Lecture 5

Question 1

What’s the significance of normal sensory fusion system and ocular alignment?

Answer 1

Ocular alignment of the eyes depends on a normally functioning sesnory fusion system.

Sensory fusion is the ability of the eyes to perceive the information from both eyes as a single image.

Question 2

What significance does motor fusion play in ocular alignment?

Answer 2

Ocular alignment of the eyes depends on a normally functioning motor fusion system.

Motor fusion is the ability to sustain that single image through a range of eye movements.

Question 3

How does pathological diplopia occur?

Answer 3

When the eyes are not aligned (a manifest strabismus is present) pathological diplopia will occur. This is because non-corresponding retinal points are being stimulated.

In the case of a constant or intermittent strabismus, diplopia will occur and will either be:

• consciously appreciated by the patient (when there is normal BV) or,
• not appreciated

Question 4

Can pathological diplopia occur in people with normal BV?

Answer 4

In those with normal BV and normally straight eyes:

• Pathological diplopia may occur if the eyes become misaligned (e.g. when fusion is not possible) - vergence failure

Question 5

What is contralateral image point (CIP)?

Answer 5

The location of the diplopic image will depend on the area of the retina stimulated.

The non-corresponding retinal points stimulated in the deviating eye is called the contralateral image point (CIP).

Question 6

Pathological diplopia is esotropia and exotropia?

Answer 6

Esotropia would result in uncrossed diplopia as the image falling on the temporal retina gets projected nasally.

Exotropia would result in crossed diplopia as the image falling on the nasal retina gets projected temporally.

Question 7

Answer 7

The star would fall on top of the heart

Question 8

What happens when different images are presented to each fovea?

Answer 8

When different images are presented to each fovea, they are superimposed. This is because both fovea have principle visual direction and are projected straight forward ahead (cylopean eye).

When this occurs it is called confusion.

This only occurs when there is NRc e.g. both foveas are cortically linked as corresponding retinal points.

Question 9

Why would you not have diplopia?

Answer 9

Having diplopia and or confusion can be very uncomfortable. The cortical response to diplopia that cannot be fused is to inhibit or suppress the diplopic image.

In the circumstance where there is a misalignment of the eyes present and the patient does not appreciate diplopia, suppression is occurring.

Question 10

Define suppression

Answer 10

Suppression is defined as:

The subconscious cognitive inhibition of visual stimuli, either partially or totally, in a binocular situation (e.g. both eyes must be open and seeing).

Suppression can be:

Physiological, pathological

Constant or intermittent

Unilateral or Bilateral or alternating

Question 11

Physiological suppression occurs in response to?

Answer 11

Physiological suppression occurs in response to:

Physiological diplopia:

You aren’t aware of the diplopia images in front of and behind fixation.

Retinal rivalry:

When dissimilar images are presented to both fovea (corresponding retinal points) images are superimposed but not fused. The individual will see both images, but will alternate between them (alternating the other image)

Question 12

Pathological suppression occurs in response to?

Answer 12

Pathological suppression occurs in response to:

Diplopia: images stimulating non-corresponding retinal points

Confusion: different images falling on each fovea

Incompatible images: as in anisometropia where the images may be different in size, shape and clarity preventing central fusion (peripheral fusion still occurs)

Question 13

Pathological suppression in manifest strabismus

Answer 13

In the case of a manifest strabismus that is present from childhood, the brain chooses to ignore one image (suppress) when the patient is viewing with both eyes open.

Suppresion is a BINOCULAR ANOMALY, i.e. you need to have both eyes open for it to occur. It is not a blind eye.

When you cover the non-suppressing eye (the fixing eye) the suppressing eye will see the fixation target.

Question 14

Pathological suppression in adults and children

Answer 14

Pathological suppression develops very rapidly in response to diplopia in young children. This corresponds to the period of neural plasticity. Slower suppression development occurs in older children.

Adults may however learn to ignore one image over time. Once suppression develops in childhood it will remain throughout life (unless treated)

Question 15

What is suppression scotoma?

Answer 15

The area and density of the suppression varies depending on the binocular condition. Generally, only part of the retina in the deviating eye is suppressed.

The retinal area which is suppressed is called a ‘suppression scotoma’.

In manifest strabismus, suppression generally includes the fovea and CIP.

Question 16

Pathological suppression in Esotropia

Answer 16

In ET the suppression tends to be elliptical in shape incorporating the fovea and CIP with the size depending on the size of the deviation.

Suppression at the fovea is very dense, with the density decreasing into the peiphery.

Question 17

Pathological suppression in exotropia

Answer 17

In XT, the suppression scotoma may be elliptical or incorporate the whole temporal retina.

Question 18

Intermittent, alternating pathological suppression

Answer 18

The suppression scotoma may be present intermittently, only when required, e.g. intermittent strabismus.

It can also alternate between eyes, depedning on which eye is deviating and which is th efixing eye.

Alternating suppression is especially common in children with large infantile strabismus and cross-fixation behaviour.

Question 19

Investigation of suppression

Answer 19

Cover test:

Manifest deviations - appreciation of diplopia

Intermittent and decompensating latent deviations: recovery of BSV on CT-slow or sluggish recovery can indicate suppression is impacting the strength of BSV

Worths lights: absence of one set of lights

Bagoline glasses: part or all of the image to one eye is missing

Synoptophore: missing images, parts of images or controls

Appreciation of diplopia when beyond the range of motor fusion

Question 20

Sbisa Bar

Answer 20

To measure both the density of the suppression and the size of the suppression scotoma, a sbisa bar can be used.

The patient fixates on a torch and the intensity of filter over the fixating eye is gradually increased until the deviating eye moves to take up fixation.

Question 21

Use of synoptophore in suppression

Answer 21

Synoptophore: Adjusting the rheostat in front of the suppressing eye to increase the brightness of the image and decreasing the brightness to the contralateral eye.

Continue until both images are seen.

Measuring the depth of suppression is only relevant when assessing the progress of treatment

Question 23

Qualitative and quantitative measurement of suppression

Answer 23

Measurement of the area of suppression is performed either qualitatively or quantitatively

Qualitatively: on the synoptophore, the slide size (using fusion slides) is increased until both of the image controls are visible outside the scotoma.

Quantitatively: by mapping the boundaries of the scotoma by moving the image until it is seen (with prisms or the synoptophore)

Question 24

Treatment of suppression

Answer 24

Remember that the presence of suppression is usually a good thing. There are treatments that can be conducted at home and in clinic to eliminate supression to improve binocular functionality and control of a deviation. BUT, these should be performed at patients with:

• Latent or intermittent deviations or
• Before surgery for those with the potential for BSV, e.g. late onset constant strabismus

The aim of treatment is to allow for appreciation of diplopia/ teaching the patient to recognise the second image. This is often used as a starting point for treatment. The elimination of suppressio itself can help improve BSV (the presence of suppression can be a barrier to BSV)

Question 25

Red filter and light

Treatment of suppression

Answer 25

• Can be performed at home or clinic
• At a point where diplopia should be appreciated, near or distance, a light is used for the patient to fixate on
• A red filter or sbisa bar (ref-green glasses can also be used) is placed over the deviating eye to increase the awareness of the image
• Filters are increased until both images are seen and gradually decreased until diplopia can be appreciated without filter

Question 26

Red work/ Red filter drawing

Answer 26

• A red filter is placed over the non-suppressing eye and the child draws or performs a written task with a red pen
• Both eyes are able to see the paper, while only the suppressing eye is able to see the drawing.
• This forces the suppresing eye to work
• Could be performed for up to 30 minutes per day until suppression improves

Question 27

Septum and Prsims in treatment of suppression

Answer 27

Septum:

A piece of card is placed vertically along the nose and between the eyes to separate the images and prevent fusion. The septum can be made smaller and or transparent until the diplopia can be appreciated without it

Prisms:

Vertical prisms can be used to move an image outside the suppression scotoma. Gradually the prisms strength is reduced while the patient tries to maintain the two images

Question 28

Synoptophore in treating suppression

Answer 28

A number of methods on the synoptophore can be used to increase awareness of the suppressed image.

• Increasing the brightness of the image to the suppressed eye
• Flashing the image on and off
• Moving the image

Question 29

When is treatment of suppression necessary?

Answer 29

Treatment of suppression is necessary when:

• The suppression precludes you performing other orthoptic treatment
• Convergence excercises
• Treatment of intermittent deviations

When the suppression is a barrier to BSV in someone with a latent or intermittent deviation

Question 30

When shouldn’t we treat suppression

Answer 30

To treat suppression, you must first teach the patient to appreciate diplopia. This can be dangerous as it can lead to intractable diplopia i.e. diplopia that can no logner be ignored

You can avoid this by choosing the patient carefully:

• Treating suppression in the presence of a constant deviation (that has never bee latent or intermittent) is a bad idea
• IF no binocular vision, do not treat
• After the age of plasticity, avoid treating

Question 31

The dangers of not investigating

Answer 31

In the case of strabismus surgery after the age of plasticity, the presence of suppression can be a really good thing!

It helps avoid post-op diplopia.

BUT, it is important to make sure that the surgery the point of fixation remains insdie the suppression scotoma to prevent intractable diplopia. So, the area of suppression scotoma needs to be investigated with a post-operative diplopia assessment.