Sensory Fusion Flashcards
What is Worth’s 3 grades of BV?
Simultaneous Perception
- ability to use both eyes at the same time
Fusion
- sensory fusion
- motor fusion
Stereopsis
- use of BV to see in 3D
What is sensory fusion?
What is needed to fuse images?
‘Integration of 2 similar images, one formed on each retina into one image within the brain’
Images must be:
- Similar in brightness
- Similar in size
- Similar in form
When do you assess sensory fusion? What type of patients?
In patients with strabismus (some sort of tropia)
In patients with strabismus - what needs to be worked out in order to give treatment? Why?
Whether they have: 1 - Confusion 2 - Pathological Diplopia 3 - Suppression 4 - Abnormal Retinal Correspondence
Due to the management for each of these being different.
Can also carry out test on those with heterophoria to confirm they have normal BSV.
In confusion… what does the cyclopean eye see in:
- Esotropia
- Exotropia
The brain sees the superimposed images therefore confusion.
ESOT - superimposed images - uncommon
EXOT - superimposed images - uncommon
When does confusion and diplopia occur?
Confusion and Diplopia usually occur after the age of 8 years old.
In pathological diplopia… what happens when its:
- Esotropia
- Exotropia
The points are not corresponding and therefore seeing double.
ESOT:
- Strabismic eye –> The fixation object is imaged on the nasal retina and therefore projected temporally
- Uncrossed diplopia: RE sees to the RHS
EXOT:
- Strabismic eye –> The fixation object is images on the temporal retina and therefore projected nasally
- Crossed diplopia: RE sees to the LHS
When does suppression begin?
- Begins in children under 8 years old
What is constant suppression?
- One blind eye
- Constant manifest strabismus suppression of the non-dominant eye/non-fixating eye
- Can be RE/LE or alternating suppression
Child suppresses and switches off the 2nd image to see singly.
What is partial suppression?
When only part of the image in one eye is suppressed.
e.g. macula/foveal suppression with peripheral BSV
only part of the image is suppressed
What is intermittent suppression?
When suppression happens in some circumstances only
Otherwise Diplopia or BSV.
e. g. in the distance
- Px has normal BSV at near and has sensory and motor fusion and stereopsis but not normal BSV at distance.
How do you investigate suppression?
Diagnose the presence of suppression
e.g. show them a lion and a cage and ask what they see
The size and position of the scotoma:
- Can be central suppression with peripheral fusion.
- Can measure size of scotoma with prisms
(imp. if you are moving eye and do surgery so you dont leave them with dipl. )
Density of suppression may vary:
- Measured with sbisa bar
- Measured with NDF bar
How do you measure area suppression (suppression scotoma)?
- Measure with prisms
- Prism placed in front of deviated eye
- Prism increased until Px notes diplopia
- Recorded for base out, base in, base up and base down
e.g. L EXOT - therefore put prism in front of left eye and show Px a light. If they have suppression, they will see one light as they’re suppressing.
Increase the prism until the Px has double vision or sees the two lights.
How do you measure the density of suppression?
- Graded bar of varying density of red filters placed in front of the fixing eye.
- Px requested to view light and asked what colour
Filters are slowly increased in strength:
- Px informs when the light changes from red to white (increasing the density of the filter and so becomes darked and darker and makes it difficult for the eye to see with. The point where that eye becomes impaired, the Px now fixates with the other eye to compensate and will see a white light - record the density of the filter or one just before)
- Or if examiner has seen fixation swap
- Or Px reports diplopia (seeing two lights as no longer suppressing)
