Suppression Flashcards
What is suppression?
A sensory adaptation that’s common in manifest strabismus. It’s a cortical inhabitation occurring in the visual cortex
What’s the suppressed area on the retina called?
A scotoma
What is physiological suppression?
To eliminate physiological diplopia or when using monocular instrument or used to suppress the peripheral visual field during intense concentration
When do people pathologically suppress?
In manifest strabismus, confusion or incompatible images. Can sometimes occur in latent strabismus or in anisometropic amblyopia.
What’s an elliptical scotoma?
In Esotropia the foveal suppression and the peripheral scotoma join
What’s a hemiretinal scotoma?
Suppression that is of half the retina to the temporal side . Common to have suppression on the temporal side up to the vertical midline.
What age is suppression unlikely to occur age?
10 years old
If a child had diplopia and a manifest strabismus, when would you assume this started?
Recently otherwise they’ve have suppression
When can you lose the ability to suppress?
E.g. after head injury
What is happening when elderly patients appear to have suppression (that isn’t residual from childhood)?
Ignoring - likely more psychological
How do we investigate suppression?
- Worth Lights
- Bagolini
- Suppression plates on stereotests (TNO, Wirt & Randot)
- Polarised 4-dot test for suppression central at 6m
- Prism Reflex Test
- 4PD Reflex Test for suppression around fovea or macular worth lights at 1/3m for central suppression
What are the two ways of measuring suppression?
Loose Prisms or Synoptophore
How do you use loose prisms for measuring suppression?
- Prism in front of deviating eye
- Increase prism strength
- Until report diplopia and thus no longer suppressing
- Repeat with horizontal (BO & BI) & vertical (BU & BD)
- Record prism size and direction where last maintained suppression
- Measure in PD
How do you use the synoptophore to measure suppression?
- Same principle of prisms
- Move tube
- Record suppression scotoma in degrees
What is the post-operative diplopia test (PODT)?
Used pre-operatively to aid in strabismus management decisions. If they don’t have BSV they must investigate the scotoma and risk of diplopia if the deviation were to be corrected with surgery tested using either prisms in free space or with Botulinum Toxin (BT/Botox)
How do we use Prisms in Free Space as a post-operative diplopia test?
- Prisms in front of deviating eye
- Ask if experiencing diplopia
- Eso - BO to correct ET
Exo - BI to correct XT - Reduce the deviation by increasing prism strength
- Corrected - angle of strabismus neutralised
- Under or Over Corrected -> from 20PD
- Near & Distance
- Record when suppressing and getting diplopia
How do we use Botulinum Toxin as a post-operative diplopia test?
- Botox is inserted into an extraocular muscle
- Reduces the deviation and ask if diplopia
- Eso = BT into the MR
Exo = BT into the LR - Offered to patients that are ‘high risk’ predicted by the PODT with prisms in free space
What did Khan et al (2008)’s study find about PODT?
Of 195 high risk diplopia patients with prisms 14 (7%) developed diplopia, 9 (4.6%) found it troublesome and of the others 5 (.6%) elected to have surgery along with the 181 (93%) who didn’t experience diplopia
How does the Sbisa Bar or Bagolini Filter Bar work?
16/17 filters from faint to dense red. Want to increase until they see 2 lights and state colours that they’re seeing on both (they may alternate fixation which you can tell as they will report still just on light but will be white as no longer the red one under the sbisa bar)
You increase filter until:
1) Diplopia occurs = no longer suppressing
2) Swaps fixation but still suppressing and may maintain suppression
3) At the end of the bar = no diplopia and no fixation swap
Record what happened at each filter e.g. suppression to filter 4 and diplopia at filter 5
How does the synoptophore work for measuring density of suppression?
Similar principle to Sbisa Bar
Rheostat is the illumination dial. Turn down the rheostat in front of fixing eye until both pictures can be seen and record using a 0-10 scale. However, this is only suitable for light suppression.
What are the options for suppression treatment?
1) No treatment
2) Eliminate Suppression
3) Encourage Suppression
4) Restore Suppression
Why would you not do any treatment for suppression?
In small angle strabismus, stable or asymptomatic patients
What is ‘eliminating suppression’?
Promoting diplopia to then provide a stimulus for BSV, have to know they’ll achieve BSV
When would you use ‘eliminating suppression’?
Used for intermittent deviations or in decompensating heterophoria (where latent the majorly of the time) or when there’s a late-onset esotropia with previous history of BSV.
