontal prisms but it is a lenghtier process
how would you use a red filter drawing to treat suppression
you would put the red filter over the fixing eye and you would get the patient to draw with the complementry (identically coloured) red pen
the patient will see the page with both eye but the drawing will only be seen by the suppressing eye (eye without the filter)
red is chosen as it is thought to stimulate the fovea
often aids control rather than promoting diplopia
often used in accomodative esotropia
how would you use the synoptophore to treat suppression
compress the suppression scotoma
encourage superimposition by moving the fixing picture and the patient subjectivley moves the other to it - you would use the lion and the cage - they are looking at the lion and the cage and they are supressing the cage - as you move the bar backwards and forwards you are moving the image
when they are supressing they dont see the image - but you take them beyond their suppression scotoma so that they are aware of the two images - and then you gradually move the images towards each other and ask the patient if they can still see the lion and the cage - so you can try and shrink the suppression zone by pushing the images together - increasing their awareness of the suppression scotoma boundaries
how would you use occlusion to treat suppression
you cover the good eye
- promotes awareness of suppressing eye
often used as a continuation of amblyopia therapy - it treats amblyopia and makes them more aware of that eye
check the sbisa bar- because if they have low density of suppression - e..g.g. it is not very well established and they have no potential for fusion then you dont want to decrease their suppression -
if you had a patient who had awareness of diplopia at filter 2 on the sbisa bar then you wouldnt patch them because you wouldnt want them to anti- suppress
if you are tyring to get a patient to suppress because you know that they have fusion that would be light density of suppression
what is new treatment of suppression
uses computer technology and shutter glasses ]
aims to equalise image seen by each eye by varying the contrast
what are bangereter foils
paritally occlusive filters
the most dense allows perception of light only
the least dense may allow 6/6 vision
their is a diagnostic bar
place the bar over the non fixing eye and increase the foils until single vision is achieved - you are using the light filter and you are placing it over the non fixing eye so the suppressing eye and you are increasing the foil until they become unaware of the diplopia
the filter is applied to glasses- the aim is to reduce and then discard the foil
