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Strabismus 106 > Suppression > Flashcards

Suppression Flashcards

1
Q

What is suppression?

A

A sensory adaptation that’s common in manifest strabismus. It’s a cortical inhabitation occurring in the visual cortex

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2
Q

What’s the suppressed area on the retina called?

A

A scotoma

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3
Q

What is physiological suppression?

A

To eliminate physiological diplopia or when using monocular instrument or used to suppress the peripheral visual field during intense concentration

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4
Q

When do people pathologically suppress?

A

In manifest strabismus, confusion or incompatible images. Can sometimes occur in latent strabismus or in anisometropic amblyopia.

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5
Q

What’s an elliptical scotoma?

A

In Esotropia the foveal suppression and the peripheral scotoma join

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6
Q

What’s a hemiretinal scotoma?

A

Suppression that is of half the retina to the temporal side . Common to have suppression on the temporal side up to the vertical midline.

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7
Q

What age is suppression unlikely to occur age?

A

10 years old

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8
Q

If a child had diplopia and a manifest strabismus, when would you assume this started?

A

Recently otherwise they’ve have suppression

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9
Q

When can you lose the ability to suppress?

A

E.g. after head injury

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10
Q

What is happening when elderly patients appear to have suppression (that isn’t residual from childhood)?

A

Ignoring - likely more psychological

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11
Q

How do we investigate suppression?

A
  • 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
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12
Q

What are the two ways of measuring suppression?

A

Loose Prisms or Synoptophore

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13
Q

How do you use loose prisms for measuring suppression?

A
  • 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
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14
Q

How do you use the synoptophore to measure suppression?

A
  • Same principle of prisms
  • Move tube
  • Record suppression scotoma in degrees
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15
Q

What is the post-operative diplopia test (PODT)?

A

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)

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16
Q

How do we use Prisms in Free Space as a post-operative diplopia test?

A
  • 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
17
Q

How do we use Botulinum Toxin as a post-operative diplopia test?

A
  • 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
18
Q

What did Khan et al (2008)’s study find about PODT?

A

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

19
Q

How does the Sbisa Bar or Bagolini Filter Bar work?

A

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

20
Q

How does the synoptophore work for measuring density of suppression?

A

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.

21
Q

What are the options for suppression treatment?

A

1) No treatment
2) Eliminate Suppression
3) Encourage Suppression
4) Restore Suppression

22
Q

Why would you not do any treatment for suppression?

A

In small angle strabismus, stable or asymptomatic patients

23
Q

What is ‘eliminating suppression’?

A

Promoting diplopia to then provide a stimulus for BSV, have to know they’ll achieve BSV

24
Q

When would you use ‘eliminating suppression’?

A

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.

25
Q

Why would you not eliminate suppression?

A

When there’s no binocular potential or in the presence of abnormal BSV

26
Q

What options are there for eliminating suppression?

A
  • Septum
  • Coloured Filters
  • Prisms
  • Red Filter Drawing
  • Synoptophore
  • Occlusion of Fixing Eye/ ALternating Occlusion
  • New Technology like Dichoptic Viewing
27
Q

What is a Septum for?

A

Eliminating suppression. Used in weak suppression/light. It is held between the eyes to aid awareness of the 2 eyes and so promotes diplopia

28
Q

What are coloured filters for?

A

For eliminating suppression .
Using either red-green goggles, sbisa or bagolini. The colours are used to show them something that they can only see with the suppressed eye. Use light to show this and cover test to demonstrate.
Red/Green = aim to remove one filter and retain diplopia
Sbsia = over the fixing eye with the aim to reduce filter and maintain diplopia

29
Q

How are prisms used in eliminating suppression?

A

Aim to move image out of the suppression scotoma. Use a small vertical prism of 10PD in front of the fixing eye with an aim to reduce the prism but have diplopia retained.

30
Q

How are red filter drawings used in suppression?

A

For eliminating suppression. A red filter is over the fixing eye and the patient is asked to draw with a red pen that’s complementary to the filter and thus cannot be seen by the fixing eye.

31
Q

How is a synoptophore used for eliminating suppression?

A

Use of the rheostat to dim the image in front of the fixing eye

32
Q

How is occlusion of fixing eye/alternating occlusion used in suppression?

A

Anti-suppression, for intermittent exotropia and isn’t the same as patching for amblyopia

33
Q

What is Dichoptic viewing?

A

New technology used for eliminating suppression. Computer and shutter glasses aiming to equalise the image seen by each eye by varying the contrast.

34
Q

How do we encourage suppression?

A

Occlude suppressing chosen eye using Blenderm tape or Bangerter foils, graded in density and the aim to encourage suppression but to gradually reduce foil density but maintain suppression.

35
Q

How do we move a diplopic image into the suppression area and what’s it for?

A

For treating suppression. Use of Fresnel Prisms to put the diplopic image back into the suppression area. Once stable we can incorporate into glasses. The aim is to reduce and eventually eliminate prisms whilst able to maintain suppression.

OR

Use Botulinum Toxin (BT/Botox) which is used to change eye alignment temporarily but with the how that suppression continues after it wears off

Strabismus 106 (35 decks)

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