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 (Binocular Sensory vision)to see in 3D
Which worth’s 3 grades is needed to achieve the best BV/binocular function
- simultaneous perception
- Fusion (sensory and 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 does a sensory fusion test help you identify?
Which of the following conditions a patient with strabismus has:
- confusion
- pathological diplopia
- suppression
- abnormal retinal correspondence
Occasionally you use it to confirm that a patient has normal BSV.
Why must we know which condition a patient has?
Because management for each condition is different.
In which type of strabismus may you experience confusion?
- eSotropia (SOT) - one eye is turned in whilst for the other eye, the picture lies on the fovea. Thus the cyclopean eye sees superimposed e.g. tree and house
- eXotropia (XOT) -one eye is turned outwards whilst for the other eye, the image lies on the fovea. cyclopean eye sees superimposed tree and house
After what age does pathological diplopia occur in a strabismus patient?
8 years old
How does pathological diplopia occur?
- eSotropia (SOT) In the strabismic eye - fixation of the object is imaged on nasal retina (rather than the fovea) thus it is projected temporally. From the diagram you can see what the cyclopean eye would see. This is uncrossed diplopia.
- exotropia (XOT) In the strabismic eye fixation of the object is imaged on the temporal retina which is projected nasally. Following the diagram to see what the cyclopean eye would see.
[The way to tell whether diplopia is crossed or uncrossed is to see where the ‘fake’ image is produced - if it is on the side of the strabismic eye then its uncrossed diplopia, if its on the other side then it is crossed diplopia]
At what age does pathological suppression begin?
Begins at under eight years old.
What is constant suppression?
When both eyes are open, ‘false’ image from the strabismic eye is ignored thus the patient experiences no diplopia nor confusion.
Occurs in constant manifest strabismus where we have complete suppression of the non dominant/non fixating eye.
This can exist in the right eye or left eye or be an 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 occur at intermediate distances
How do you investigate suppression?
- Diagnose the presence of suppression
- measure the size and position of the scotoma (important for surgery) -it can be central suppression with peripheral fusion - can measure size of scooter with prisms
- measure the density of suppression -This can be measured using a sbisa Bar or a Nuetral Density Filter (NDF) bar
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 (neutral density filter) bar
What is area suppression also termed as?
suppression scotoma
How do you use prisms to measure suppression scotoma?
The prism is placed before the deviated eye And a light torch is flashed infront of their eye. The prism increased until patient notes diplopia (which is out of the area of suppression) The amount of prism needed is recorded for base out, base in, base up and base down.
How do you measure the density of suppression with a sbisa bar?
- The sbisa bar is a graded bar of varying density of red filters so its light red to dark red at the bottom, eventually the colour gets so dark it oculdes the eye.
- It is placed infront of the fixating eye (the non strabismic eye) - px is requested to view light (in front of fixating eye) and asked what colour the light is which will be red as it will be viewed by fixing eye at first.
- filters slowly increased in strength/darkness until px cannot see through the filter
There are three outcomes that shall occur which indicate the density of supression:
- patient informs examiner when the light changes from red to white as they have to use their strabismic eye in order to see
- or examiner will see fixation swap between eyes (i.e. strabismic eye moves in to focus)
- or px reports diplopia In either of these cases you record the filter just before any of these three things happened.
A score of less than ten indicates their supression is weak.
If density falls below ten what are we in danger of?
We are in danger of removing their supression area and leaving them with intractable diplopia when we do surgery.
What happens in abnormal retinal correspondence
Fovea of strabismic eye learns to correspond a non-foveal area as the fovea (pseudo fovea) and then all the retinal correspondence in the periphery also shifts so essentially they have satisfactory BSV (binocular single vision like me and you).
Only thing that might not be as great as a person with normal BSV is stereopsis.
What is total dissociation and how is it tested for sensory fusion?
DIFFERENT targets/images are seen by each eye (each eye has a different viewing tube).
What is partial dissociation and how is it tested for sensory fusion?
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 and vice versa. Then you would ask the patient what they saw and if they didn’t see a part of the image that would e.g. be seen by the right eye then you can conclude Px has right eye supression.
[e.g. the picture attached]
Describe the set up for worth’s lights 4 dot test and how it works:
- four lights, usually round but can be different shapes 2 green 1 red 1 white
- You view these through red and green goggles
Red filter before Right eye and Green filter before Left eye
How it works is:
Green is not transmitted through a red filter and Red is not transmitted through a green filter
White is transmitted equally through both filters - thus white light which shall appear red through the red filter and green through green filter.
The white dot acts as the control.
The px wears the goggles.
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?
[The picture refers to what eyes with good BSV would see]
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
Px 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’s a synoptophere?
The machine used to test total dissociation.
